Several photovoltaic technologies have been investigated so far for indoor applications: hydrogenated amorphous silicon, which reached a maximum power conversion efficiency (PCE) of 21% at 1000 lux [1], Dye Sensitized Solar Cells (DSC), which achieved a record of above 30% [2], organic photovoltaics (OPV), that reached a maximum efficiency of above 30% [3], and lead halide perovskites (PSC) that have recently led to an outstanding indoor PCE of 40.1% [4]. 

When moving to flexible substrates, that are very attractive for the low cost manufacturing, the easy integration and the possibility to achieve high power-to-weight ratio [5], the overall efficiency of the devices drops down to about 12% for DSC [6], to about 33% in the case of OPV [7] and to 32.5% for PSC [8].

In this talk, we will focus on and explore the application of flexible perovskite solar cells for indoor light harvesting, spanning from photocapacitors [9] to possible strategies to increase the performance, e.g. tandem configuration with other PV technologies [10], from more sustainable materials (charge transport layers, top electrodes, solvents, etc) [11] to large area deposition techniques with reduced material wastage and energy consumption [12]. 

The escalating demand for sustainable energy solutions in recent years has highlighted the potential of indoor photovoltaics (IPVs) as a viable alternative for powering Internet of Things (IoT) devices. While lead halide perovskites have emerged as frontrunners due to their remarkable power conversion efficiencies (PCE) nearing 45% under indoor lighting conditions, their inclusion of toxic lead has prompted a thorough investigation into safer alternatives. This communication focuses on the sustainability of lead-free perovskite-inspired materials (PIMs), particularly those containing pnictogens such as bismuth (Bi) and antimony (Sb), as promising candidates for IPV applications.[1],[2]

The development of eco-friendly IPV technologies is crucial for reducing reliance on batteries which contribute to environmental degradation through resource extraction and waste generation. Traditional IPV technologies based on amorphous hydrogenated silicon (a-Si:H) offer PCE values up to 30%. However, the innovative use of lead-free PIMs has shown PCEs approaching 10% in early research phases, indicating significant potential for future advancements. This study utilizes a life-cycle assessment (LCA) approach to evaluate the environmental impacts of various PIMs, emphasizing their raw material availability, energy consumption, and waste generation.

Our findings reveal that while the PCE of PIMs plays a pivotal role in their overall environmental footprint and components such as the metal electrode and charge transport layers significantly influence their sustainability. Among the evaluated materials, a Bi-Sb alloy emerged as the most promising candidate, demonstrating a reduced environmental burden compared to a-Si:H under industrial-scale processing conditions. Extended simulations indicate that the industrial-scale implementation of Bi-PIMs can lead to a notable decrease in cumulative energy demand and carbon emissions, showcasing their potential as sustainable IPV technologies.

Moreover, this research underscores the critical importance of exploring the toxicity and criticality of raw materials used in the synthesis of these PIMs. While bismuth is recognized for its negligible toxicity and has been utilized in medical applications, antimony presents concerns regarding its occupational exposure risks.

In conclusion, the sustainability of lead-free PIMs for IPV applications is multi-faceted, encompassing not only their energy conversion efficiencies but also their environmental impacts throughout their lifecycle. Our study provides the first robust evidence of the potential for pnictogen-based PIMs to serve as viable, eco-friendly alternatives to lead-based materials, thereby addressing the growing need for sustainable energy solutions in the rapidly expanding IoT landscape. Future research efforts should focus on optimizing the efficiency of these materials while minimizing their environmental footprints, advancing the development of cost-effective and sustainable IPV technologies. The findings presented herein are crucial for guiding the scientific community and policymakers towards the realization of sustainable energy solutions that are not only efficient but also environmentally responsible.

Two-dimensional layered metal-halide perovskites (2DLPs) are an emerging class of materials, characterized by a semiconducting metal-halide octahedral layer sandwiched between two layers of bulky organic cations. This unique structural arrangement allows for high in-plane mobility of excitons and charge carriers, while the predominantly insulating nature of the organic cations restricts out-of-plane mobility [1], [2]. The latter prevents studies of charge and energy transfer processes in vertical heterostructures. On the other hand, lateral heterostructures, where compositional changes occur along the in-plane direction, offer an interesting platform to explore potential charge transfer mechanisms at the junction interface [3].

