Colloidal lead halide perovskite (LHP) nanocrystals (NCs), with bright and spectrally narrow photoluminescence (PL) tunable over the entire visible spectral range, are of immense interest as classical and quantum light sources. Attaining pure single-photon emission is key for many quantum technologies, from optical quantum computing to quantum key distribution and quantum imaging.  Across single CsPbX3 NCs (X: Br and I) of different sizes and compositions, we find that increasing quantum confinement is an effective strategy for maximizing single-photon purity due to the suppressed biexciton quantum yield. We achieve 98% single-photon purity (g(2) (0) as low as 2%) from a cavity-free, nonresonantly excited single 6.6 nm CsPbI3 NCs, showcasing the great potential of CsPbX3 NCs as room-temperature highly pure single-photon sources for quantum technologies [1]. In another study, we address the linewidth of the single-photon emission from perovskite NCs at room temperature. By using ab-initio molecular dynamics for simulating exciton-surface-phonon interactions in structurally dynamic CsPbBr3 NCs, followed by single quantum dot optical spectroscopy, we demonstrate that emission line-broadening in these quantum dots is primarily governed by the coupling of excitons to low-energy surface phonons. Mild adjustments of the surface chemical composition allow for attaining much smaller emission linewidths of 35−65 meV (vs. initial values of 70–120 meV), which are on par with the best values known for structurally rigid, colloidal II-VI quantum dots (20−60 meV) [2]. NC self-assembly is a versatile platform for materials engineering, particularly for attaining collective phenomena with perovskite NCs, such as superfluorescence [3, 4, 5]. The NC shape anisotropy leads to structures not observed with spherical NCs. We present a broad structural diversity in multicomponent, long-range ordered superlattices (SLs) comprising highly luminescent cubic CsPbBr3 NCs (and FAPbBr3 NCs) co-assembled with the spherical, truncated cuboid, and disk-shaped NC building blocks. CsPbBr3 nanocubes combined with Fe3O4 or NaGdF4 spheres and truncated cuboid PbS NCs form binary SLs of six structure types with high packing density; namely, AB2, quasi-ternary ABO3, and ABO6 types as well as structures already known in all-spheres systems [NaCl, AlB2, and CuAu types]. In these structures, nanocubes preserve orientational coherence. Combining nanocubes with large and thick NaGdF4 nanodisks results in the orthorhombic SL resembling CaC2 structure with pairs of CsPbBr3 NCs on one lattice site. Also, we implement two substrate-free methods of SL formation. Collective electronic states arise at low temperatures from the dense, periodic packing of NCs, observed as sharp red-shifted bands at 6 K in the photoluminescence and absorption spectra and persisting up to 200 K. Co-assembly of CsPbBr3 nanocubes with very thin disk LaF3 nanodisks (9.2–28.4 nm in diameter, 1.6 nm in thickness) yields six columnar structures with AB, AB2, AB4, and AB6 stoichiometry, not observed before and in our reference experiments with NC systems comprising spheres and disks. Perovskite SLs exhibit superfluorescence, characterized, at high excitation density, by emission pulses with ultrafast (22 ps) radiative decay and Burnham-Chiao ringing behaviour with a strongly accelerated build-up time.

[1] Chenglial Zhu et al. Nano Lett. 2022, 22, 3751−3760

[2] Gabriele Raino et al. Nat. Commun., 2022, 13, 2587

[3] Ihor Cherniukh et al. Nature, 2021, 593, 535–542.

[4] Ihor Cherniukh et al. ACS Nano, 2021, 15, 10, 16488–16500

[5] Ihor Cherniukh et al. ACS Nano, 2022, 16, 5, 7210–7232

We present Pulsed Laser Deposition (PLD) as a physical vapor deposition of halide perovskites, allowing near stoichiometric transfer and multi-element film formation independent of the relative volatility of the elements from a single solid target. We will discuss the effects of deposition pressure, deposition rate and PLD target composition on the formation of stoichiometric and phase-pure films of CsSnI₃, MAPbI₃, MA_1-xFA_xPbI₃ and Cs₂AgBiBr₆. Microstructural, compositional and optoelectronic characterization of the films confirmed that PLD allows control on polymorph formation, optical properties, thickness, and conformal coating on textured substrates [1,2,3]. At the device level, we discuss the influence of the bottom contact layers on the first stages of the perovskite film growth, final film morphology and solar cell performance. Proof-of-concept n-i-p and p-i-n solar cells with > 14 % efficiency are demonstrated with as-deposited room-temperature grown PLD-MA_1-xFA_xPbI₃ films. All these are important steps forward in the controlled growth and future scalability of vapor-deposition methods for perovskite solar cells.[4]

Halide perovskite materials find applications in solar cells, light emitting diodes or memory storage devices. This family of materials are mixed electronic and ionic conductors and the ionic conductivity is responsible for the hysteresis observed in the electrical characterization.¹ Here we explain how this ion migration can be used to our advantage to promote formation of conductive and insulating states making them useful as resistive memories (memristors). We show that the working mechanism and performance of the memory devices can be tuned and improved by a careful selection of each structural layer. Several configurations are  evaluated in which structural layers are modified systematically: formulation of the perovskite², the nature of the buffer layer³  and the nature of the metal contact⁴. In addition, we develop an electrical model to account for the observed j-V response.⁵ Overall, we provide solid understanding on the operational mechanism of halide perovskite memristors that unveils the connection between electronic and ionic conduction.

