Perovskite-silicon tandem solar cells are on the brink of commercialization, with efficiencies skyrocketing in the past 5 years, now being the most efficient two-terminal configuration ever made. Yet, the reliability of these devices is still a big question mark. This is in part due to the short time since their development hindering decade-long tests due to sheer time constraints, but also because there is a lack of established accelerated aging protocols due to a lack of understanding of primary failure modes. In the presentation, I will cover our recent results looking at the perovskite top cell and how nanometric defects (1) - how they trigger device degradation and how they can be mitigated – but also at effects on the um- and cm-scale, such as how the choice of the silicon cell texturing affects performance and stability (2), as well as long-distance ionic effects (3,4).

1. Othman et al., Adv. Mater. 2024, accepted
2. Turkay et al., submitted
3. Artuk et al., submitted
4. Jacobs et al., Energy Environ. Sci., 2022,15, 5324-5339

Metal halide perovskites have demonstrated exceptional properties for various technological applications. However, several challenges still impede their full commercial expansion. From a sustainability perspective, this communication reviews the current status of some of the most significant challenges and, in certain cases, offers potential solutions.

One of the key challenges is the toxicity associated with materials, precursors, and solvents. This issue has gained increased relevance following the publication of the Safe and Sustainable by Design Framework in Europe.[1] The adoption of deposition techniques other than spin-coating presents new difficulties for improving efficiency, but it also offers considerable opportunities for reducing energy consumption and waste from an environmental and economic sustainability perspective. Nevertheless, significant technological optimization is still needed, particularly in the selection of green solvents and their optimal drying and recycling processes.[2]

Techniques such as hot injection and microwave synthesis for producing perovskite nanoparticles also face notable challenges in scaling, enhancing performance, improving energy efficiency, and increasing circularity. Another limiting factor affecting commercialization is the criticality of materials in Europe and other countries, particularly metals like cesium,[3] rubidium, antimony, and bismuth.[4] Beyond their inclusion in official lists, the issue is more complex and intriguing when we consider the dynamics of systems, including global resource availability and the geopolitical factors that influence them.

Additionally, we present findings from environmental impact studies employing life cycle analysis methodology on metal halide perovskites, highlighting unresolved issues related to inventory shortages and deficiencies, the lack or obsolescence of toxicity characterization factors for certain substances (such as metals and solvents), and the unknown behavior of nanoparticles in ecosystems and their effects on human health.

Finally, the silicon photovoltaic technology has yet to resolve the issue of what to do with solar panels at the end of their life cycle. We should not allow metal halide perovskites to face the same fate. We still have the opportunity to adopt circular practices from this early stage of research, including mechanisms like recent digital product passports.

This presentation aims to stimulate discussions, exploring innovative solutions and collaborative efforts to address these pressing challenges in the sustainable development of perovskite technologies.

In recent years, remarkable progress has been made in the field of metal halide perovskite solar cells, resulting in power conversion efficiencies (PCE) surpassing 26%. These advances are made possible by compositional and additive engineering of the perovskite active layer and the development of more efficient charge extraction layers. Most research efforts are dedicated to processing perovskites from solution, often from highly toxic solvents such as dimethylformamide (DMF). While this is manageable for lab-scale fabrication, using such solvents raises considerable safety and environmental concerns about fabricating perovskite devices on a mass scale. To solve this challenge, green solvents suitable for perovskite processing must be identified, and perovskite deposition processes must be adapted to the properties of the new solvents. Alternatively, solvent-free deposition methods must be developed that are compatible with industry processing on a large scale. In this talk, I will present promising green solvent alternatives to DMF and highlight recent developments in vapor-based deposition methods of metal halide perovskites.

Today, hybrid halide perovskite solar cells show high power conversion efficiencies (PCE >25%), but volatile organic cations (MA⁺, FA⁺) can limit their thermal stability. Therefore, inorganic perovskites such as CsPbI₃ appear as promising materials for perovskite PV devices ^[1]. In addition, their band gap, around 1.7 eV, is close to the ideal one for perovskite-on-silicon tandem applications. The inorganic perovskites are considered as good candidates for the development of stable and efficient single junction and tandem solar cells.