To improve the accessibility and quality of heterostructures in 2DLPs, we developed a one-pot synthesis strategy for preparing lateral heterostructures that consist of different halide compositions. Compared to our previous solution-based anion exchange method [4], the presented approach produces consistently heterostructures with high-quality crystalline interfaces between the Br-rich core and the I-rich frame. We systematically investigated the effects of antisolvent, concentration, injection rates, and the Br-to-I ratio. Interestingly, when the iodine content in the precursor solution is increased, the core is eventually consumed, resulting in an I-rich frame-only structure. We attribute this to a combination of partial ion migration on top of the stepwise crystallization process. Additionally, we extended this concept to 2DLPs heterostructures featuring different metal cations including lead-free heterostructure.

The formation of heterojunctions within the in-plane semiconducting layer offers the potential to direct charge carriers or energy flow toward either the edges or the center of these microstructures, which is appealing for applications in energy harvesting and photocatalysis.

Two-dimensional layered lead-halide perovskites (2DLHPs) are currently in the spotlight for their high photoluminescence quantum yield and large structural and functional variety. Their layered structure gives them unique optoelectronic properties such as strong quantum and dielectric confinement^[1]. This makes them highly promising for photonic and optoelectronic applications, and in that respect, achieving precise control over the quality and morphology of the synthesized crystals is crucial for unlocking their full potential.

Here, we developed a solvent-antisolvent recrystallization method to fabricate high-quality 2DLHPs microcrystals (MCs) with flat, nearly step-free surfaces. Our approach involves dissolving pre-synthesized 2DLHPs powder^[2] and fine-tuning of parameters such as solvent/antisolvent choice and ratio, temperature, and saturation conditions. By optimizing these factors, we gained control over their lateral dimensions and thickness, and consistently produced high-quality MCs^[3] on various substrates, including glass, silicon oxide, and gold, as well as on functionalized or pre-patterned areas. The compatibility with diverse substrates broadens the applicability of our MCs, offering seamless integration into devices. Moreover, our protocol demonstrates adaptability to multiple 2DLHP powders, broadening its applicability across different material systems.

The high structural quality and low defect density of the resulting MCs make them particularly suitable for photonic and optoelectronic applications, including light-emitting devices, waveguides, and quantum optics^[4]. Our results represent a significant advancement in the fabrication of 2DLHP MCs, opening promising prospects for future integrations of this material.

Hybrid organic-inorganic perovskites (PVKs) have attracted large interest due to their chemical variability, structural diversity and favourable physical properties [1].

In this work, a new thermochromic composite based on 2D PVKs is presented. Our material is able to switch reversibly from a transparent state (transmittance > 80%) at room temperature to a coloured state (transmittance < 10%) at high temperatures. The process occurs very quickly, requiring only a few seconds for the transition between the bleached and coloured states, and vice versa. Analyses conducted by X-ray diffraction, Fourier-transform infrared spectroscopy, differential scanning calorimetry, rheological and optical measurements during heating and cooling cycles showed that the thermochromic phenomena is based on a reversible disassembly/assembly of PVKs, mediated by polymer chains intercalation. This mechanism occurs through the formation and breaking of hydrogen bonds between the polymer and perovskite [2].

By varying the type and concentration of the organic cations in the formulation, we can regulate the interaction between polymer and perovskite, modulating the switching temperature and kinetics.

This work demonstrates a novel potential of perovskite-based composite, paving the way for their applications in thermoresponsive devices.

A plethora of new semiconductors have recently emerged as versatile materials for solar cells and photocatalytic applications. Combinatorial analytical probes have played a pivotal role in uncovering the mechanisms underpinning light-harvesting performance even before device optimisation has been attempted.