Besides the outstanding properties such as high absorption coefficient,  bandgap tunability and long diffusion length, organometal halide perovskite devices (MHPs) continue to suffer from the consequences of their dual ionic/electronic nature. Hysteresis behaviour during IV measures is the direct sentinel of the ion migration or defect drift occurring in these devices. But this defect drift or ionic migration in MHPs can be positively utilized to design a novel memory device.  In fact, perovskites are emerging as promising candidates for the next generation of resistive random-access memory (ReRAM) devices or memristors. ReRAM have been developed as promising next-generation of nonvolatile memory devices due to the simple device architecture, fast operation, and low power consumption[1].  Perovskite memristors are being reported lately with remarkable success due to their good electrical performances, meeting the requirements for memory technology; i.e:  non-destructive reading process, nonvolatility, high ON/OFF ratio, and fast switching speed. [2]. Due to their solution processability, perovskite memristor devices have been fabricated both in their polycrystalline and monocrystalline forms, as thin-film and bulk configurations respectively. Outstanding results have been obtained for both.[3] However, the mechanisms behind their good performance and how their crystalline nature affects them are still under discussion. In this work, we report the first memristor device based on MAPbBr₃ thin-film single crystal. The synergy between its thin-film configuration and its monocrystalline nature,  allows displaying very high stability during operation conditions and massive operative currents, exhibiting an outstanding ON/OFF ratio of 10⁶. The mechanisms governing the operation of this device are analysed in depth by impedance spectroscopy measures, contributing to a better understanding of the physics governing these devices.

Radiation detection is of utmost importance in fundamental scientific research, as well as medical diagnostics, homeland security, environmental monitoring and industrial control [1]. Lead halide perovskites (LHPs) are attracting growing attention as high-atomic-number materials for next-generation scintillators and photoconductors for ionizing radiation detection. To unlock their full potential as reliable and cost-effective alternatives to conventional materials [2], it is necessary for LHPs to conjugate high scintillation yields with emission stability under high doses of ionizing radiation. To date, no definitive solution has been devised to optimize the scintillation efficiency and kinetics of LHPs and nothing is known of their radiation hardness for doses above a few kiloGrays, to the best of our knowledge. Here we demonstrate that CsPbBr3 nanocrystals exhibit exceptional radiation hardness for γ-radiation doses as high as 1 MGy [3]. Spectroscopic and radiometric experiments highlight that despite their defect tolerance, standard CsPbBr3 nanocrystals suffer from electron trapping in dense surface effects that are eliminated by post-synthesis fluorination. This results in >500% enhancement in scintillation efficiency, which becomes comparable to commercial scintillators, and still retaining exceptional levels of radiation hardness. These results have important implications for the widespread use of LHPs in ultrastable and efficient radiation detectors for strategic applications such as national and industrial security, high-energy physics and nuclear power plant control, from space exploration to medical imaging diagnostics such as CT and PET.

The detection of ionising radiation is the focus of many strategic applications in both science and technology. Typically, the detection is carried out by scintillator materials that emit light following interaction with ionising radiation, which is detected by highly sensitive photodetectors. The fundamental characteristics of scintillators are the probability of interaction with ionising radiation, scintillation yield, scintillation rate, and stability to high doses of absorbed radiation, commonly referred to radiation hardness. For large scale applications, it is essential that scintillators can be manufactured in large sizes and massive quantities with cost-effective techniques in terms of both energy and raw material consumption.

Recently, lead halide perovskite nanocrystals (LHP-NCs)^[1] have emerged as promising nanoscintillators prized for their tuneable optical properties, radiation stability, high average Z-number and defect tolerance that enables high light yields and resistance to radiation damage up to extreme radiation levels^[2]. However, hot-injection synthesis methods used for high-optical-quality LHP NCs are not suitable for mass production and scalable LARP approaches are limited by concentration gradients in the reaction environment resulting in poorer optical performance. LHP-NCs are also susceptible to the fabrication protocols for polymeric matrices mostly due to the polarity of monomers, the presence of initiators and the polymerization temperature that lead to surface damage, NC dissolution and/or phase shift to non-emissive allotropes.

In this talk, I will report the fabrication of new ultrafast and radiation hard plastic scintillators based on CsPbBr₃ NCs formed within a polyacrylate matrix from precursor nanoparticles synthesized by a high-throughput, large scale turbo-emulsion method. Importantly, the formation of CsPbBr₃ NCs is accompanied by the gradual curing of quenching defects, resulting in large size nanocomposites with photoluminescence quantum yield of ~90% and light yield of about 1000 ph/MeV for NC loading of only 0.2wt%. Radiometry experiments after as much as 1 MGy of certified γ-ray dose from ⁶⁰Co source reveal perfect radiation hardness. Also fundamentally, pulsed X-ray scintillation measurements demonstrate ultrafast <60 ps scintillation due to multi-excitonic radiative decay as further confirmed by transient absorption measurements, indicating that CsPbBr₃ NCs are efficient scintillators despite the negative effects of nonradiative Auger decay.

The combination of fabrication scalability with ultrafast and stable scintillation under extreme operational conditions represents offers a valid platform for future advancements in radiation detection schemes, in particular for time-of-flight radiometry applications in high-energy physics and medical diagnostics.