Despite many obvious advantages, the PCEs achieved with inorganic CsPbI₃ perovskites remain lower than those of their hybrid counterparts. The difference is mainly due to the difficulty of synthesising a stable CsPbI₃ perovskite phase. According to Goldschmidt tolerance factor calculations, CsPbI₃ is just at the limit of forming a stable perovskite phase due to the relatively small size of Cs⁺ cations compared to MA⁺ or FA⁺ cations. Therefore, the simultaneous formation of non-perovskite phases is often observed during the synthesis of CsPbI₃.

Here, we present our strategy to develop inorganic perovskite as an absorber, deposited by slot-die coating in ambient atmosphere, a relevant industrial large area deposition technique that has not yet been explored for this type of perovskite.

Firstly, we focused our attention on the ink preparation to obtain stable inorganic perovskite films. After investigating several additive strategies, dimethylammonium iodide (DMAI) ^[2] was chosen to stabilise CsPbI₃. Several parameters of the precursor solution such as the additive concentration and solvent ratio were further optimised. Furthermore, the composition was tuned by adding bromide ^[3]. Secondly, using this ink, the deposition of the inorganic perovskite thin film by slot-die coating, in ambient atmosphere, was optimized. Deposition parameters were refined based on morphological, structural, and optical characterizations of the deposited inorganic perovskite layers. Uniform thin films with a surface area of up to 5x10cm² were obtained (Fig.1).

Finally, to test our developed thin films, we implemented the optimised inorganic perovskite absorber in solar cells. A PCE of the same order of magnitude as the PCE obtained for solar cells deposited by spin-coating in ambient atmosphere on a small surface area of 2.5x2.5cm² was obtained on 5x10cm² (Fig.2). After further optimisations, we obtained a maximum power conversion efficiency of 12.7% for solar cells containing inorganic perovskite deposited by slot die coating in ambient atmosphere.

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 with the proper additives and encapsulation Sn-based halide perovskites can increase significantly their stability allowing their efficient application in tin iodide perovskite solar cells. Nevertheless, as in the case of Pb-based halide perovskite the potential applications of tin-perovskites is not limited to photovoltaic devices. In addition, we report the use in Sn-based LEDs, photodetectors and to drive photocatalytical reactions. 

The commercial success of perovskite solar cells (PSCs) depends on transitioning from lab-scale fabrication to high-throughput, low-cost manufacturing. Roll-to-roll (R2R) processing presents an ideal route, offering continuous production with reduced material waste. However, the shift from batch processing to fully inline deposition introduces challenges in coating uniformity, interlayer compatibility and defect control. These issues must be addressed to unlock the full potential of perovskites for industrial-scale photovoltaics.

This talk will provide a broad overview of R2R deposition strategies for PSCs, focusing on SnO₂ electron transport layers, PEDOT and SAM-based hole transport layers, perovskite absorber layers, P3HT, and solution-processed carbon electrodes. A key emphasis will be on scalable approaches to layer deposition, particularly slot-die coating, and how solvent engineering and interfacial adhesion strategies can overcome the challenges of high-speed perovskite module fabrication. Recent advancements in fully solution-processed electrode deposition will also be discussed, particularly the replacement of evaporated metal contacts with carbon-based alternatives, demonstrating a pathway toward fully printed, low-cost, and highly stable PSCs.

Looking ahead, building on our existing work on registration-based interconnects, we aim to explore laser-patterned interconnects as a route to improving module performance while reducing processing complexity. The next steps also include integrating real-time quality control and inline lamination of encapsulation layers to further enhance the scalability and long-term stability of R2R perovskite module manufacturing. These developments will be critical for bridging the gap between laboratory-scale advances and commercially viable roll-to-roll perovskite solar production.

