3D and 2D metal halide perovskites (MHPs) and perovskite derivatives have provoked a substantial revolution in the field of photovoltaics and optoelectronics because of their superior optical characteristics, physical properties’ tunability, ease of fabrication, and low cost. In very recent times, MHPs have attracted a significant interest for their possible use in various photocatalytic applications. The suitability of MHPs in relevant solar-driven reactions comes essentially from their highly tunable and narrow band gap, long carrier lifetimes, and high mobilities, together with a good defect tolerance. In addition, their band alignment, relative to the potentials of common redox half-reactions, indicates the thermodynamic suitability of these materials to effectively run reduction reactions (H₂ generation, CO₂ reduction) and even oxidation reactions for MHPs with higher band gap values (e.g., chloride-based).¹ In this presentation, we will provide an overview of the research activity currently running in our research group aiming at exploiting the full potential of MHPs for solar fuel production. In particular, we will show how a rational materials chemistry engineering can be applied to modulate the photocatalytic properties for the intended solar-drive reaction. In addition, strategies to boost the activity through heterojunction design will be presented. Finally, through a combined experimental and computational modelling work details about the underlying mechanisms for hydrogen photogeneration and nitrogen fixation will be presented.^2–4

Mono- or di-ammonium cations are commonly used to enhance the performance and stability of perovskite solar cells (PSCs) via surface defect passivation.^1,2 However, their effectiveness is still limited by the little understanding of the structure-property-performance relationship of the capping layer/3D perovskite stack.³ This work explores how the molecular geometry of diamine spacers affects the structure, properties, and performances of low dimensional (LD) capping layers on top of 3D perovskites, and their impact in solar cell devices. Two diamine spacers with similar chemical composition but different molecular geometry are tested: 4,4′-Dithiodianiline (2S) and 4,4’-Ethylenedianiline (ET). In 2S, the two amine groups are spatially close owing to a torsion in the backbone of the molecule. Instead, in ET the amine groups are at the maximum distance. The torsion allows 2S to bind to neighboring vacancy sites at the surface of the perovskite lattice, enhancing its passivation capabilities with respect to ET. The 2S spacer forms a 2D metal halide phase at the perovskite surface, which offers better charge extraction properties than the 1D phase induced by ET spacer. In solar cells incorporating 2S, these properties result in a power conversion efficiency (PCE) of 20.72%, improved from the 18.36% PCE of the reference. The ET spacer lowers the PCE to 15.67% due to less effective interaction with defect sites and lower charge extraction efficacy. Our results suggest that the double amine binding by the 2S spacer stabilizes the performance of the solar cells, enabling almost no loss of efficiency after 1000 hours under constant illumination in inert atmosphere.

Lead halide perovskite nanocrystals (LHP NCs) exhibit instability due to the dynamic and labile nature of both their inorganic core and the organic-inorganic interface, adversely impacting their optical and electronic properties [1]. The quest for novel capping ligands has not stopped, rather contrary [2], given the ever-expanding expectations for LHP NCs' deployment as classical and quantum light sources [3, 4]. We hypothesized that the facile molecular engineering of sulfonium salts as X-type ligands could enable highly customized surface chemistries for LHP NCs. Molecular dynamics simulations indicated that sulfonium ligands with diverse tail and headgroup structures exhibit equal or greater affinity to CsPbBr3 surfaces compared to their broadly studied ammonium counterparts. CsPbBr3 NCs capped with sulfonium bromides exhibit photoluminescence quantum yields exceeding 90% in colloids and enhanced durability in the typical purification processes. The compactness of the headgroup and tail branching significantly govern the long-term colloidal stability and resilience towards dilution and concentration. Further molecular engineering of sulfonium ligands allowed venturing into more demanding MAPbBr3 and FAPbBr3 NCs (MA, methylammonium; FA, formamidinium).

Metal halide perovskite nanocrystals (NCs) have emerged as a promising material for various applications due to their unique optoelectronic properties. Traditional fabrication methods for these NCs rely on colloidal chemistry, which can be time-consuming and may require complex purification steps. In this presentation, we will discuss the use of ultrafast laser processing as a versatile tool for the controlled modification of metal halide perovskite NCs. This technique offers several advantages, including rapid processing times, control over NC morphology, and the ability to conjugate NCs with 2D materials.

We will present our work on the laser-induced morphological and structural changes of cesium lead bromide nanocrystals. By varying the laser fluence and wavelength, we have achieved different transformations in these NCs, including exfoliation, fragmentation, and oriented attachment leading to the formation of nanoplatelets and nanosheets. These transformations are accompanied by partial or complete anion exchange, which can be controlled by the choice of solvent.

Furthermore, we will discuss our findings on the laser-assisted fabrication of metal halide perovskite-2D nanoconjugates. By irradiating a solution containing both perovskite NCs and graphene-based materials with femtosecond laser pulses, we have successfully decorated the 2D flakes with perovskite NCs without affecting their primary morphology. The density of anchored NCs can be finely tuned by adjusting the number of irradiation pulses, allowing for precise control over the properties of the resulting nanoconjugates.

Finally, we will present our latest research on the application of laser-processed perovskite-rGO conjugates as electrodes in Zn-ion capacitors. The laser-induced conjugation method enables the uniform distribution of perovskite NCs on reduced graphene oxide (rGO) sheets, resulting in enhanced electrochemical performance. The resulting electrodes exhibit high specific capacitance and excellent stability, demonstrating the potential of this approach for energy storage applications.

Overall, our work highlights the versatility of ultrafast laser processing as a powerful tool for the controlled synthesis and modification of metal halide perovskite nanocrystals. This technique offers a rapid and efficient route to fabricate perovskite-2D nanoconjugates with tailored properties, opening up new possibilities for their application in various fields, including optoelectronics, energy conversion, and energy storage.

The optimization of the perovskite solar cell has been considered one of the important technological challenges. Since the device can be developed through various combinations of materials and experimental conditions, efficient use of computational techniques for device optimization is highly demanded to overcome the problem of the so-called "combinatorial explosion" in experimental studies. In our laboratory, we are trying to collectively apply various computational tools in computer simulations and machine learning techniques. In this presentation, we will report on our recent trial to predict device characteristics of perovskite solar cells using machine learning and computer simulations. One challenge is predicting device performances such as photo conversion efficiency (PCE) from experimentally obtained cross-sectional scanning electron microscope (SEM) images. By applying convolutional neural network algorithms, we could have achieved moderate success in so-called image regression, in which SEM images are used as input to predict PCE. Another challenge is to discover an optimal material and device configuration through device simulation and machine learning (regression) modeling. In the presentation, we will discuss our computational method and tools with some predictive results toward optimizing the perovskite solar cell.

Hybrid perovskites are emerging as top contenders in the next generation of photovoltaics, yet their stability under operational conditions remains a significant challenge. Specifically, degradation occurs at the interface with charge transport layers in perovskite solar cells during operation.^[1] To address this, we explore using supramolecular interfacial modulators at the interface of charge-transport layers with the purpose of suppressing degradation without interfering with the photovoltaic performance.^[2,3] This included functionalised triarylamine-based modulators, which are known to form hole-transporting supramolecular stacks,^[2] as well as chiral P,M-(1-methylene-3-methyl-imidazolium)[6]helicene iodides, which could contribute to the charge transport through chiral-induced spin-selectivity (CISS) effects. These modulators were applied at the interface between the perovskite active layer and the hole-transporting material in conventional perovskite solar cells (Figure 1). We have investigated their impact on the structural characteristics and optoelectronic properties via a combination of techniques, including X-ray diffraction, UV-vis and both steady-state and time-resolved photoluminescence spectroscopy, complemented with the further analysis of photovoltaic devices. Our investigation challenges the role of chirality in perovskite photovoltaics and reveals the contribution to the improvement of operational stabilities without compromising device performance, offering promising new strategies for advancing perovskite photovoltaics.^[3]

Over the last decade, halide perovskites have undoubtedly become one of the most promising materials or set of materials for a plethora of optoelectronic applications. However most synthetic and thin film deposition and growth approaches currently employed are difficult to upscale.