In the last decades, the interest in nanoparticles in the biomedical field experienced a rapid growth because of the tunability of their physical and chemical properties and their rich surface chemistry that enables specific functionalization by design. Different classes of functional nanoparticles, including metals, semiconductors, metal/lanthanide oxides and organic or hybrid systems have found successful application in several medical branches, such as nano-therapy, diagnostics and imaging. Today, one of the most advanced biomedical uses of nanoparticles is offered by their strong interaction with ionizing radiation, which makes it possible to improve the effectiveness of conventional cancer treatments, imaging techniques and radiation dosimetry [1]. In oncological therapies, one of the most adopted medical treatment is radiotherapy (ca. 50% of total cases), a non-invasive technique typically consisting in the local release of the energy of X-rays to stop tumor cells proliferation, either by directly damaging their DNA, or indirectly by forming cytotoxic free radicals [2]. Among the different material classes with potential application in this field, metal halide nanocrystals (NCs) have recently attracted substantial attention for ionizing radiation detection, prized for their high average atomic number (Z) that enhances the interaction probability with ionizing radiation and strong robustness to prolonged exposure to ionizing radiation [3][4][5]. However, despite such promise, very few examples of medical diagnostic and therapeutic strategies based on metal halide NCs have been proposed mainly due to their low stability in aqueous environment resulting in their rapid dissolution and further consequent release of potentially harmful Pb²⁺ ions.

In this talk, we show that multicomponent systems consisting of lead halide perovskite NCs (CsPbX₃-NCs, X=Br, I) grown inside mesoporous silica nanospheres (NSs) with selectively sealed pores are potentially promising candidates for enhanced radiotherapy and radio-imaging strategies, yhanks to the intense scintillation and strong interaction with ionizing radiation of CsPbX₃ NCs with the chemical robustness in aqueous environment of silica particles. We demonstrate that CsPbX₃ NCs boost the generation of singlet oxygen species (¹O₂) in water under X-ray irradiation and the encapsulation into sealed SiO₂ NSs warrants perfect preservation of the inner NCs after prolonged storage in harsh conditions. We find that the ¹O₂ production is triggered by the electromagnetic shower released by the CsPbX₃ NCs with a striking correlation with the halide composition (I₃>I_3-xBr_x>Br₃), without quenching their radioluminescence. This opens to the possibility of designing multifunctional radio-sensitizers able to reduce the local delivered dose and the undesired collateral effects in the surrounding healthy tissues by improving a localized cytotoxic effect of therapeutic treatments and concomitantly enabling optical diagnostics by radio imaging.

One of the main thrusts of medical X-ray imaging is to minimize the X-ray dose acquired by the patient, down to the fundamental limit set by the Poisson photon statistics. Such low-dose X-ray detection characteristics have been demonstrated with only a few direct-detection semiconductor materials such as Si and CdTe; however, their industrial deployment in medical diagnostics is still impeded by elaborate and costly fabrication processes. Hybrid metal halide perovskites – newcomer semiconductors -– make for a viable alternative owing to their scalable, inexpensive, robust, and versatile solution growth and recent demonstrations of single gamma-photon counting under high applied bias voltages. The major hurdle with perovskites as mixed electronic-ionic conductors, however, arises from the rapid material's degradation under high electric field, thus far used in perovskite X-ray detectors. Here we discuss the negative effects of the ion migration on X-ray detection performance and demonstrate the mitigation path by utilizing the perovskite X-ray detectors in the photovoltaic mode of operation at zero-voltage bias. We show both countings of almost every single incoming photon and long-term stable performance, by employing thick and uniform methylammonium lead iodide single crystal films, solution-grown directly on hole-transporting electrodes The operational device stability is equivalent to the intrinsic chemical shelf lifetime of MAPbI₃, being at least one year in the studied case. Furthermore, direct readout array integration of detectors is demonstrated as well. A high spatial resolution of 11 lp mm^-1 is obtained with a linear detector array. We also comment the lack of a clear commonly accepted X-ray detection characterization, approach, particularly in material research community, often leads to a misguiding assessment of performance.  We propose the guidelines for the determination of figures of merit for the low-dose X-ray imagers. These findings pave the path for the implementation of hybrid perovskites in low-cost and low-dose commercial detector arrays for X-ray imaging.

Metal halide perovskites have now achieved impressive power conversion efficiencies (PCEs) in both single junction and tandem solar cells, making them promising candidates to solve energy and environment crisis. Record efficiencies of perovskite solar cells (PSCs) are obtained with doped spiro-OMeTAD as the hole transport layer (HTL). Conventionally, spiro-OMeTAD is doped by hygroscopic lithium salts with the assistance of volatile 4-tert-butylpyridine, which, however, brings a time-consuming doping process as well as poor device stability. To exclude the aforementioned disadvantages, researchers have tried to replace the LiTFSI with other dopants, like other metallic salts, F4TCNQ or organic radicals, which could also help to generate radicals improving the conductivity and get rid of the moisture sensitive byproduct LixOy. However, all the recipes with varied dopants can only achieve high PCE with tBP, but the mechanism behind have not been fully discussed to the point. Here, we develop an instantly effective (without post oxidation) doping strategy for spiro-OMeTAD, by employing stable organic radicals and ionic salts (referred to as ion-modulated (IM) radical doping). We achieve high power conversion efficiencies (PCEs) over 25% and much improved device stability under harsh conditions. In addition, the IM doping mechanism was revealed through advanced characterizations and theoretical analysis: electron transfer from neutral spiro-OMeTAD to radicals provide free holes to instantly increase the conductivity and work function (WF); the electrostatic interactions from ionic salts further modulate the WF by affecting the electron transfer activation energy. Our IM radical doping strategy proves effective with a variety of ionic salts, and the doped spiro-OMeTAD demonstrates universal applicability in different PSCs. The understandings on the doping mechanism also solve the mystery of tBP in conventional spiro-OMeTAD doping. Last but not least, the IM doping strategy addressed the importance of localized electrostatic environment in organic doping process, offering new insights for organic semiconductor doping by decoupling the conductivity and WF tunability, and can find applications in a number of optoelectronic devices.