Ultrafast optical probes of photoconductivity dynamics are particularly useful here, uncovering the generation, localisation and ultimate recombination of charge carriers following photon absorption. We report on a peculiar ultrafast self-localisation process observed across wide classes of new bismuth-based semiconductors, including bismuth halides and chalcogenides. We have most recently shown such dynamic transitions from large to small polaronic states to dominate the dynamics of charge carriers in Cs2AgSbxBi1–xBr6 double perovskites,[1] (AgI)x(BiI3)y Rudorffites,[2] and AgBiS2 nanocrystals[3] and discuss the influence of alloying, cation disorder and stoichiometry on such charge-carrier localization events.

Probing charge-carrier motion in highly anisotropic semiconductors poses particular challenges. We show how such charge transport can be probed successfully in layered, two-dimensional (2D) metal halide perovskites that have been found to improve the stability of metal halide perovskite thin films and devices. We show that the 2D perovskites PEA2PbI4 and BA2PbI4 exhibits an excellent in-plane mobilities and exhibit unexpectedly high densities of sustained populations of free charge carriers, surpassing the Saha equation predictions even at low temperature.[4] In addition, we examine the effects of the high anisotropy of transport in thin films comprising layers that are highly oriented either parallel or perpendicular to the substrate plane.[5] We further demonstrate a powerful technique to the degree of transport anisotropy in these materials.

Chiral hybrid organic–inorganic metal halides, including low-dimensional perovskites, showing peculiar nonlinear optical and spin-dependent properties, are triggering a huge interest for their potential use in different applicative areas such as chiroptoelectronics and spintronics. In addition, their intrinsic noncentrosymmetric structure may be exploited in ferroelectric and piezoelectric devices. To date, the number of chiral systems is growing very quickly, and among the different structures reported, 2D chiral perovskites represent the vast majority. However, the structural family of chiral metal halides extends well beyond 2D perovskites and includes several 0D and 1D systems as well as 3D and quasi-2D motifs, which have been prepared using the commercially available chiral amines. As for other metal halide perovskites and low-dimensional systems, a wide range of tuning strategies can be put in place to modulate the (chiro)optical properties also going beyond Pb-based materials. In this presentation, we will show the recent progress of our group in the design of novel chiral metal halides making use of: i) chiral cation modulation (also considering ad-hoc synthesized cations); ii) modulation of B-site metal (i.e., Sn. Ge, Bi, Sb, Cu, Ni, Mn); and iii) halide substitution. The range of structural motifs arising by playing with "chemical degrees of freedom" is huge, providing also novel crystal structures not yet observed in current chiral (and achiral) metal halides. This work on the chemical modulation allows to understand which are the parameters mostly affecting the chiroptical properties of chiral metal halides thus paving the way for a rational design of novel materials [1-3].

Chiral 2D double halide perovskites have become a new trend the past few years due to their lead-free character but also for their promising optoelectronic applications. In this context, we report new 2D double halide perovskite compounds, following the general chemical formula A_{(2 or 4)}Ag^IM^IIIBr₈  where A is either the cystaminium dication (Cyst²⁺, chiral conformation) or the chiral cation (S/R)-1-(4-bromophenyl)ethylammonium (S/R-4BrMBA) and M^III = Sb³⁺, Bi³⁺. Cystaminium is known for its conformational axial chirality change in the solid state,[1] resulting in the synthesis of chiral perovskites and compounds which exhibit phase transition, leading to potential switchable SHG materials.[2]  Driven by this objective, we synthesized and fully characterized the 2D (Cyst)₂AgSbBr₈ compound. DSC measurments showed that this compound exhibits three reversible phase transitions going from Phase 1 (Ph 1) to Phase 2 (Ph 2) (C2/c to C2/m, T = 40°C) upon heating, and upon cooling from Ph 2 to Phase 3 (Ph 3) (C2/m to C2, T = 60°C) and from Ph 3 back to the original compound at T < RT. Therefore, we performed temperature-dependent SHG measurements, highlighting the switchable SHG properties of such compound. The results of the measurement revealed that upon heating the transformation from Ph 1 to Ph 2 occurs via Ph 3 as a SHG signal is observed at 45°C. Upon cooling, the expected SHG signal originated by Ph 3 appears, with the maximum of it being at 11°C. (Figure 1a). The second spacer that we used was the chiral molecule S/R-4BrMBA. The effects of chirality in 2D lead halide perovskites is a newly grown field and based on the lack of chiral 2D double perovskites in the literature, a complete series of 2D bromide-based and iodide-based double perovskites was fully characterized. Thin films were prepared in order to study the chiroptical properties of the materials. The strong modulation of the structure and circular dichroism (CD) properties at the nanoscale is unprecedented, since the thin films of (S/R-4BrMBA)₄AgBiBr₈ strongly evolve from a single-phase compound with small intrinsic CD to a polymorphic material showing a strong increase in the chiroptical signal due to macroscopic effects, something which is not observed for the iodide derivatives (Figure 1b).[3] Such series of compounds will allow us to explore their chirality-induced spin selectivity (CISS) for both the fundamental understanding of the CISS effect and the practical aspect of preparing lead-free spintronic devices.