In this talk I will discuss some simple and upscalable methods for halide perovskites:

In the first part, I will present solvent-free mechanochemical grinding by ball-milling as a way to obtain high-purity perovskite bulk and nano powders on a gram scale in a short time. Moreover I will show how thermal vacuum deposition allows for the transformation of this bulk powders into high quality thin films with excellent optoelectronic properties in a completely solvent-free approach.

In the second part of the talk, I will discuss a simple spray-coating deposition method based on commercial and cost-effective airbrush technology. This methodology employs pre-synthesized colloidal nanoinks formed by room-temperature, short-ligand-assisted reprecipitation route. Eventually, spray-coated films are employed in proof-of-concept photodetectors with significant responsivity.

For researchers, it's a long road from the idea to the published article. Producing great research results does not necessarily mean they will automatically be appreciated by the community. Choosing the right journal, convincing editors as well as reviewers, and making work visible to others are essential steps on the way to success.

In this tutorial talk, Dr. Anja Wecker, Editor in Chief of Advanced Optical Materials at WILEY, will give an insight into publishing opportunities in relevant journals and the related peer review process. She started as an editor 12 years ago and since then has worked for a number of journals within WILEY’s materials science portfolio, such as Advanced Materials, Advanced Functional Materials, Advanced Photonics Research, Laser & Photonics Reviews, and Small Methods. From an editorial perspective, she will provide some guidance on how to best pass peer review with a well-prepared submission and maximize success in scientific publishing.

Lead halide perovskite nanocrystals (LHP NCs) are an emerging class of light-emitting semiconductors owing to their remarkable optoelectronic properties such as their high photoluminescence quantum yield (PLQY), tunable emission across the visible spectrum emission, and facile synthesis, which make them excellent candidates in high-performance devices such as LED lights and photovoltaic devices. One of the most interesting features of halide perovskites in comparison to classical semiconductor materials is their high defect tolerance, I.e., the uncoordinated ions and surface dangling bonds results can only form states within or close to valance or conduction bands. However, chlorine-based perovskites possess low defect tolerance and thus the surface defects result in the formation of deep traps that significantly reduce their photoluminescence quantum yield (PLQY).¹ Consequently, the PLQY of as-synthesized Cl-perovskite NCs is much lower (1-5%) than Br or I-perovskite NCs (80-100%).

In this work, I will discuss a comprehensive study of post-synthetic surface passivation of CsPbCl₃ NCs with metal halides and molecular ligands to improve the PLQY of NCs. A large variety of ligands with different functional groups such as quaternary amines, sulfonates, and phosphonates were screened to study the enhancement of PLQY according to their binding ability to the NC surface. In addition, different metal halides are screened to fill surface vacancies and thus improve the PLQY. These studies revealed that the chloride vacancies are the main reason for the low PLQY of Cl-perovskite NCs. Furthermore, we demonstrated the direct synthesis of CsPbCl₃ NCs with relatively high PLQY using the strongly binding ligands obtained from the screening of post-synthetic ligand passivation. Our results not only provide an in-depth understanding of the type of trap states in CsPbCl₃ NCs but also unravel the ligand types for effective passivation of CsPbCl₃ NCs, thus offering a new avenue to synthesize high-quality luminescent NCs either by direct synthesis or post-synthetic passivation.

To realize the large-scale production and commercialization of perovskite solar cells, development of scalable and sustainable manufacturing processes is required. Various large-area deposition methods such as blade-coating, slot-die coating, spray-coating and ink-jet printing have been reported as viable options for perovskite solar cell fabrication [1], [2]. Gravure printing as a deposition method offers an appealing alternative due to the high processing speed and possibility for “patterning by deposition” [3].

In this work, the development and optimization of the rheological and corresponding optoelectrical properties of gravure printing inks are presented. The tuning of commercial tin-oxide (SnO₂) nanoparticle inks for electron transporting layers in a n-i-p architecture is described. Also, the optimization of the perovskite inks with variable polymer additives is specifically addressed. As the performance of the printed PCSs is improved with material, ink, and process tuning, so will the opportunities for system integration and exploitation. In this work, in addition to the perovskite solar cell developments, the recent achievements in variable applications where the integration of flexible perovskite devices is required, is introduced [4].

Developing highly sensitive X-ray detectors with high atomic-number elements is crucial for reducing dose rates in medical applications. An X-ray detector with high sensitivity can accurately and efficiently detect even small amounts of X-ray radiation and convert it into an electrical signal, effectively implying that smaller doses can be applied in X-ray instruments in the medical field. Traditional X-ray detector materials such as Si and CdTe suffer from disadvantages such as low-to-moderate atomic numbers, high thermal noise and crystal impurities, all negatively impacting the overall detector performance. Bismuth (Bi)-based materials offer significant advantages, including excellent stability and high atomic numbers, to name a few, making them highly interesting candidates for applications such as X-ray detection.¹ This study investigates fully inorganic compounds, such as Cs₂AgBiBr₆ and other fully inorganic materials, as well as hybrid organic-inorganic Bi-based materials.

Mechanosynthesis is showcased as an effective method for fabricating new materials with precise stoichiometries, with the possibility for swift upscaling.^2,3 We aim to explore mechanosynthesis for the targeted synthesis of Bi-based materials and then utilize these synthesized powders for different applications, such as X-ray detection. These materials were synthesized using, for instance, dry mechanochemical ball-milling under various reaction conditions. The study emphasizes the impact of different reaction conditions, material composition, additives, and post-treatment processes on the performance of the detectors.

X-ray diffraction (XRD) was utilized to analyze the structural properties and composition of the synthesized pellets. The performance of the detectors was evaluated by measuring their photocurrent response under X-ray illumination. Our results indicate that Bi-based materials significantly outperform conventional commercial X-ray detectors in terms of sensitivity and detection limit. Optimizing the mechanosynthesis reaction conditions and carefully selecting additives and post-treatments further enhances the properties and performance of the Bi-based detectors.

This research demonstrates that Bi-based perovskite-inspired materials, in both single-crystal and pellet forms, have significant potential as effective X-ray detectors. These findings pave the way for developing safer, more stable, and high-performance alternatives to current commercial X-ray detectors. Additionally, this work highlights mechanosynthesis as a swift and viable route for fabricating these materials, contributing to more environmentally friendly and commercially viable solutions, for instance, in photovoltaics, LEDs, and X-ray detection.

Colloidal heterostructures are nanoparticles composed of two materials connected at an interface, that can exhibit unique properties different from those of their individual components. When two materials with suitable band alignment are chosen, the resulting heterostructures can convert sunlight into electron – hole pairs, which are then separated by the electronic structure of the junction. This can efficiently inhibit recombination, making the photogenerated carriers available for exploitation in photocatalytic reactions.

Our recently reported CsPbX₃/Pb₄S₃X₂ heterostructures ^[1] (where X= Cl, Br, I) are a promising example of such architectures, where two semiconductors with different crystal structures are connected by an epitaxial interface. Notably, the composition of the two domains can be independently tuned by exploiting a combination of direct-synthesis protocols and post-synthetic halide exchanges, leveraging on the different halide mobility in the two domains.