Since the emergence of hybrid perovskite photovoltaics in 2009 the scientific community has witnessed disruptive progress of the technology in terms of solar to electric power conversion efficiency (25.7%) [1] accompanied by advancement in addressing stability issues and developing a deeper understanding of fundamental structure-processing-property relationships. Merely a decade after discovery, the commercialization of organic-inorganic metal halide perovskites photovoltaic devices is just around the corner! Many issues had to be tackled to meet industrialization, among them large area deposition techniques, safety standards and material wastage without compromising efficiency and stability. Saule technologies has been developing a fully scalable inkjet printing process of perovskite solar cell modules on lightweight flexible substrates. This talk will focus on recent advancements in the technology and the product development process required to bring inkjet printed perovskite modules closer to market entry. Moreover, it will underline the unique properties of the inkjet printing technique, which allow scalable solution-based fabrication of high-quality perovskite films and devices, processed in ambient atmosphere. [1] https://www.nrel.gov/pv/cell-efficiency.html

Recent experiments involving a new carbon electrode demonstrate a true fully roll to roll coated perovskite solar cell via a continous slot die coating method. All previous reports of roll to roll coated perovskite solar cells have completed the device off-line with an evaporated metal contact. The application of a wet carbon film continuously and compatibly with an underlying perovskite device stack in a moving web at manufacturing speeds is complex but game-changing. The ability to sequentially deposit all layers of the device stack culminating in a fully working device entirely in-line means that the promise of high volume “liquid in/solar cell out” can be realised.

This multifunctional carbon electrode can be safely deposited on top of a layered solar cell without any deformation or dissolution of the underlying layers. The new contact material overcomes issues of solvent incompatibility, interface incompatibility and narrow rheology and heating process windows.

In this talk we will present the development journey of this new electrode material and the recent succesful pilot run of the material. In particular we will show how we formulate a new carbon ink with solvent compatible with the perovskite stack that crucially has suitable boiling point for low temperature, high speed processing coupled with very low toxicity (no work place exposure limit). The solid loading of the ink is optimised for a rheological profile suitable for slot die and we demonstrate the roll to roll slot die coating of the electrode sequentially following the roll to roll coating of the NIP device stack incorporating a low temperature processed p type interlayer. The carbon ink is formulated with solvent system orthogonal with the device stack and with no detrimental action on the perovskite active layer as shown through X-ray diffraction analysis. Electrochemical impedance spectroscopy and steady state photoluminescence analysis reveal that charge transfer at the interface is equivalent to evaporated gold electrodes. Further, the device stack is demonstrated to have no detrimental effect on stability, unencapsulated cells retained 90% of original PCE at atmospheric temperature for 1000 hours and outperform gold electrode cells at elevated temperature.

This work introduces the very first entirely roll to roll devices achieving efficiency matching evaporated gold electrodes. This first fully roll-to-roll coated perovskite prototype promises the possibility of transferring to industrially efficient PV production in the near future.

Since 2014, Oxford PV has been focused on the integration of perovskite PV in tandem configuration with silicon, holding the world record in large area at 26.8%. Less than a decade later, perovskite-on-silicon modules are close to enter the market. This achievement is the result of an accelerated effort to address efficiencies, technology fundamentals, manufacturing processes and supply chain, all under a sustainable perspective.

Energy security concerns have accelerated the deployment of solar, this opportunity for a faster transition to clean energies, comes with the added responsibility to making sure it considers the needs of generations to come. In this presentation, I will show Oxford PV’s sustainable journey, where environmental considerations go in parallel with the selection of materials, product designs and manufacturing processes, together with operational factors. Perovskite PV market integration comes with many challenges, but also the great opportunity to be the most efficient and sustainable solar energy source

Abstract:

Wide bandgap perovskite materials show promising potential as tandem top cells to pair with silicon bottom cells and achieve power conversion efficiencies (PCEs) over 32%, while the fabrication costs are likely to stay low. To date, most of the efficient wide bandgap perovskite layers are fabricated by spin coating, which is difficult to scale up to large area and the crystallization mechanism remains unknown. In this work, we report on slot-die coating for an efficient, wide bandgap triple-halide perovskite, (Cs_0.22FA_0.78)Pb(I_0.85Br_0.15)₃ + 5 mol% MAPbCl₃^{1 2}. A suitable solvent system was designed and optimized specifically for the slot-die coating technique. We demonstrate that with this perovskite, our fabrication route enables a bandgap of 1.68 eV which is suitable for tandem solar cells, and without phase segregation typically observed for high Br loadings. The slot-die coated wet perovskite film was dried using a stream of nitrogen (N₂) from an ''N₂ knife'' with high reproducibility, and avoiding the need to use antisolvents.

We explored varying drying and annealing conditions from 100°C to 170°C and measured absolute as well as transient photoluminescence (PL) to extract information about the perovskite bandgap, quasi Fermi level splitting (QFLS) and charge carrier lifetimes. We find parameters allowing to crystallize the perovskite film into large grains reducing charge collection losses and thus enabling higher current density in solar cells (Fig. 1B). With annealing at 150 °C, an optimized tradeoff between crystallization and the detrimental formation of PbI₂ aggregates on the film’s top surface is found. Insitu Grazing-Incidence Wide-Angle X-ray Scattering (GIWAXS) investigation of the solution intermediate and film annealing at various stages has also unveiled the perovskite crystallization and PbI₂ formation processes. With the optimized annealing conditions, we improve the cell stability and performance of perovskite single junction cells towards a stabilized power output of up to 19.4 %.