Over the last decade, metal halide perovskite nanocrystals (LHP NCs) and their derivatives, in the form of nano and bulk crystals, have emerged as a promising class of semiconductor materials with many interesting linear and nonlinear optical properties.¹ The light emission of LHP NCs is not only tunable by their dimensions and composition² but also through self-assembly into ordered architectures.^1-4 Interestingly, LHP NCs spontaneously self-assemble into superlattices and exhibit interesting optical properties such as polarized emission.⁵ On the other hand, low-dimensional metal halide crystals with chiral ligands exhibit chiroptical properties. This talk will be focused on the latest developments in achieving polarized absorption and emission from metal halide crystals either by self-assembly of NCs, using chiral filters, or helical structural engineering.

References

1. Dey et al., State of the Art and Prospects for Halide Perovskite Nanocrystals. ACS Nano 2021, 15 (7), 10775-10981

2. Otero-Martínez et al., Dimensionality Control of Inorganic and Hybrid Perovskite Nanocrystals by Reaction Temperature: From No-Confinement to 3D and 1D Quantum Confinement. Angew. Chem. Int. Ed. 2021, 60 (51), 26677-26684.

3. Vila-Liarte et al., Templated-Assembly of CsPbBr₃ Perovskite Nanocrystals into 2D Photonic Supercrystals with Amplified Spontaneous Emission. Angew. Chem. Int. Ed. 2020, 59 (40), 17750-17756.

4. Gu et al. Color-Tunable Lead Halide Perovskite Single-Mode Chiral Microlasers with Exceptionally High g_lum. Nano Letters 2024. 24, 13333-13340

5. Mendoza‐Carreño et al. Nanoimprinted 2D‐chiral Perovskite Nanocrystal Metasurfaces for Circularly Polarized Photoluminescence. Adv. Mater. 2023, 35, 2210477

Perovskite single crystals have emerged as a promising alternative to polycrystalline samples in optoelectronics and photonics, owing to their exceptional properties such as reduced trap states, enhanced carrier mobilities, and extended diffusion lengths. Despite these advantages, their effective use in devices requires significant effort, particularly in developing specialized growth methods to produce structures with precise dimensions and geometries on a variety of substrates. This talk explores tailored growth strategies, including the capillary bridge and microfluidic-assisted approaches, which enable the synthesis of crystals with predefined shapes, sharp edges, and uniform surfaces.[1,2] By finely tuning growth conditions and controlling interactions within the precursor solution, these methods produce crystals with superior optical properties and performance, making them highly suitable for applications as waveguides and whispering gallery resonators. By achieving such well-defined features, perovskite single crystals demonstrate significant potential to address the specific demands of advanced optoelectronic and photonic devices, paving the way for innovative applications in these fields.

The integration of plasmonic nanoparticles (NPs) into perovskite-based optoelectronic devices offers transformative opportunities to significantly enhance the performance of both perovskite light-emitting diodes (PeLEDs) and perovskite solar cells (PSCs). Perovskite materials, renowned for their exceptional properties—including strong absorption, long carrier diffusion lengths, tunable bandgap, high quantum yield, and narrow emission profiles—are at the forefront of next-generation optoelectronics. However, their full potential remains untapped due to persistent challenges: PeLEDs require further optimization of quantum yield, color purity, and angular light control, amongst others, while PSCs, particularly tandem configurations with narrow-bandgap perovskites, face limitations in absorption capacity that hinder efficiency improvements.