In this work, we first employed a combination of absorption and ultraviolet photoelectron spectroscopy to explore the band alignment of CsPbX₃/Pb₄S₃X₂ heterostructures, which we can now synthesize on the 100 mg scale. Based on these results, we identified a potential application in the photocatalysis of biomass conversion, like the oxidation of 5-hydroxymethylfurfural ^[2],[3]. Unlike more popular processes like CO₂ reduction these reactions can take place in organic solvents, which are more compatible with metal halides, and still hold significant relevance thanks to the production of chemicals with added economical value.

So far, our preliminary tests demonstrate excellent in-operando stability, and show that heterostructures are significantly more active as photocatalysts than their individual constituting materials, which we attribute to the efficient carriers separation at the junction. These promising results pave the way to further photocatalysis studies, currently ongoing, and are a significant first step towards the real-world application of these complex yet fascinating heterostructures.

Lead halide perovskite (LHP) nanocrystals have recently attracted considerable attention as a promising class of materials for optoelectronic applications. Their ionic lattice and labile surface chemistry require new strategies in ligand development. Recently, a range of ligands have been developed that significantly improve the colloidal stability of LHP NCs. This was mainly achieved by using zwitterionic ligands. To drive further development of ligands for LHP NCs, we sought to rationalize the binding behavior of commonly used ligands. Our study shows that zwitterionic phosphocholine- and phosphoethanolamine-based ligands bind statically to the LHP NC surface and exhibit the highest stability. Sulfobetaine-based ligands offer a good balance between stability and binding dynamics. Several ammonium-based ligands exhibit high dynamics but often have insufficient stability due to their pH sensitivity or suboptimal binding to the A-site pockets.

In this work, we propose a new family of long-chain guanidinium-based ligands that, without compromising stability, provide dynamic binding to the surface of NCs and thus easily accessible active sites on the surface. A library of guanidinium-based ligands was synthesized and applied to LHP NCs of different sizes and compositions, such as CsPbBr₃, FAPbBr₃ and CsPbI₃. The new synthetic approach enables the preparation of LHP NCs with quantum yields of up to 95% in colloidal solutions and up to 80% in compact films. This combination of properties makes LHP NCs capped with guanidinium-based ligands very promising for photocatalytic applications.

Utilizing machine learning in developing perovskite solar cells significantly reduces the need for extensive experimental trials, saving time and resources. This approach enhances the efficiency of perovskite solar cells by enabling the prediction of optimal material combinations and processing conditions based on existing data, leading to improved performance and reduced material usage. This study uses Machine Learning (ML) techniques to optimize the performance of Perovskite Solar Cells (PSCs) by determining the ideal thickness of the electron transport layer and the best coating parameters for high Power Conversion Efficiency (PCE). ML models are trained on extensive experimental data to predict outcomes based on varying electron transport layer thicknesses and coating conditions. A key benefit of this method is its ability to reduce the number of experiments needed to find the optimal parameters in solar cell production. This study utilizes a device configuration of ITO/SnO₂/FAMAPbI₃/Spiro-OMeTAD/MoO₃/Ag. For optimizing the electron transport layer (SnO₂) thickness in PSCs, a database was created from a series of experimental studies on coating parameters and environmental conditions. Three ML algorithms, Random Forest (RF), eXtreme Gradient Boosting (XGBoost), and Category Gradient Boosting (CatBoost), were chosen to optimize PCE. Hyperparameter optimization was performed using Bayesian optimization. Root Mean Square Error (RMSE) and Pearson Correlation Coefficient (r) were the metrics used to evaluate the models. The best results were achieved with XGBoost, showing an RMSE of 0.455 and a Pearson coefficient of 0.958. Consequently, the highest PCE obtained from the experimental studies has been increased from 13.2% to 14.26% with an 8% improvement under the predicted conditions.

Perovskites are a class of materials with a distinctive crystal structure ABX3. They have
garnered significant attention as promising candidates for solar cell applications. These
materials, typically consisting of a hybrid organic-inorganic lead or tin halide-based
structure, offer exceptional light absorption, charge-carrier mobility, and tunable band
gaps. The ease of fabrication and potential for low-cost production, combined with rapidly
improving power conversion efficiencies that now rival traditional silicon-based solar cells,
underscore their potential in the photovoltaic industry. Challenges remain, particularly
concerning stability and toxicity. In our current study simple and hybrid perovskites and
their properties have been studied through machine learning (ML) models, density
functional theory (DFT) calculations, and synthesis. Addressing stability challenges, as a
first step we concentrated on lead containing organic-inorganic perovskites, trying to find
stable compositions, while the challenging toxicity is our next goal. We started with data
mining, then used 7 ML algorithms to predict band gap energies for generated perovskites
compositions. Based on the gathered data the best model for the prediction was chosen
Linear Regression model. Due to it’s band gap energy FAPbBr_1.125I_1.875 was chosen as one
of the best compositions for solar cell applications. The ML results were confirmed through
DFT calculations and experiments. Band gap energies were theoretically calculated
through DFT and hybrid methods. Hartree–Fock method is used for hybrid functionals. The
synthesis was implemented thought solvothermal method and the uniform thin films were
obtained trough spin coating.

Perovskite solar cells (PSCs) have achieved impressive power conversion efficiencies (PCE) of up to 26.1%,^[1] however their commercialization is hindered by significant stability challenges, particularly in the presence of oxygen/moisture, and under operating conditions such as voltage bias, light exposure, and temperature fluctuations. These issues are often associated with migration of ions, which can lead to a degradation of optoelectronic properties, and, in turn can adversely affect both the performance and long-term stability of PSCs. Inherent defects and grain boundaries are the main ion migration pathways within the perovskite layer. Notably, unreacted lead iodide (PbI₂) at these sites, including surface of perovskite grains, and the interface between the perovskite layer and the charge transport layer, is a major cause of intrinsic instability under illumination. PbI₂ can break down into iodine and metallic lead, acting as recombination centers, further promoting ion migration, and accelerating degradation.^[2] In stark contrast for the operation of PSCs, it has been shown that enhancing device performance often involves adding a small excess of PbI₂ to the precursor solution.

The conflicting observations that PbI₂ can both enhance performance but also degrade stability suggests a need for research efforts directed toward simultaneously mitigating crystallization of residual PbI₂ while improving device stability, ensuring that efficiency gains do not compromise the long-term reliability of perovskite solar cells.

This presentation addresses these challenges through supramolecular complex engineering by introducing beta-cyclodextrin (β-CD) into a triple cation perovskite layers to effectively prevent the crystallization of residual PbI₂. This approach results in uniform crystal growth and the passivation of undercoordinated lead cation defects, as confirmed by XRD and SEM analyses. The use of β-CD leads to a PSC with an improved PCE of 21.36%, surpassing the control (19.4%), and enhanced stability against aggressive thermal stress and high humidity (85% RH), likely attributed to defect passivation as evidenced by PL, SCLC and the dependence of V_OC on the incident light intensity studies. Notably, in comparison to the β-CD-free control, the β-CD-treated sample exhibited minimal optical bandgap shifts of 3 meV after 1170 hours of moisture exposure. In addition, the devices treated with a 0.5% of β-CD showcased improved stability, maintaining over 73% of their initial PCE even after undergoing 320 hours of testing at 50-60℃. XPS and NMR observations reveal that β-CD effectively anchors uncoordinated Pb²⁺ ions, preventing the formation of metallic Pb and enhancing film stability under environmental stress. Furthermore, this method not only passivates unreacted PbI₂ but also provides valuable insights into the role of β-CD in PSCs. Additional tests with Maltose as a non-cyclic control were conducted and confirm the superior ability of β-CD to enhance perovskite film stability under harsh conditions.^[3] The formation of a supramolecular system between β-CD and perovskite holds promise as a strategy to control perovskite precursor chemistry, material structure, and subsequent device performance and stability.