By integrating the optimized perovskite fabrication with commercial saw damage etched Czochralski silicon bottom cells, a two-terminal monolithic tandem solar cell with a PCE of 25.2 % on 1 cm² active area is demonstrated with fully scalable processes. Note that this is reached for a wafer thickness of around 120 µm, not enabling the full photocurrent potential in the NIR wavelength regime compared to thicker wafers (> 250 µm) that are typically used in literature. Furthermore, a 4 cm² tandem solar cell has been developed with this fabrication route and using screen printed silver front grids, yielding PCEs up to 24 %. 

Finally, we show a detailed comparison between spin coated and slot-die coated perovskite films. For the solar cells, we present the loss mechanisms as well as guidelines for further improving the printed films. With that, we highlight the high potential for slot-die coating as fabrication route for scalable and industrially relevant perovskite/silicon tandem solar cells.

While light-emitting diodes (LEDs) made from lead halide perovskites have demonstrated external quantum efficiencies (EQEs) well over 20% [1]–[4], their electrical stability must be addressed before they are seriously considered for commercial applications [5]–[8]. In an effort to improve the optoelectronic properties of lead halide perovskites for light emission, many researchers have investigated introducing both alkaline-earth metal ions [9], [10] (e.g., Ba²⁺ and Sr²⁺) and transition metal ions [11]–[13] (e.g., Mn²⁺, Zn²⁺, Cd²⁺, and Ni²⁺) into the B-site of the perovskite’s ABX₃ structure. Additionally, the factors that limit the electrical stability of perovskite LEDs remain under investigation [5]–[7], [14]–[16]. In this work, we dope Mn²⁺ ions into an organic-inorganic hybrid quasi-bulk 3D perovskite resulting into (PEABr)_0.2Cs_0.4MA_0.6Pb_0.7Mn_0.3Br₃ thin films with the addition of tris(4-fluorophenyl)phosphine oxide (TFPPO) dissolved in a chloroform antisolvent to achieve an EQE of 13.4% and a peak luminance of 95,400 cd/m². While the inclusion of TFPPO into the chloroform antisolvent dramatically increases the EQE of perovskite LEDs, the electrical stability is severely compromised. At an electrical bias of 5 mA/cm², our perovskite LED fabricated with a pure chloroform antisolvent (2.5% EQE) decays to half of its initial luminance in 90.68 minutes. Alternatively, our perovskite LED fabricated with TFPPO (13.4% EQE) decays to half of its initial luminance in 2.07 min. In order to investigate this trade-off in EQE and electrical stability, we study both photophysical and electronic characteristics before and after electrical degradation of the perovskite LEDs. We find that given identical electrical degradation conditions, the TFPPO-based device’s turn on voltage and overall electrical resistance increases in a much larger fashion as compared to the pure chloroform-based device. While the EQE characteristics of this Mn²⁺-doped perovskite LED show promise for B-site engineered perovskites, there is still large concern to simultaneously achieve both energy-efficient and electrically stable perovskite-enabled lighting. Uncovering the effects from the TFPPO additive on perovskite LEDs will reveal pathways on how to mitigate their negative consequences on electrical stability while retaining their energy-efficiency boosting properties.

After establishing themselves as promising active materials in the field of solar cells, perovskites are currently being explored for fabrication of low-cost, easy processable and highly efficient light emitting diodes (LEDs). Even though higher efficiencies are reported for perovskite-based LEDs (PeLEDs), the fabrication technique used is spin coated or vacuum evaporation. Herein, we show a successful incorporation of air stable inkjet-printed (IJP) NiOX as an electron blocking layer (EBL) in addition to poly(3,4‑ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) as hole injection layer. 2,4,6-tris[3(diphenylphosphinyl)phenyl]-1,3,5-triazine (POT2T) or inkjet-printed (IJP) SnO2 as hole blocking layer (HBL). Individual layer properties and the morphology of IJP NiOX were analysed through X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-Vis spectroscopy. Comparing p-n junction diodes with and without IJP NiOX as EBL shows a low leakage current and good rectification behaviour. Owing to its higher valence band levels, high hole mobility, low trap density at its interface with perovskite, PeLEDs with IJP NiOX and POT2T achieved higher luminance values of 19230 cd m-2 and an EQE of ~ 2.5 % using IJP of high purity CsPbBr3 layers. Furthermore, all inkjet printed PeLEDs replacing IJP SnO2 reached a luminance of 324 cd/m2 with an EQE of 0.017 %. Thus, an ambient processed PeLED with inorganic perovskite sandwiched between inorganic charge injection layers (CILs) which are also inkjet-printed is demonstrated. The results potentially lay a route towards ambient processed air stable all inorganic fully inkjet-printed PeLEDs.

Engineering the chemical composition of metal-halide perovskites via halide mixing allows a facile bandgap modulation but renders perovskite materials prone to photoinduced halide segregation.[1] Triple-halide alloys containing Cl, I,
and Br were recently reported as a means to stabilize Cs_yFA_1–yPb(Br_xI_1–x)₃ perovskite under illumination.[2] Herein, these triple-halide alloys are found to be intrinsically less stable with respect to the reference I-Br in ambient conditions. By exploiting the influence of low-molecular-weight organic gelators on the crystallization of the perovskite material, a triple-halide alloy with improved moisture tolerance and thermal stability at temperatures as high as 120 °C is demonstrated.
The hydroxyl-terminated organic gelators are found to aggregate into nanoscale fibers and promote the gelation of the solvent inducing the formation of a 3D network, positively interfering with perovskite solidification. The addition
of a tiny amount of organic gelators imparts a more compact morphology, higher crystallinity, and compositional stability to the resulting triple-halide polycrystalline films, making them more robust over time without compromising the
photovoltaic performance.[3] Overall, this approach offers a solution toward fabrication of active perovskite materials with higher energy gap and improved stability, making these triple-halide alloys truly exploitable in solar cells.