One of the major drawbacks of lead halide perovskites and an obstacle to their commercialization is their lack of long-term chemical and structural stability. When exposed to external stressors, these materials either chemically degrade or structurally transform into other crystal phases. Understanding the end-of-life mechanisms of perovskites is essential for developing better strategies to prevent their degradation and enable reversible process for re-manufacturing thin films and devices. I investigated the synergistic role of humidity and oxygen in the degradation pathway of lead halide perovskites used in solar cells. This was achieved using synchrotron-based in-situ grazing-incidence wide-angle X-ray scattering (GIWAXS) and X-ray photoelectron spectroscopy (XPS) (Hidalgo et al., J. Am. Chem. Soc. 2023). This initial work highlighted the interplay between structural changes and surface chemical reactions in lead halide perovskites, leading to the evaluation of a surface passivation strategy and compositional engineering, resulting in more durable lead halide perovskites for photovoltaic applications.

Perovskite solar cells (PSCs) hold great potential as technology for the next generation of thin-film photovoltaics. However, industrial-scale fabrication processes must be significantly improved for PSCs to become commercially viable. Scalable solution deposition techniques, such as slot-die(SD)-coating, are difficult to control during the entirety of the perovskite thin-film formation, because of complex fluidics, drying, and crystallization dynamics during high solvent removal. Drying with a narrow gas-purged slot-jet is an established drying method that provides a sufficiently high solvent mass transfer to remove the solvent from the wet thin-film, inducing a prompt nucleation. In prior studies, a model on drying dynamics of perovskite thin-films enhances the understanding of the complex drying process, analyzing impacts of gas-flow velocity and web speed from a fundamental view point^[1;2]. Moreover, we validated the model on large-area substrates, predicting drying windows by in-situ monitoring of SD-coated thin-film drying processes^[3]. The results lead to concrete rectification work on the drying procedure, enhancing the optimally dried area. However, slot-jet-drying still comes with inhomogeneous fluidic dynamics and disturbed gas flows, causing unintended fluidic backflows, non-uniform drying patterns and severe edge effects, impeding progress for perovskite/silicon tandem solar cells (TSCs). Hence, there is need to investigate and optimize the formation of polycrystalline perovskite thin-films fabricated via scalable deposition methods.

In response, we address the necessity for precise drying conditions, enhancing the quality of perovskite thin-films through i) a novel convection-drying method, advancing the homogeneity of the drying process of SD-coated solution thin-films on the entire area, and ii) an adjusted material composition strategy for 2-step processed SD-coating, leading to higher operational stability. Specifically, we introduce a gas-assisted-drying system that provides uniformly distributed drying rates for SD-coated, 2-step processed triple-halide perovskite wet thin-films. Precisely defined drying conditions are established using a stationary, gas flow-controlled two-dimensional nozzle array pattern, consisting of impinging jets and surrounded by suction holes for local solvent removal. This design enables precise control of drying rates. The specific drying system used in this work is inhabited in an in-house glovebox system, meaning the drying circle is fully integrated into the inert atmosphere.

We systematically evaluate and compare the implemented novel drying strategy with established slot-jet-drying by fabricating SD-coated PSCs with alternative drying approaches over an area of 100 cm² with all scalable techniques. Remarkably, we successfully demonstrate the correlation of applied process parameters at exact sample positions with the resulting thin-film morphology, grain size distribution, and optoelectronic properties, resulting in PSCs with efficiencies up to 19.6% and high PCE-yield of >90% on the entire substrate. We validate an enhanced area utilization with 5x5 cm² solar mini-modules on the quadrants of 10x10 cm² substrates, each reaching a PCE ≥17.6% (17.7% ±0.2%). The results imply high homogeneity during the coating and drying processes, with only minimal relative upscaling loss due to module scribing and interconnection resistances, outlining the relevance of our scaling methodology. Consequently, we employ the drying method to a material composition suitable for tandem applications (E_g ~1.68 eV) based on a work of Pappenberger et al^[4]. We demonstrate TSCs with PCEs of up to 24.6%, fabricated with all scalable techniques. Particularly, the successful fabrication of TSCs (mean PCE ~24.0%) with a homogeneous PCE distribution of ±0.7%, confirms the importance of a systematically controlled drying technique within an optimized 2-step process. This work underlines the necessity of precise control as well as an understanding of drying dynamics being vital to facilitate large-scale solution-based high-quality optoelectronic thin-films consistently.