Energy-harvesting materials are currently on the rise, as solar energy provides the Earth with a considerable amount of energy.[1] Designing hybrids that harness the synergistic power of both systems is of great significance in such a context. Hence, the use of nanohybrids based on perovskite nanocrystals and photoactive organic molecules such as BODIPY dyes triggers the properties of wide and strong light absorption in the visible range and the generation of reactive species such as triplet excited states, respectively, which could potentially be used for organic photocatalysis.[2] In this contribution, we investigated the photophysical properties of nanocrystal-organic nanohybrids at the interface. For this end, CsPbBr₃ perovskite nanocrystals (NCs) have been merged with BODIPY dyes, specifically 8-(4-carboxyphenyl)-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BDP) and 8-(4-carboxyphenyl)-2,6-diiodo-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (I2-BDP). Through the use of steady-state and time-resolved absorption and photoluminescence techniques, we unveiled the sensitization mechanism of BODIPY dyes in the corresponding nanohybrids by selective excitation of the NCs. Spectroelectrochemical analysis and theoretical calculations confirm the generation of transient intermediate species, which are found to be crucial in the photosensitization mechanism. The efficient generation of triplet reactive species in I2-BDP allows the NC@I2-BDP nanohybrid to be used as a potential photocatalyst for the oxidation of α-terpinene to ascaridole via singlet oxygen formation.[3]

Tuning the crystallinity, stability, and optoelectronic properties of tin halide perovskite-based semiconductors is crucial for advancing these promising materials toward practical device applications. Embedding organic semiconductor cations within the layered structure of tin perovskites can offer an effective means to attenuate the dielectric and quantum confinement effects by enabling the charge transfer between the organic and inorganic layers. However, incorporating bulky pi-conjugated organic semiconductor cations in layered perovskites is a challenge. Herein we leverage our previously demonstrated molecular engineering strategy^[1] to afford the incorporation of napththalene diimmide (NDI) cations with alkyl chain lengths of 6 carbons into two-dimensional (2D) tin halide perovskites that show enhanced electron mobility and air stability. We show the importance of both cation molecular structure and processing conditions in obtaining high quality thin films. Additionally, we discuss the role of additives in facilitating the formation of quasi-2D tin halide perovskites with enhanced crystallinity and elucidate the importance of the additive molecular structure—suggesting this strategy can generally advance the structural qualities of solution-processed perovskite materials, and consequently enhance device performance and stability.

Bifaciality is a salient sub-field for perovskite solar cells (PSCs), both due to reaching higher efficiency values for single-junction devices and applying them to tandem devices with other technologies or PSCs [1]. For this purpose, transparent electrodes (TEs) have been investigated, including TCOs, metal nanowires, ultrathin films, and 2D materials such as graphene [2]. TEs with noteworthy bendability properties are also riveting to be used in lightweight-flexible devices for novel areas like portable devices or aerospace applications [3]. In this context, we present bifacial perovskite solar cells, suggesting alternative transparent electrodes composed of three ultrathin layers, called OMOs (oxide-metal-oxide). The main material of the study is nickel oxide/silver/nickel oxide (NAN) [4] layers where a silver layer is sandwiched between NiO films, with thicknesses of 35 and 8, for NiO and Ag layers respectively. The triple layers are fabricated with sequential e-beam deposition, consisting of only one evacuation process. A comprehensive characterization of NAN layers providing the transmittance and conductivity properties and their performance when applied to perovskite solar cells, with remarkable Voc of 1.11 V using an active layer bandgap of 1.6 eV, will be presented in which the charge transport and absorber layers of the devices are fabricated via solution-based methods on rigid and flexible substrates.

Halide perovskite solar cells have revolutionized the photovoltaic field in the last decade. In a decade of intensive research it has been a huge improvement in the performance of these devices, however, the two main drawbacks of this system, the use of hazardous Pb and the long term stability, still to be open questions that have not been fully addressed. Sn-based perovskite is the most obvious alternative to Pb, producing degradation materials less toxic and presenting the highest performance among the different Pb-free halide perovskites, but presenting a lower stability than their Pb-containing counterparts. In this talk, we highlight how the use of proper additives and light soaking for defect engineering can increase significantly the stability of formamidinium tin iodide (FASnI3) solar cells, and discuss about the different mechanism affecting this stability, beyond the oxidation of Sn2+, and how they can be countered, analyzing specially the light soaking treatment. In addition, we report alternative ways to prepare 2D Sn-perovskite powders, that can be used as precursors for fabrication of Sn-based LEDs or as by themselves to drive photocatalytical reactions. We will discuss on the rational design of halide perovskites containing non-critical raw materials towards photoelectrochemical processes, and the importance of extracting basic electronic and optical information to understand the carrier dynamics to maximize the performance and stability of these materials. Moreover, proper interrogation tools are needed to validate their photo(electro)catalytic activity and selectivity.

Metal-halide perovskites exhibit bright and sharp luminescence, with properties that can be tuned over a wide range through solution processing. The first half of this talk examines realising polarised luminescence. Here, CsPbI3 nanoplatelets are self-assembled into an edge-up orientation. Through strong dielectric and quantum confinement, there is a large exciton fine structure splitting. As a result, we achieve strong emission from out-of-plane dipoles for the optically bright excitons in these superlattices. In light-emitting diodes, this leads to a high degree of polarisation of 74.4% in electroluminescence, without requiring any photonic structures [1].

The second half of this talk makes use of the versatility of metal-halide perovskites to examine hot carrier cooling [2]. In particular, although defect tolerance has been widely quoted as a key enabling properties of band-edge (cold) carriers, it is unknown whether this can be extended to hot carriers. Through interband and intraband femtosecond spectroscopy, along with excitation-energy-dependent photoluminescence quantum efficiency measurements and kinetic modelling, we show that hot carriers are not universally defect tolerant, but depend on the energy of the traps. The trap density in CsPbX3 (X is Br, I or both) is intentionally tuned by washing the surface with polar antisolvents [3], and we show that hot carriers are directly trapped by defects, without going through a cold carrier intermediate. By showing how defects affect hot carriers, this work leads to design principles that could be used to realise hot carrier solar cells.

Metal halide perovskites (MHPs) exploitation represents the next big frontier in photovoltaic technology with power conversion efficiencies above 26 %. However, two main drawbacks limit the potential application and commercialization of the technology: toxicity, due to the presence of lead, and instability under moisture, light and temperature, among other factors.  Currently, research efforts are dedicated to the synthesis of novel Pb-free MHPs with elements such as tin (Sn), germanium (Ge), bismuth (Bi), Titanium (Ti) or antimony (Sb) as substitutes for lead (Pb). Although the tin-based perovskite solar cell is the most promising candidate, other promising PSCs with elements such as Bi (with current efficiencies around 5 %) are being highly studied. Among the different approaches employed to boost the stability of halide perovskite solar cells, A-site substitution using organic ligands, has been the centre of research worldwide. In lead perovskite solar cells, A-site substitution with various organic and inorganic materials has been commonly explored to control the optoelectronic properties and consequently improve device performance. Cations such as methylammonium (MA+), formamidinium (FA+), phenethylammonium (PEA+), ethane- 1,2-diammonium (EDA+), and guanidinium (GA+) ions have shown positive outcomes when used at optimized stoichiometries in perovskite solar cell devices. Recently, a novel A-site cation, dimethylammonium (DMA+) cation, has been introduced in Pb-containing perovskite solar cells, which enhanced the photovoltaic performance and device stability. DMA can act as an A-site cation to incorporate with CsPbI3, creating a hybrid perovskite of CsxDMA1-xPbI3, which is more stable in ambient conditions than pure CsPbI3. This enhancement in stability is also observed when partial substitution of the large dimethylammonium (DMA) cation at the A site of FAxCs1–xPbIyBr3–y perovskites, results in a bandgap increase and it is accompanied by an expansion of the crystal lattice. The solar cells resulted extremely stable, retaining 96% of their original efficiency over 2200 h at 85 °C in the dark and 92% of their original efficiency after operation at 60 °C for 500 h. It is particularly noteworthy the high stability and hydrophobicity of DMASnX3 and PEA2SnX4, the Pb-free MHP do not dissolve in water, but it rather remains dispersed in solution, maintaining unchanged the crystal structure and the optical properties. The latter makes this perovskite an interesting candidate as photocatalyst. In this presentation, I will show our most recent results on the synthesis of Pb-based and Pb-free halide perovskites and their application as solar cells and potential photo(electro)catalyst. The materials were fabricated as heterojunctions with MXene thin films.