Inorganic cesium lead iodide (CsPbI₃) perovskite solar cells (PSCs) have attracted enormous attention due to their promising thermal stability and optical bandgap (~1.73 eV), making them particularly well-suited for tandem device applications. Although the performance of CsPbI₃ PSCs has surged to over 20%, most high-performance devices are fabricated using the dimethylammoniumiodide (DMAI)-assisted method, which hinders the options for mass production. Furthermore, the potential presence of the organic component DMA in the final CsPbI₃ films remains under debate. Therefore, it is imperative to develop a plethora of methods to fabricate highly phase-pure CsPbI₃ thin films. However, many methods of fabricating such CsPbI₃ films require processing at high-temperatures (~340 ℃), which limits their applicability on flexible substrates. Thus, it is still challenging to achieve high-performing photovoltaic devices processed at low temperatures.

Here we reported a new method to fabricate high-efficiency and stable γ-CsPbI₃ PSCs at low temperatures (~180 ℃) by introducing long-chain organic cation salt ethane-1,2-diammonium iodide (EDAI₂) and regulating the content of lead acetate (Pb(OAc)₂) in the perovskite precursor solution. By optimizing the excess amount of Pb(OAc)₂ in the precursor solution, we demonstrate improved crystallinity, morphology and reduced carrier recombination are observed in the EDAI₂ and Pb(OAc)₂ synergistically stabilized CsPbI₃ films. By optimizing the hole transport layer of CsPbI₃ inverted architecture solar cells, we demonstrate efficiencies of up to 16.6%, which surpass previous reports examining γ-CsPbI₃ in inverted PSCs. Notably, the encapsulated solar cells maintain 97% of their initial efficiency at room temperature and dim light for 25 days, demonstrating the synergistic effect of EDAI₂ and Pb(OAc)₂ in stabilizing γ-CsPbI₃ PSCs.

Metal halide perovskite photovoltaics (MHP) faces fundamental challenges which hinder their tangible impact on the final applications, with performance and stability being critical limiting parameters. Adjusting the perovskite grain boundaries and the crystalline surface are the primary tools to overcome these issues. Additionally, the research in new selective transport materials also plays a key role in improving optoelectrical devices' stability and performance to their theoretical limit to extend the perovskite application range.

Beyond efficiency and stability issues, perovskite photovoltaics must rely on sustainable technology for a feasible and fast green transition. Sustainability simultaneously considers environmental, economic, and social dimensions. Any sustainable technology must: a) generate enough power with reduced space usage (efficiency), b) be cost-effective, and c) not be detrimental to the environment or society. The environmental impact of the device fabrication is seriously affected not only by harmful materials (heavy metals and solvents) but also by the energy consumption of the synthetic and deposition routes used at the laboratory scale, which are not realistic for scaled-up manufacturing. Therefore, developing low-demanding synthetic routes is compulsory for a fast green transition.

Here, we present the research already performed by our team towards the synthesis and passivation methods of device-oriented metal halide perovskites (monocrystals at the macro and nanoscale) and metal oxides as selective transport materials. Our synthetic routes are mainly based on the in-situ synthesis approach. This one-step, low-cost, and low-demanding approach offers the possibility of modifying the precursor solution formulation very easily to adapt them to commercial-available printing techniques, one of the reasons behind MHP's success. Regarding sustainability, the in-situ synthesis approach is a low-carbon footprint synthetic route compared to traditional wet chemistry and colloidal routes. Following the global tendency to develop solution-processed materials, we have been involved for years in the in-situ synthesis approach of different materials, from MHP [1,2] to metal oxides [3] and conducting polymers [4]. We will show our work with solution-processed MHP and transparent metal oxides formulated as precursor inks compatible with roll-to-roll printing for large-scale production. The working principle analysis, including electrical and optical techniques, displays how the optoelectrical response can be adjusted by controlling the crystal growth and synthesis conditions and surface passivation, which can be linked to fundamental variations in the surface and bulk structure and composition.

_{1. Low-demanding in situ crystallization method for tunable and stable perovskite nanoparticle thin films}

_{J. Noguera-Gómez, I. Fernández-Guillen, P. F. Betancur, V. S. Chirvony, P. P. Boix, R. Abargues.}

_{Matter. 2022, 5, 3541-3552}

_{https://doi.org/10.1016/j.matt.2022.07.017}

_{2. Spray-driven halide exchange in solid-state CsPbX3 nanocrystal films}

_{RI Sánchez-Alarcón, J Noguera-Gomez, VS Chirvony, H Pashaei Adl, Pablo P Boix, G Alarcón-Flores, JP Martínez-Pastor, R Abargues.}

_{Nanoscale. 2022, 14 (36), 13214-13226}

_{https://doi.org/10.1039/D2NR03262G}

_{3. Solution-processed Ni-based nanocomposite electrocatalysts: an approach to highly efficient electrochemical water splitting.}

_{J. Noguera-Gómez, M. García-Tecedor, J. F. Sánchez-Royo, L. M. Valencia Liñán, M. Herrera-Collado, S. I. Molina, R. Abargues, and S. Giménez.}