Our full research paper“Spatially Regulated Gas Flow Control for Drying of Large Area Slot-Die-Coated Perovskite Thin-Films”by Kristina Geistert et al. is in preparation.

Metal halide perovskites are gaining attention in detectors of high-energy photons, showing potential in thin-film dosimetry as well as imaging, the latter when prepared as single crystals. Typically, perovskites are made from solutions of the halide salts precursors, which might represent a challenge towards scalability and substrate integration. Here we will discuss dry synthetic methods for the fabrication of perovskite photodetectors. Perovskite thin-film detectors can be made using physical vapor deposition (PVD), an established industrial method. PVD allows for high-purity films with controlled thickness and easy integration into multilayer devices. We present PVD-based detectors with low dark and noise currents, stable reverse bias, and X-ray sensitivity >30 μC/Gy/cm². For thick perovskite materials, we introduce a dry method to prepare free-standing perovskite-polymer composite disks, tunable from 25 to 250 μm in thickness. These composites can be laminated onto rigid or flexible substrates, creating functional detectors with high environmental stability and promising limit of detection.

Metal halide perovskite (MHPs) solar cells represent a promising newcomer in the front of emerging photovoltaic technologies, therefore a potential player to challenge the dramatic energy crisis and climate change that we are facing. The exceptional properties of MHPs derive from their hybrid organic-inorganic nature, which allows also for low-cost and straightforward processing. Solar cells containing MHPs as absorbing layer have already achieved a power conversion efficiency above 26,5 %, close to the efficiency of silicon-based devices. Nevertheless, a major limitation, still preventing the uptake of the technology, is related to the reduced stability of these devices when exposed to operative conditions, namely temperature, light, and moisture. Herein, an effective defect passivation of MHP surfaces is a key strategy to tackle both the stability and the enhancement of solar cell performances. Although many solution-based approaches have been tested, we have explored in the last years an innovative use of plasma, as a solvent-free, scalable, industrially available and non-invasive processing to enhance MHP solar cells performances [1]. The effect of cold plasmas fed by gases as Ar,  ,  and  both on lead-based (MAPbI3) [2] and lead-free (FASnI3) [3] perovskites was investigated in terms of optochemical and morphological modifications and correlated to the performance of the photovoltaic devices. An interesting improvement in power conversion efficiency (PCE) was observed for the Ar-treated MAPbI3 perovskites, ascribed to a modulation of surface defects, while a newsworthy suppression of the intrinsic tendency of tin (II) to oxidize to tin (IV) was obtained for the N2-plasma treated FASnI3 perovskites. Starting from these encouraging results, further surface plasma processes have been investigated [4], among which the promising treatment with sulfur-containing molecules, proved to obtain a good passivation of surface defects, through the formation of Pb-S bonds, allowing the improvement of both the fill factor and the PCE of the investigated solar cells, opening new applicability scenarios for these plasma-based processes [5]. 

References:

[1] V. Armenise, S. Covella, F. Fracassi, S. Colella, and A. Listorti, ‘Plasma‐Based Technologies for Halide Perovskite Photovoltaics’, Solar RRL, 2024, doi: 10.1002/solr.202400178.

[2] A. Perrotta et al., ‘Plasma-Driven Atomic-Scale Tuning of Metal Halide Perovskite Surfaces: Rationale and Photovoltaic Application’, Solar RRL, 2023, doi: 10.1002/solr.202300345.

[3] S. Covella et al., ‘Plasma-Based Modification of Tin Halide Perovskite Interfaces for Photovoltaic Applications’, ACS Applied Material & Interfaces, 2024, doi: 10.1021/acsami.4c09637.