Our research considers meticulous simulation to embed plasmonic NPs randomly distributed into perovskite structures (Figure 1), yielding significant enhancements in their optical properties. By optimizing parameters such as NP composition (Ag, Au, Cu), size, and volumetric concentration, we establish robust design principles to harness plasmonic resonances in optoelectronic devices [1-3].

Rigorous simulations based on the Finite-Difference Time-Domain (FDTD) method demonstrate a three-fold increase in photoluminescence from CsPbBr₃ films embedded with spherical Ag NPs, in comparison to reference films without NPs. This NP design also enables precise control of light directionality, improving device performance across diverse applications. For solar cell applications, our modeling predicts substantial absorption enhancements in perovskite films containing plasmonic NPs. For all-perovskite tandem solar cells, we achieve a 2% absolute improvement in power conversion efficiency for Sn-based perovskites [4]. These gains stem from synergistic near- and far-field plasmonic effects, which also mitigate parasitic absorption and enable the use of thinner perovskite films. Thinner films enhance charge collection and reduce the amount of lead required, addressing both performance and environmental concerns.

We present recent experimental results demonstrating the stable combination of CsPbBr3 nanocrystals and plasmonic NPs in polar solvents [5]. This approach eliminates the need for encapsulation, allowing seamless integration of near- and far-field plasmonic effects, and expanding practical applications.

Nowadays, the existence of high-entropy perovskite oxides is well established, and since their discovery, their fields of application have been continuously studied. The main advantage of these materials, with the general formula ABO₃, lies in the high tunability of their properties through variations in chemical composition. However, the systematic study of their stability, fields of existence, and solubility limits remains underdeveloped compared to the extensive research on their applications, despite the availability of large datasets and computational studies. In our work, we investigated the structure and solubility limits of two families of perovskite oxides using a chemometric approach. We selected lanthanum as the A-site cation due to its stability, while for the B-site, we explored various cation mixtures based on Cr, Mn, Fe, Co, Ni, and Zn. Our goal was to determine the experimental domain by integrating diverse data, including crystal structure, oxygen vacancy content, temperature dependence, and composition. The synthesized samples were analyzed using x-ray diffraction (XRD) followed by Rietveld refinement to extract crystallographic parameters. Neutron diffraction experiments were also performed to obtain precise structural details, especially regarding oxygen positions and non-stoichiometry. Using multivariate analysis, we correlated elemental concentrations with phase stability, crystal symmetry, and cell parameters. This structural study aims to identify potential links between crystal symmetry and the catalytic properties of the materials. Additionally, thermogravimetric analysis was conducted to study non-stoichiometry and phase transitions, which were incorporated into the designated experimental domains. This comprehensive dataset will enable the identification of optimal compositions for desired applications, such as heterogeneous catalysis, solid-oxide fuel cells, and oxygen transport membranes.

The Achilles heel of Sn-based perovskites is their susceptibility to Sn²⁺ to Sn⁴⁺ oxidation. Chemical instability becomes more severe in nanocrystal (NC) form due to the large surface area, while NC durability deteriorates further in the solid state because of higher ligand loss and greater exposure to humidity and oxygen. Recently, an optimized synthetic route was developed, allowing the production of robust and monodisperse three-dimensional (3D) CsSnI₃ nanocrystals (NCs) that coexist with residual amounts of 2D Ruddlesden-Popper nanosheets (NSs) [1].