_{ACS Appl. Energy Mater. 2021, 4, 5255-5264}

_{https://doi.org/10.1021/acsaem.1c00776}

_{4. In Situ Synthesis of Polythiophene and Silver Nanoparticles within a PMMA Matrix: A Nanocomposite Approach to Thermoelectrics}

_{J F Serrano-Claumarchirant, A Seijas-Da Silva, J F Sanchez-Royo, M Culebras, A Cantarero, C M Gómez, R Abargues}

_{ACS Applied Energy Materials 2022, 5 (9), 11067-11076}

The mixture of inorganic quantum dots and hybrid perovskite in one nanocomposite is considered a favorable approach to overcome restrictions of metastable perovskite. However, to date only few examples of improved opto-electronic perovskites have been realized with such materials. Here, we show a systematic approach to characterize the standard methylammonium lead iodide (MAPbI3) perovskite system by: (i) the substitution of some MA by guanidinium (Gu); (ii) the incorporation of PbS quantum dot (QD) additives and (iii) addition of both Gu and PbS at the same time. We studied the effect of the incorporations of the big cation on the film strain and crystal cell unit volume, and on the solar cell device efficiency and stability. With the control of Gu and PbS QD content, higher performance and longer solar cell stability are obtained. PbS QDs aid Gu incorporation, resulting in an expected more stable material and devices with high amount of guanidnium. From the optical point view, the tuning of the energy levels of perovskite nanocomposite with PbS with different ligands will be also exemplified, to show that a slight shift of the energy level leads to improved efficiencies especially in the case of formamidinium/PbI₂ capping ligand. With this study, we demonstrated the reason why the solar cells performances are improved up to 20%, even when the optical properties are detrimental.

Since the seminal report on the 9.7% efficient and 500 h-stable solid-state perovskite solar cell (PSC) in 2012 based on methylammonium lead iodide, power conversion efficiency (PCE) was swiftly increased to 25.7% due to unique photophysical property of halide perovskite. According to Web of Science, number of publications on PSCs increases exponentially since 2012, leading to the accumulated publications of more than 30,900 as of December 2022. PSC is regarded as a game changer in photovoltaics because of low-cost and high efficiency surpassing the conventional high efficiency thin film technologies. High photovoltaic performance was realized by compositional engineering, device architecture and fabrication methodologies for a decade. Toward theoretical efficiency over 30% along with long-term stability, exquisite control of light management and photo-excited charges are highly required, along with thermodynamic phase stability. In this talk, facet engineering of perovskite films is reported. A specific crystal facet was found to have strong interaction with photon, leading to high photocurrent. Furthermore, a certain facet was found to be quite stable under moisture and PSC based on a perovskite film with abundant moisture-tolerant facet was remarkably stable in humid atmosphere even without encapsulation.

Halide perovskites constitute a fascinating family of materials that has revolutionized the optoelectronic field in the last decade. Halide perovskite are soft materials presenting a benign defect physics that can be prepared a relative low temperature. This appealing property, from the point of view of industrialization, also makes of material and device stability the Achiles heel of the optoelectronic halide perovskite technology. Consequently, the development of stabilization procedures is probably the current main topic of these systems. The soft nature that limits stability also allows the easy combination of halide perovskites with other materials. In this talk we show as an accurate choice of additives can promote interesting synergies boosting the long term stability of halide perovskites devices. We show how the use of PbS quantum dots increases significantly the stability of FAPbI3. Incorporation of PbS QDs allows the dramatic decrease of the annealing temperature for the formation of black FAPbI3 phase perovskite thin film, from the 170ºC required without QDs to 85ºC when QDs are present. We have also verified the synergic combination of different additives for a significant increase of device stability of Pb free Sn-based solar cells, LEDs and lasers. Eventually, stabilization of halide perovskite nanoparticles is a necessary step for the development of high performance Halide Perovskite LEDs. Control of post synthetic washing processes as well as nanoparticle capping allows the preparation of LEDs with enhanced performance and stability.

Mixed Tin/Lead (Sn/Pb) perovskites have the potential to achieve higher performances in single junction solar cells than Pb-based compounds. The best Sn/Pb based devices are fabricated in the p-i-n structure and frequently PEDOT: PSS is utilized as hole transport layer, even if there are many doubts on a possible detrimental role of this conductive polymer. Here, we propose the use of [2-(9H-Carbazol-9-yl)ethyl]phosphonic acid (2PACz) and the functionalized [2-(3, 6-dibromo-9H-carbazol-9-yl) ethyl] phosphonic acid (Br-2PACz) version, as substitutes for PEDOT: PSS. By using Br-2PACz as HTL we achieve record efficiency (19.51%) with the perovskite composition Cs_0.25FA_0.75Sn_0.5Pb_0.5I₃ without any anti-reflective coating. The halogen functionalization of the SAMs is an efficient way to improve both the device performances and stability. Several factors seem to determine these improvements. The two carbazole-based molecules are able to form a self-assembled monolayer which show minimal parasitic absorption and low charge recombination when compared to PEDOT: PSS films. Additionally, the perovskite layer deposited on SAMs show an higher crystallinity, with reduced pinhole density and larger grains. The defect density for the perovskite films was also reduced when deposited on Br-2PACz or 2PACz compared to PEDOT: PSS. PL and TRPL measurements further confirmed the better perovskite film quality when deposited on SAMs, with reduced charge recombination.