Quaternary Mixed-Metal Chalcohalides (MMCs), composed of Group IV and V elements such as Pb, Sn, Bi, and Sb, along with halide and chalcogenide ions, are an emerging class of perovskite-inspired ns² semiconductors (1). These materials possess promising optical and electronic properties, which are due to two key features: the presence of two ns² cations and spontaneous polarization. These result in a lower probability of carrier capture (2,3). While these materials are highly desirable for various applications in energy conversion and storage devices, their potential use may be limited by the challenges associated with synthesizing chalcohalide thin films. For instance, they often require non-solution methods or multi-step processes (1,4).

In my presentation, I will discuss our most recent research on MMCs. The initial portion of my talk will focus on the single-step, solution-based fabrication and the characterization of Pb-Sb-S-I and Sn-Sb-S-I MMC compositions. I will also highlight the impressive stability of these MMC compositions, both in terms of material and device performance under ambient air, humidity, and operation. Towards the end, I will present some of our preliminary findings related to the light-harvesting capabilities of these MMCs.

Most semiconductor technologies rely on the intentional engineering of charge transport. In the case of halide perovskites — a semiconductor class currently developed for critical components in solar cells and light-emitting devices —reliable control of their charge transport is still needed. Such advances may help improve the performance of these semiconductors in current applications and open myriad new possibilities. In this talk, I will describe two routes to enhance the conductivity of halide perovskites. We first describe how introducing charge reservoirs inside expanded analogs of halide perovskites allows controlling their electrical doping.¹ Secondly, we describe how mixed-valence in halide perovskite can be harnessed to enhance conductivity.²

References

1) Matheu, R.; Ke, F.; Breidenbach, A.; Wolf, N. R.; Lee, Y.; Liu, Z.; Leppert, L.; Lin,Y.; Karunadasa, H. I. Charge Reservoirs in an Expanded Halide Perovskite Analog:Enhancing High-Pressure Conductivity through Redox-Active Molecules. Angew. Chemie Int. Ed. 2022, 61, e202202911.

2) Li, J.; Matheu, R.; Ke, F.; Liu, Z.; Lin, Y.; Karunadasa, H. I. Mosaic CuI−CuII−InIII 2D Perovskites: Pressure-Dependence of the Intervalence Charge Transfer and a Mechanochemical Alloying Method. Angew. Chemie Int. Ed. 2023, 62, e202300957.

Halide perovskite semiconductors can merge the highly efficient operational principles of conventional inorganic semiconductors with the low‑temperature solution processability of emerging organic and hybrid materials, offering a promising route towards cheaply generating electricity as well as light. Following a surge of interest in this class of materials, research on halide perovskite nanocrystals (NCs) has gathered momentum in the last decade. This talk will highlight several findings of our group on their synthesis, for example our recent study on the influence of various exogenous cations and acid-based equilibria on the growth of NCs, and the preparation of NCs in the strong quantum confinement regime. Our group is pioneering syntheses of NC heterostructures in which a perovskite domain is interfaced either with a metal chalcogenide or a chalcohalide. This talk will discuss how we can computationally predict the feasibility of such heterostructures, based on interfacial matching. We will also overview selective anion/cation exchange reactions that can take place on a starting heterostructure, from which a series of second-generation heterostructures can be generated. 

In two-dimensional hybrid organic-inorganic metal halide perovskites (2D-HOIPs), the stacking setting of the adjacent inorganic sheets is influenced by the nature of the incorporated organic cation. [1-2] The photophysical properties of 2D-HOIPs can be accordingly tuned. However, the structural properties of 2D-HOIPs are more complex than the parent 2D metal oxide perovskites because of the larger size of the organic cations, their different chemical and structural properties. For instance, an order-disorder transition of the cation may result to a ferroelectric phase, [3] while octahedral distortion can modulate photophysical and electrical properties of the HOIP. [4] In this context, octahedral distortion as well as cation’s distortion urges for a systematic understanding of the crystallographic properties of 2D-HOIPs. [5]

In recent years, implementation of iodine-terminated alkylammonium cations is attracting a lot of interest, since it has been proposed that the development of halogen-halogen supramolecular interactions between the iodine atom of the organic cation (acting as halogen bond, XB, donor) and the apical inorganic iodine atoms of the inorganic sheets (acting as halogen bond, XB, acceptors) suppress phase transitions towards undesired lower-symmetry phases. [6] The rich halogen chemistry of metal halide perovskite semiconductors brings such halogen bond (XB) strategies under the spotlight, [7] while halogen-halogen interactions, in general, may lead also to unprecedented properties. [8] Herein, a bimodal iodine-terminated alkylammonium cation has been studied as a supramolecular modulator of the crystalline organization of a 2D-HOIP. Utilizing heat as an external stimulus a controlled and reversible single crystal-to-single-crystal phase transition was observed. Controlling the conformation of the cation, the modulation of the interlayer XB formation was achieved. The new perovskite phase has discrete structural and photophysical properties, as evidenced by variable temperature investigation by single-crystal X-ray diffraction, solid-state NMR, UV-Vis and photoluminescence spectroscopies.

Halide perovskite materials have garnered significant attention for their potential in diverse applications such as solar cells, photodetectors, lasers and photocatalysis. CsPbBr₃, an all-inorganic metal halide perovskite, exemplifies this potential with its impressive stability against moisture and light [1]. With a direct band gap of 2.3 eV, large atomic number and high light-electron conversion efficiency, CsPbBr₃ is particularly suitable for high-energy radiation detection [2]. The material’s versatility extends to photovoltaics [3] and multicolour LEDs [4] through partial or total substitution of the bromide anion with iodide and/ or chloride. Device performance in polycrystalline films, which are typically produced via solution-based or vapour deposition methods, is greatly affected by the density of grain boundaries. In general a negative effect is attributed to grain boundaries due to an increased number of recombination sites, pathways for ion migration and openings for perovskite degrading species like oxygen [5]. Conversely, Luchkin et al. reports grain boundaries to be the primary location for photocarrier generation and transport, which can enhance device performance [6]. Therefore, controlling the deposition process to manage grain morphology and relating to the film performance is essential for the device optimization.   

In this study, we employ the hardly explored close space sublimation (CSS), a fast and scalable physical vapour deposition technique, to fabricate polycrystalline CsPbBr3 films [7]. Understanding the growth of CsPbBr₃ can serve as a model for other perovskite materials, contributing to advancements in thin film solar cells and light emitting applications. This solvent free synthesis route enables rapid growth rates up to 6 µm/min with a high material utilization of 98%. Single-phase CsPbBr₃ films are achieved across a wide range of deposition parameters. By separately adjusting the deposition conditions (substrate and source temperature, pressure), we access different growth regimes, enabling tunable grain sizes in the films without additional treatment.