Herein, the exciton structure and stimulated emission properties of thin films of the tin iodide perovskite nanostructures are discussed. Incorporation of the CsSnI₃ NCs in polystyrene matrixes, increases substantially the optical stability in the oxygen-free environment of the spectroscopic measurements. At ambient temperature, strong NC and weak NS excitonic bands in the red and yellow spectral range, respectively are observed and monitored by transient absorption and photoluminescence (PL). The transient decay of the bleaching of the ground exciton band and the NC luminescence is found to occur at timescales of the order of 0.1 and 1 ns respectively, being accelerated compared to the respective dynamics of lead-based perovskite NC films, most probably due to non-radiative recombination at surface defects. At cryogenic temperatures, two emissive species of the NC structures are observed, identified as bound and free excitonic complexes. The relative population of the two species depends on temperature, aging and surface passivation. Photoexcitation of the CsSnI₃ NCs films with nanosecond pulses activates amplified spontaneous emission (ASE) at temperatures as high as 150 K. The ASE threshold and net modal gain is optimized via the fabrication of NC-polymer multilayer structures, allowing the observation of room temperature ASE.

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Double perovskites and chalcogenide perovskites: variations on the theme.

Lead halide perovskites are photovoltaic absorbers with excellent optoelectronic properties and impressive efficiencies. However, their instability in air and moisture, and the presence of lead (which raises health concerns), pushed the research community for searching for alternatives. Lead-free perovskites have therefore attracted the researchers’ interest, thanks to their varied compositions and diverse properties. In this talk, two different types of lead-free perovskites will be discussed: double perovskites and chalcogenide perovskites. Double perovskites are obtained through heterovalent substitution of Pb²⁺ with a mono and trivalent cation, with a resulting “doubling” of the structure. Cs₂AgBiBr₆, the representative of this family, presents excellent stability in air atmosphere, but low solar cell. On the other hand, chalcogenide perovskites present the traditional perovskite ABX₃ structure but, being X=S^2-, the cations have higher valency (such as Ba²⁺ and Zr⁴⁺ in BaZrS₃). Even if these chalcogenide perovskites have promising optoelectronic features, their synthesis is challenging, resulting in little characterization available and no devices reported.

In this talk, I will present these materials, the reasons behind the discussed limitations and possible strategies to overcome them.

Perovskite solar cells (PSCs) show great promise due to their high efficiency and low manufacturing costs, yet they encounter notable challenges such as optical losses and stability issues, mainly due to high surface reflection and degradation from UV irradiation, and heat[1-3]. In this study, we present a novel, bio-based composite material comprising pectin, polymethyl methacrylate (PMMA), and a spirobifluorene compound designed to mitigate these issues. This innovative composite exhibits high optical transparency, up to 85%, and significant haze (48% at 550 nm), which helps in minimizing reflection-induced losses. The composite incorporates spirobifluorene, which facilitates down-conversion of UV radiation around 350 nm to higher wavelengths above 400 nm, thereby enhancing both photostability and overall device performance. This material, with its lower thermal conductivity compared to glass, also cools the solar cell surface by serving as a thermal barrier. This composite was subsequently attached to the front side of PSCs, which were structured in an inverse architecture (ITO/Me4pacz/SiOx/PSK/C60/SnOx/Cu) for performance measurements and in a different configuration (FTO/c-TiO/m-TiO/PSK/spiro-meotad/gold) for stability tests ( see Figure 1). The composite's implementation leads to up to a 5 ±0.1% increase in the current density and power conversion efficiency of perovskite solar cells. Additionally, it significantly delays initial photodegradation, enhancing T80 life by 1.1-fold for PP-0.25TSBF and 1.9-fold for PP-0.75TSBF. These advancements highlight the potential of this innovative composite to significantly improve the efficiency, stability, and durability of perovskite solar cells, offering a promising route for future photovoltaic technologies.

Heavy-metal chalcohalides are inorganic semiconductors [1], with potential as next-generation optoelectronic materials based on earth-abundant elements. Compared to other semiconductors, usually obtained through colloidal synthesis, chalcohalides combine the simple chemistry of metal halides like CsPbBr₃ with the improved stability of metal chalcogenides like CdS, making them ideal candidates to be explored in the form of nanocrystals. Among them, bismuth-based compounds [2],[3] are particularly promising because of their low toxicity and the high absorption cross-sections, which makes them optimal choices for light harvesting applications. Despite these potential advantages, however, these materials have been explored relatively sparsely so far and primarily in the form of bulk or microcrystals [4].