Finally, the wettability of the perovskite precursor solution on top of the SAMs is a problem which limits SAMs application in Sn- or mixed Sn/Pb- perovskite solar cells on a large scale, limiting enormously the yield of device fabrication. I will present a solution for this issue, that may allow to improve both the scalability and reproducibility of the SAMs-based perovskite solar cell.

Metal-Halide Perovskite (MHP) photovoltaic (PV) modules are at the cusp of commercialization. One major hurdle that remains is establishing confidence in long-term field performance and durability of MHP modules. A lot of progress has been made in addressing many performance stability issues in MHP cells and modules; however, there is still work to be done to understand degradation and demonstrate real world operation of this technology. In this talk I will share examples of both lab-scale and field studies to improve our understanding of MHP solar cell and module degradation mechanisms. First, I will discuss an application of X-ray scattering methods to probe the nanoscale heterogeneity of metal halide perovskite absorber layers and couple these results to device level stability studies to understand the role heterogeneity plays in device performance. I will then present a brief overview of an initial field demonstration of MHP modules as part of the Perovskite PV Accelerator for Commercializing Technologies (PACT) program. Together this work aims to improve our confidence in real world MHP module performance.

In this work I will present two new concepts related to hybrid perovskite synthesis and devices.

(i) Chiral molecules were implemented into hybrid perovskite forming 2D hybrid perovskite with chirality properties. We used the two enantiomers R)-(+)-α-Methylbenzylamine (R-MBA) and, (S)-(-)-α-Methylbenzylamine (S-MBA). The chirality is manifested at low n values and pure 2D structure measured by circular dichroism (CD). The anisotropy factor (gabs) decreased by an order of magnitude when decreasing the n value achieving 0.0062 for pure 2D. Ab initio many-body perturbation theory successfully describes the band gaps, absorbance and CD measurements. For the first time these quasi 2D chiral perovskites were integrated into the solar cell. Using circular polarization (CP) and cut off filter we were able to distinguish the chirality effect from the solar cells photovoltaic response.

(ii) In the second part we developed unique fully printable mesoporous indium tin oxide (ITO) perovskite solar cell. In this structure, the perovskite is not forming a separate layer but fills the pores of the triple-oxide structure. One of the advantageous of this solar cell structure is the transparent contact (mesoporous ITO) which permit the use of this cell structure in bifacial configuration without the need for additional layers or thinner counter electrode. We performed full characterizations on both sides (i.e. ITO-side and glass-side) and elucidate the solar cell mechanism, where the glass side show 15.3% efficiency compare to 3.8% of the ITO-side. Further study of the mechanism shows that the dominant mechanism when illuminating from the glass-side is Shockley-Read-Hall recombination in the bulk, while illuminating from the ITO-side show recombination in multiple traps and inter gap defect distribution which explain the poor PV performance of the ITO-side. Electrochemical impedance spectroscopy shed more light on the resistance and capacitance. Finally, we demonstrate 18.3% efficiency in bifacial configuration. This work shows a fully printable solar cell structure which can function in bifacial configuration.

We fabricate and characterize carbon-based  lead halide perovskite solar cells composed of a mesoscopic scaffold of metal oxides that is screen printed and infiltrated with a lead halide perovskite precursor solution with a methylammonium cation.(MAPbI3)  We characterize the cells over time to investigate degradation pathways and improve fabrication methods. We measure the current produced by the cells under various illumination conditions as a function of applied bias voltage (IV curves) as well as spatially mapping both the structure and the photovoltaic performance of our cells to track and classify defects using both optical micrographs and Light Beam Induced Current (LBIC) imaging.   Observations of  the spectral response of the cells enables us to determine the External Quantum Efficiency (EQE) of our devices as well.  

In an undergraduate laboratory environment we fabricate and characterize Screen-Printed Mesoporous Carbon Perovskite Solar Cells (CPSCs).  The fabrication is based on pioneering work by Hongwei Han's research group.[1]  We adapt our methods from those developed by Trystan Watson's group [2].  We start with FTO coated glass substrates and laser engrave isolation lines.  We spay coat a compact titania layer followed by screen printing a mesoporous layers of titania (for electron transport), zirconia (for a spacer), and Carbon (for hole transport and a back contact).  A Methylammoina Lead Iodide (MAPbI) perovskite precursor is then inflitrated into the mesoporous layers crystalizing to form the perovskite semiconductor structure.  Silver contact electrodes are added to complete the devices.  The fabrication is performed in an ambient environment and no encapsulations are added to the devices.  Each substrate has 36 devices each with an active area of 0.49 sq. cm.  We have produced over a thousand devices with 4 generations of students in the lab. 

We characterize our devices with a wide range of techniques.  Current Voltage characteristics are measured for all devices.  Hero cells have power conversion efficiencies over 12%.  The devices show negligible hysteresis, and are limited in performance by moderate shunt and series resistances.  New higher conductivity Carbon and Silver ink formualations have been tested with significantly better conductivities that have improved Fill Factors and reduced series resistance.  We observe a variety of spatial defects by both LBIC and optical micrographs in the printing process and do statistical analysis of yields on every run to optimize our initial device performance.  We measure EQEs with peaks approaching 80% for freshly made devcies.

We have performed dark storage shelf life measurements over two years.  While devices still work after two years in dark storage, the performance decreases and defects clearly evolve as seen in our spatial imaging over time.  We also perform light soaking studies of both individual cells and modules of cells in series.  We record not only the IV characteristics and the IV curve evolution, but also the changes in EQE and spatial imaging as a function of light soaking under 1 sun conditions with no encapsulation or UV filtering.  We will present these data and discuss what this says about the degradation of these CPSCs.