Our study focuses on characterizing films with thicknesses of 1 – 10 µm and varying grain sizes. Using electrical and optical characterization methods like current – voltage characteristics, conductive atomic force microscopy, scanning electron microscopy, Raman and photoluminescence spectroscopy we correlate the optoelectronic properties with film morphology and grain structure. Taking advantage of the grain tunability offered by CSS, we aim at exploring the effect of grain size on the optoelectronic properties of CsPbBr₃, which is crucial for the optimization of perovskite-based device performances.

Over the last ten years, the role of hybrid metal halide perovskites has received significant attention as suitable materials for various electronic applications. Indeed, their outstanding optoelectronic properties such as high-power conversion efficiency, tunable bandgap, and high absorption coefficient, make them suited for several applications in different devices as photovoltaic cells, photodetectors, light emitting diodes, and sensors [2]. Starting from the hybrid organic-inorganic perovskites (HOIPs), the introduction of a chiral molecule as organic cation leads to the breaking of the spatial inversion symmetry, allowing new possible designs based on the combination of polarity and chirality [1,3].  In the scientific scene, this opened plenty of novel applications provided by outstanding chiroptical properties, such as circular dichroism, circular polarized emission, chiral induced spin selectivity and so on. To extend the actual knowledge of these chiral systems, it is important to investigate those parameters which have a major impact on the chirality transfer mechanism, with the final aim to unveil it. From a material chemistry point of view this involve an important work on materials’ structure, involving several modulations/substitutions on the latter. More specifically, in this contribution we will present the results of the role of the central metal, showing the modulation of the optoelectronic properties with two different metals. Firstly, we prepare an initial series of novel chiral metal halide maintaining the chiral cation (4-Chlorophenyl)ethylenimine (Cl-MBA), accompanied by different central metal, namely Pb, Sn and Ge. This approach brought to the discovery of (R/S/rac-ClMBA)₂SnI₄ and (R/S/rac-ClMBA)₂GeI₄ compositions, and to another interesting Ge-containing 1D system, namely (R/S/rac-ClMBA)₃GeI_5. The work provides a comparison not only in terms of structural features and chiroptical properties but also in terms of computational modelling, which helps us to deeply understating the role of central cation and the difference in terms of efficiency moving from a Pb-based perovskites to a Pb-free one. Final aim of this work is to unveil the impact of chemical degrees of freedom on the chirality transfer between the organic cation and the inorganic framework to provide tuning strategies for materials engineering.

The structural and thermodynamic stability of pure FAPbI3 perovskite films has been a topic of extensive research and discussion in the field of perovskite solar cells. While previous studies have primarily focused on the transition of X-ray diffraction (XRD) patterns from an α-FAPbI3 cubic phase to the more stable delta phases, our research takes a novel approach. We present a comprehensive structural and symmetry analysis that uncovers the tetragonal nature of the perovskite FAPI phases processed with Flash IR annealing (FIRA), offering a fresh perspective on this intriguing subject.

In phase transformation and crystallization, the film's crystal structure might be affected by the strain field, especially if the film undergoes structural distortions or tilting of lattice planes. Therefore, by controlling the FIRA process parameters (such as temperature and heat rate), it is possible to finely tune the properties of the film, including strain-related properties, as shown. [1] These processes lead to highly stable perovskite devices, where we further show that molecular additives contribute more to the crystallization dynamics as a mass transport diffusion process than to the atomic defect level. We also present a new methodology based on large dataset computational image processing correlated with advanced characterization techniques.

Operando Perovskite Interface Characterization using Photoemission Spectroscopy To enhance and refine perovskite optoelectronic devices, understanding the atomic and electronic structures of perovskite material interfaces is essential. X-ray-based spectroscopies, including photoelectron spectroscopy and X-ray absorption spectroscopy, provide element-specific, non-destructive chemical and electronic structure insights at the atomic level. With recent advancements at synchrotron facilities and methodologies developed by our team and others, these tools are rapidly advancing for energy material system studies. [1-3] They facilitate the examination of interface chemistry, energy alignment, valence and conduction band properties, and charge dynamics. In this presentation, we share our latest results using X-ray absorption spectroscopy and energy-dependent photoelectron spectroscopy on perovskite interfaces. Our research covers single crystal surfaces and interfaces to functional device structures. We illustrate how to analyze interface chemistry and determine energy alignment in perovskite/hole-conductor/metal interfaces, both in the dark and under visible light. Specifically, we will discuss operando measurements using hard X-ray photoelectron spectroscopy.

References:
1. Svanström, S et al ACS Appl. Mater. Interfaces 15, 12485–12494 (2023).
2. Man, G. J. et al. Phys. Rev. B 2021, 104, L041302

3. Garcia-Fernandez, A. et al., SMALL 2022, 18, 2106450

The integration of plasmonic nanoparticles into perovskite-based optoelectronic devices represents a promising frontier in enhancing device efficiency for both light-emitting diodes (PeLEDs) and solar cells (PSCs). Perovskite materials, known for their large absorption, long diffusion lengths, tunable bandgap, high quantum yield, and narrow emission bandwidths, are ideal candidates for next-generation optoelectronic applications. Despite these advantages, PeLEDs still face challenges in optimizing quantum yield, color purity, and angular control. Similarly, PSCs, specifically tandem solar cells with narrow bandgap perovskites, suffer from limited absorption capacities, hindering their potential efficiency.

Through rigorous simulation design and experimental synthesis, our research demonstrates that embedding plasmonic nanoparticles randomly distributed within these perovskite structures can significantly enhance their photophysical properties. By optimizing parameters such as metal type (Ag, Au, Cu), shape, and volume filling concentration, we establish guidelines for the future development of plasmonic resonance-based optoelectronic devices [1-3].

Specifically, we achieve a three-fold enhancement in the integrated emission of thin CsPbBr3 films by incorporating precisely engineered spherical Ag nanoparticles, allowing for controllable directionality in the forward direction or at desired larger angles. Similarly, we demonstrate that, through rigorous design, it is possible to provide a realistic prediction of the magnitude of the absorption enhancement that can be reached for perovskite films embedding metal particles. In all-perovskite tandem solar cells, we maximize light harvesting while minimizing parasitic absorption, providing an absolute power conversion efficiency enhancement of 2% in Sn-based perovskite compositions through synergistic near- and far-field plasmonic effects [4]. This approach allows for thinner perovskite films, facilitating photocarrier collection and reducing the amount of potentially toxic lead in the devices.

Our findings underscore the transformative potential of plasmonic nanoparticles in enhancing the efficiency of perovskite-based optoelectronic devices, paving the way for advanced applications in lighting, displays, and renewable energy solutions.

Photocatalysis has emerged as a highly valuable and economic method that was used extensively in the last few decades for the synthesis of important organic molecules and facilitating crucial bond formations such as C-C, C-N, and C-O bonds.[1-3] Although significant development has been made in the field, conventional photocatalysts usually comprise expensive transition metals such as Ru[4], Ir[5], or Au[6], and are often hard-to-prepare, require air-free conditions for obtaining high conversion rates, and may be of limited reusability. A promising alternative for solar- or LED-driven photocatalysis lies in lead halide perovskite quantum dots (LHP-QD) as recent developments highlighted their strong and broadly tunable absorption with high coefficients (~10⁶ M^-1cm^-1), near unity quantum yields (>90%)[7], highly dynamic and accessible surface, and low electron-hole binding energy causing facile charge generation/transfer. These properties overall indicate the high potential of lead halide perovskites as sustainable heterogeneous photocatalysts.   