Herein, a new synthetic route to obtain metallic Bi/Bi₁₃S₁₈Br₂ colloidal nano-heterostructures with dumbbell morphology is presented. This one-pot procedure was developed by modifying the synthesis of Bi-S-X nanocrystals [5] with the controlled introduction of a tertiary amine, which acts as a mild reducing agent. This induces an in-situ nucleation of the metallic bismuth domains on the surface of the semiconductor. By combining electron microscopy and X-ray diffraction we elucidated the  non-trivial growth mechanism of these heterostructures, which proceeds via dual nucleation event (first Bi₁₃S₁₈Br₂ and then metallic-Bi on its surface) followed by a controlled deposition of material at the interface between the two domains.

The combination of a semiconducting and a metallic domain makes our Bi/Bi₁₃S₁₈Br₂ heterostructures interesting materials for photocatalytic applications, as the presence of a heterojunction is expected to enhance the separation of photogenerated carriers and increase their availability for promoting chemical reactions [6]. To assess the photocatalytic activity of these heterostructures, we tested them for the photodegradation of organic dyes like Rhodamine B and Methylene Blue as a proof of concept. Our tests revealed that the Bi/Bi₁₃S₁₈Br₂ heterostructures can efficiently photodegrade the dyes without relevant structural, morphological, and compositional modification for several reuse cycles, demonstrating excellent robustness and stability in polar solvents, like ethanol. The mechanism of photocatalysis will be also discussed. These promising results motivated us to pursue a more in-depth exploration of these and similar heterostructures for photocatalytic applications, which is currently ongoing.

The advent of metal halide perovskite has revolutionised the field of optics and optoelectronics. In particular, the high efficiency of solar cells demonstrated at laboratory scale, now exceeding 26% [1], has stimulated the interest of both researchers and industry in photovoltaic applications.

In this context, the processing of perovskite materials from solution is very attractive, since large amounts of material can be deposited using high-throughput roll-to-roll deposition techniques [2]. Nonetheless, given the strict correlation between the properties of perovskite precursor solutions and the formation of a perovskite film with the desired properties, [3-4] the composition of the ink and the use of additives have been shown to be a crucial aspect in the development of metal halide perovskites with good optoelectronic quality.

In this talk, I will first give an overview of how the incorporation of polymers as additives in precursor inks can afford control over the crystallisation process of metal halide perovskite materials, which is a key aspect for reproducible fabrication of robust films. In particular, I will show how the polymer can influence the stability, mechanical properties and processability of metal halide perovskites that can eventually be printed via roll-to-roll. [5-8]

Finally, I will give an insight into novel functionalities that can be imparted to metal halide perovskites by a judicious selection of polymer matrix, namely the thermochromism and the printability via additive manufacturing techniques for the development of plastic scintillators. [9-10]

The presence of mobile ions in metal halide perovskite materials and charge transport layers have been shown to adversely affect the efficiency, hysteresis and stability of perovskite solar cells (PSCs). Li-TFSI doped Spiro-OMeTAD is the most used hole transport material in n-i-p perovskite solar cells. In the process of device preparation, Li⁺ ions diffuse on the surface of metal electrode, which promotes the oxidation of Spiro-OMeTAD, improves the conductivity of Spiro-OMeTAD. Meanwhile, it is accompanied by the migration of Li⁺ into the cells and enrichment at the perovskite/SnO₂ interface, which promote the extraction efficiency of electrons. [J. Mater. Chem. A. 2021, 9,7575–7585.] However, during the operation of the device, the migration of Li⁺ in SnO₂ will cause hysteresis and "burn-in" degradation. By introducing a thin layer of cross-linked fullerene (CL-PCBM) at the SnO₂/perovskite interface, the "burn-in" degradation can be suppressed. It was revealed that CL-PCBM can fix Li⁺ ions in the SnO₂/perovskite interface, and the introduction of CL-PCBM can increase the built-in potential of the device and improve the electron extraction efficiency. Finally, the power conversion efficiency of 24.19% was achieved, and the "burn-in" degradation process was also eliminated. [Adv. Mater. 2023, 35, 2207656; Adv. Energy Mater.,2023, 2301161]