In this work, we showcase the use of LHP-QDs as efficient photocatalysts in various organic transformations. First, we demonstrate the impact of designer ligands on the catalytic activity at extremely low catalyst loadings (<10*10^-6 mol%, <100 ppb) for α-, and γ- bromination of the β-ketoesters, ketones, and various benzyl derivatives reaching turnover numbers over 9,000,000. Investigating the effect of solvent on the performance as well as doing a comprehensive mechanistic study allowed us to rationalize the catalyst properties. Next, we show the development of thin-inorganic coatings (AlO_x, TiO_x, and ZrO_x) on LHP QDs for efficient photocatalysis. We explore the dimerization of benzyl bromide derivatives as model systems using surface-engineered LHP-QDs, achieving high conversions to the desired products in short reaction times (<4h) and with low catalyst loadings. Our findings confirm that a properly designed surface passivation and balancing of the oxidation and reduction reaction rates can successfully resolve the stability issues anticipated for such ionic compounds in reaction conditions. Photocatalysts can be separated from the reaction mixture, regenerated, and still exhibit >95% conversion efficiency during the second cycle of the reaction.

Overall, our efforts reveal that LHP QDs enable photocatalyzed transformations that are otherwise not achievable with the established photocatalysts, and we believe the engineering of the surface in these materials will allow the community to advance in the context of photoredox catalysis.

Vacuum deposition emerges as a pivotal method for scaling up perovskite solar cells (PSCs) in commercial applications, offering conformal coatings on various surfaces and precise layer control, aligning with large-scale manufacturing needs. Atmospheric conditions, particularly moisture, significantly impacts perovskite layer quality, requiring controlled environments. Through in-situ grazing incidence wide angle X-ray scattering (GIWAXS) and 3D time of flight secondary ion mass spectroscopy (ToF-SIMS) we show that annealing in the presence of humidity, is essential for the interdiffusion of inorganic and organic precursors necessary to achieve high quality thermally evaporated perovskite absorbers via sequential deposition. Notably, spectroscopy measurements also indicate high non-radiative bulk recombination in the absorbers photoluminescence when processed in the absence of relative humidity, bolstering the importance of interdiffusion for the device's overall performance. This has resulted in the development of high-performance p-i-n perovskite solar cells (PSCs) exclusively processed through vacuum techniques, achieving an impressive power conversion efficiency of 20.45%. Stability tests reveal an initial burn-in phase during accelerated aging at 85°C and 1 sun illumination using full spectrum while holding the device at the open-circuit condition. Despite this phenomenon, the devices exhibit remarkable stability, remaining functional for additional 500 hours post the initial challenge. This finding highlights the resilience and potential durability of the newly developed vacuum-processed PSCs, marking a significant advancement in the field of perovskite solar cell technology.

Modern color image sensors and cameras face challenges in improving sensitivity and color fidelity due to the inherent inefficiencies in light utilization. A major factor contributing to these inefficiencies is the use of passive optical filters, which absorb a significant portion of incoming light, thereby diminishing the sensors' quantum efficiency. We present an innovative architecture for color detector arrays, leveraging multilayer monolithically stacked lead halide perovskite thin-film photodetectors. By utilizing the tunable bandgap of perovskites, we selectively absorb the red, green, and blue regions of the visible light spectrum, eliminating the need for traditional color filters. We achieved external quantum efficiencies of 50%, 47%, and 53% for the red, green, and blue channels and color accuracy of 4.5ΔE_Lab, outperforming state-of-the-art color-filter array and Foveon-type photosensors while avoiding demosaicing artifacts. Our study lays the groundwork for the next generation of image sensors, employing conceptually novel architectures with enhanced light utilization.

The recent surge in interest towards antimony- and bismuth-based perovskite-inspired materials (PIMs) is attributed to their potential as sustainable and air-stable absorbers for photovoltaic applications.^[1]

Lately, we have presented the first 2D triple-cation antimony-based PIM (CsMAFA-Sb),^[2] which incorporates inorganic cesium alloyed with organic methylammonium (MA) and formamidinium (FA) cations at the A-site of the A₃Sb₂X₉ structure. The inclusion of the hybrid A-site cations proved to be crucial in reducing trap-assisted recombination pathways, thereby enhancing the performance of both outdoor and indoor photovoltaics. Furthermore, through a careful doping engineering of the hole-transport layer, the devices remained stable after nearly 150 days of storage in dry air.

While promising shelf-lifetimes of PIM-based photovoltaics have been often reported, the operational stability of the devices remains so far largely overlooked. To address this, we have incorporated Bi(III) ions into the CsMAFA-Sb structure while at the same time introducing dimethyl sulfoxide (DMSO) into the solvent system of the precursor solution. This resulted in a novel PIM, CsMAFA-Sb:Bi, with enhanced film morphology and large crystalline domain size. The corresponding photovoltaics have demonstrated a slightly increased power conversion efficiency (PCE) and significant improvements in the stability under operational conditions at the Maximum Power Point (MPP) compared to the control devices based on CsMAFA-Sb. Remarkably, under a constant 0.1-Sun illumination at the MPP for over 100 hours, the CsMAFA-Sb:Bi devices not only sustained the initial PCE, but even witnessed an over 10% PCE increase. Under constant 1-Sun MPP for over 100 hours, the CsMAFA-Sb:Bi devices still retained over 75% of the initial PCE. The stability enhancement is attributed to the reduced ion migration upon Sb:Bi co-alloying. Our findings represent the most extensive stability study reported for PIM-based photovoltaics to date, which demonstrates their potential for commercial applications.

The request for sustainable and renewable energy sources has motivated a significant shift toward innovative methods for producing and storing clean energy through green solar fuels. Photocatalytically active heterojunctions based on metal halide perovskites (MHPs) are drawing important interest for their tuneable ability to promote several redox reactions. This study investigates two composite systems: a classic double perovskite-based, Cs₂AgBiCl₆/g-C₃N₄,¹ and a vacancy-ordered perovskite-based, Cs₂SnBr₆/g-C₃N₄. The first system has been studied and employed for both solar-driven hydrogen generation from chloride media and nitrogen reduction and the second one for nitrogen reduction. The efficiency of the Cs₂AgBiCl₆/g-C₃N₄ system depends on the relative amounts of perovskite and carbon nitride to promote the two reactions. Spectroscopic investigations and density functional theory (DFT) modelling reveal that perovskite halide vacancies are primary reactive sites for hydrogen generation and can be, together with g-C₃N₄ nitrogen vacancies crucial also for nitrogen reduction.¹ On these bases, again through a combined experimental and computational approach, we provide a detailed framework of the mechanism supporting the efficient nitrogen reduction reaction to ammonia observed in Cs₂SnBr₆/g-C₃N₄ system. The vacancy-ordered perovskite is characterized by a higher surface density of halide vacancies than the double perovskite and then the Cs₂SnBr₆/g-C₃N₄ system achieves the highest ammonia evolution rate of 266 μmol g^-1 h^-1. Photoluminescence studies and differential transmission measurements stress the importance of compositional engineering in enhancing photocatalysis efficiency for both reactions. This work represents a significant advancement in photocatalytic green fuels production, especially in the field of nitrogen photofixation, proposing materials and structures that can potentially improve sustainable ammonia production, thereby contributing to energy independence and reduced carbon emissions.

Perovskite solar cells (PCSc) have emerged as a highly promising photovoltaic technology due to their cost effective fabrication processes and remarkable power conversion efficiencies. In 2009, PSCs were initially proposed as visible light sensitisers for photovoltaics, with 3.8% power conversion efficiency (PCE) at the laboratory scale to date, reaching an extraordinary 26.1%. However, the environmental and health concerns are associated with lead (Pb) in high performing PCSs. Tin perovskite solar cells (Sn-PSCs) are considered as eco friendly alternatives to Pb based PSCs. Ploy (3,4-ethylenedioxythiophene) polystyrene sulphonic acid (PEDOT.PSS) as hole transport layer (HTL) and dimethyl sulfoxide (DMSO) employed for Sn-PCSs approaching 15% but they are leading towards fast Sn oxidisations. Here we presented the PEDOT.SS and DMSO free compositions FA_0.95EDAI_0.05SnI₃ in p-i-n structure for Sn-PSCs. The perovskite film achieved good morphology using ploy (3,4-ethylenedioxythiophene) as HTL along with Al₂O₃ nanoparticles as inter layer in a DMSO-free solvent system. The fabricated device achieved a remarkable PCE of 8.72 % under simulated AM 1.5G illumination.

Halide perovskites have emerged as promising materials for optoelectronic devices due to their exceptional optoelectronic properties. These materials have found many applications such as light-emitting diodes, photodetectors, lasers, and solar cells[1–6]. Among them, inorganic halide perovskites CsPb₂Br₅, CsPbBr₃, as well as dual-phase perovskites, are particularly promising. However, achieving the formation of thin films by simple and scalable fabrication methods under ambient conditions with low temperature deposition remains a challenge.

Traditional techniques like spin-coating[1], vapor deposition [7], thermal vacuum deposition [8] or electrospining [9] are difficult to upscale and often require inert atmospheres or high temperatures, limiting their practicality. We address this challenge by developing a simple approach for the fabrication of CsPbBr₃ and CsPb₂Br₅ nanocrystals inks at room temperature, which are then used for the one-step deposition of thin films, using readily available commercial airbrush technology.

This approach offers significant advantages in scalability compared to existing techniques. We demonstrated the deposition of thin films with tunable properties from these nanoinks by a scalable spray-coting process using a simple commercial airbrush under near-ambient conditions. The nanoinks were placed in the airbrush cup, a nitrogen gas flow with a pressure of 0.4 bar was used, and the flow was controlled through nozzle opening. The substrates were heated on a hot plate to allow for instant solvent evaporation.

We investigated the effects of deposition temperature and the number of deposited layers. We observed crystallographic differences with increasing temperature. At room temperature, we obtained phase-pure orthorhombic CsPbBr₃ and tetragonal CsPb₂Br₅. At higher deposition temperatures, traces of PbBr₂ were observed alongside CsPb₂Br₅ using the CsPb₂Br₅ nanoink. Additionally, CsPbBr₃ nanoink deposited at higher temperature exhibited the presence of a dual-phase CsPbBr₃/ CsPb₂Br₅. The optical properties were studied. We noticed similar photoluminescence for all conditions with an emission peak centered around 520 nm characteristic of this perovskite and as has already been noted by others [10-13].

Eventually, we considered the photocurrent properties of the spray-coated films. With optimized deposition parameters, the photoresponse under different lighting conditions (white light and monochromatic light) shows up to four orders of magnitude differences between photocurrent and dark current for dual-phase CsPb₂Br₅/CsPbBr₃ thin films.

Halide perovskite nanocrystals are promising materials for optoelectronic applications. Metal doping provides an avenue to boost their performance further, e.g., by enhancing light emission, or to provide additional functionalities, such as nano-scale magnetism and polarisation control. However, the synthesis of widely size-tuneable nanocrystals with controlled doping levels has been inaccessible using traditional hot injection synthesis, preventing systematic studies on dopant effects device application.

Here, we report a versatile synthesis method for metal-doped perovskite nanocrystals with precise control over size and doping concentration under ambient conditions. Our room temperature approach results in fully size-tuneable isovalent doping of CsPbX₃ nanocrystals (X = Br, Cl) with various transition metals M²⁺ tested (M = Mn, Ni, Zn). This gives for the first time access to small, yet precisely doped quantum dots beyond the weak confinement regime reported so far. It also enables a comparative study of the photophysics across multiple size and dopant regimes, where we show dopant-induced localisation to dominate over quantum confinement effects. This generalisable, facile synthesis method thus provides a toolbox for engineering perovskite nanocrystals toward light-emitting technologies under industrially relevant conditions. 

Lead halide perovskite nanocrystals (NCs) have emerged recently inspired by the surge of the efficiencies of the solar cells based on thin film perovskites. Two critical problems hindering their widespread application are yet to be resolved: (i) high toxicity due to the presence of heavy metal lead, (ii) relative instability on the presence of various environmental factors. To address these problems, recently, significant efforts to develop lead-free colloidal NCs have been made.[1] Some of the most promising alternative, less toxic, and more stable materials are bismuth halide perovskites (BiHPs), A₃Bi₂X₉. However, there is still a lot of confusion around the synthesis and properties of BiHP NCs for several fundamental and practical reasons: variety of possible structures, potential luminescent impurities, questionable presence of the quantum confinement in such 0D materials, and rare reliable synthetic reports on small BiHP NCs.

In our work, we try to address the above problems using two approaches. First, we have developed rational design to synthesize small and monodisperse colloidal BiHP NCs in a reproducible manner. We study the hot injection synthesis, which allowed obtaining <10 nm-sized NCs by optimizing halide precursors. Then, we will focus on the original method of templated synthesis of BiHP NCs first synthesizing small cesium halide NCs and then converting them by cation insertion into Cs₃Bi₂X₉ NCs with low size dispersion (manuscript in preparation).

In the second part, we will discuss a powerful method for studying the fundamental properties of BiHPs and other Pb-free perovskites by encapsulating them into the mesoporous silica with ordered pores of 2-9 nm.[2] This offers an appropriate means to control the size of the NCs precisely, access small sizes in the quantum confinement regime, and systematically study the effect of size on their properties. The fitted optical absorption spectra revealed that the bandgap of BiHP NCs scale with the pore size. In addition, their exciton binding energies were calculated to be 70-400 meV. It is unambiguously demonstrated for the first time that the 0D BiHPs exhibit the quantum confinement effect. This conclusion is strongly supported by DFT calculations on BiHP clusters with varying dimensions.

Mixed tin-lead (Sn-Pb) perovskite solar cells are promising candidates for next-generation photovoltaics due to their tunable bandgap and potential for high efficiency. Mixed Sn-Pb perovskites possess a close to ideal narrow bandgap for constructing all-perovskite tandem cells to potentially surpass the theoretical efficiency limit of single junction solar cells. One of the main obstacles that need to be overcome is the-oftentimes-low quality of the mixed Sn−Pb perovskite films, largely caused by the facile oxidation of Sn(II) to Sn(IV), as well as the difficulties in controlling film crystallization dynamics. Furthermore, one of the conventional solvent used to process these materials is Dimethyl Sulfoxide (DMSO), which was found to be reduced in the presence of iodide ions, generating in turn iodine-based oxidant species that can degrade Sn(II) perovskite material [1-2]. To address this issue, we investigated the DMSO-free processing of mixed Sn-Pb perovskites.

In our study, we employed methylammonium chloride (MACl) as an additive in a dimethylformamide (DMF)-only solvent system. The introduction of MACl significantly enlarges the grain size, it improves the crystallinity of the perovskite films without introducing new crystalline phases and enhances the optoeelctronic properties of the material. The resulting perovskite solar cells demonstrate efficiencies comparable to control samples processed with traditional DMF/DMSO mixed solvents without additives. More importantly, the devices incorporating MACl exhibit considerably enhanced stability under maximum power point tracking (MPPT), with stable efficiencies for more than 250 hours of continuous operation in N₂ environment. In contrast, control cells reach 80% of the initial power conversion efficiency after only 10 hours, due to a signficant loss in both the open circuit voltage and short circuit current. 

Our findings highlight the potential of DMSO-free processing of mixed Sn-Pb perovskites with MACl additives to overcome the limitations posed by DMSO induced oxidation, paving the way for more stable narrow bandgap perovskite solar cells. This approach provides a promising pathway for the production of high-performance and stable perovskite photovoltaics.