[4] V. Armenise, S. Colella, A. Milella, F. Palumbo, F. Fracassi, and A. Listorti, ‘Plasma-Deposited Fluorocarbon Coatings on Methylammonium Lead Iodide Perovskite Films’, 2022, doi: 10.3390/en15134512.

[5] S. Covella et al., manuscript in preparation.

In the past decade, the efficiency of lead halide perovskite-based solar cells has reached levels comparable to those of established silicon solar cells. This advancement makes perovskite solar cells (PSCs) particularly promising for future commercial applications. However, challenges such as long-term stability and scalability still need to be addressed before they can be commercially viable. Additive engineering is one approach that holds the potential for overcoming these challenges.

In this study, we presented a novel additive engineering approach for the formation of FAPbI₃ perovskite layers by vapor deposition. The approach is based on a two-step deposition process in which PbI₂ is vaporized together with additives. We found using SEM, XRD, UV-vis, and XPS that the additives significantly improve the efficiency of the precursor conversion process to FAPbI₃ and lead to an improved microstructure of the perovskite films. When integrated into p-i-n solar cells without interfacial modifications, FAPbI₃ layers achieve an efficiency of 18.34%, which is significantly superior to devices fabricated without additive engineering.

Metal halide perovskite semiconductors have shown significant potential for use in photovoltaic (PV) devices. While fabrication of perovskite thin-films can be achieved through a variety of different techniques, thermal vapour deposition is particularly promising, allowing for high-throughput fabrication and large-scale production[1]. However, the ability to control the nucleation and growth of these materials, particularly at the charge-transport layer/perovskite interface, is critical to unlocking the full potential of vapour-deposited perovskite PV[2].

In this study, we explore the use of a templating layer to control the growth of co-evaporated perovskite films, and find that such templating reproducibly leads to highly oriented films with identical morphology, crystal structure, and optoelectronic properties, independent of the specific substrate on which the perovskite was deposited[3]. When incorporated into solar cells, devices based on this approach showed reproducible improvements, yielding vapour-deposited FA_0.9Cs_0.1PbI_3-xCl_x solar cells with steady-state solar-to-electrical power conversion efficiencies over 19.8%. Our findings provide a straightforward and reproducible method of controlling the charge-transport layer/perovskite interface in vapour-deposited perovskite solar cells, further clearing the path toward large-scale fabrication of efficient perovskite optoelectronic devices.

In this work, we analyse the photoemission of lead halide perovskite quantum dots synthesized within nanoporous metal oxide films with either electron scavenging (such as TiO₂) or electron blocking (SiO₂) properties as a function of the excitation power density. In good agreement with previous reports [1-3], at low excitation fluences, scaffolds that facilitate charge extraction from the perovskite electronic bands, such of TiO₂, give rise to a lower emission intensity and quantum yield (QY) with respect to more insulating ones like SiO₂. Counterintuitively, the situation reverses under higher irradiation fluences, for which electron scavenging scaffolds favours a highly intense amplified spontaneous emission (ASE) from perovskite quantum dots. This effect is understood by analysing the interplay between the efficiency of carrier transfer to the matrix and the different electronic processes occurring at each irradiation stage, i.e., trap-assisted and band-to-band recombination at lower and intermediate fluences, and the competition between Auger recombination and population inversion at higher ones. These findings open the path to develop highly efficient light emitting perovskite QD films, leading future progress for their potential application in advanced photonic devices.

Water exposure is typically associated with adverse effects on the structural integrity and photoluminescence of lead halide perovskites, often hindering their performance in optoelectronic applications. Nevertheless, we report a humidity-induced process for the in situ synthesis of CsPbBr₃ nanocrystals (NCs) within a magnesium acetate matrix, achieving an outstanding near-unity photoluminescence quantum yield (PLQY).

Moreover, the process is facilitated by the controlled introduction of water in combination with pH modulation via an acetic acid/acetate buffer system. This setup generates hydroxide ions (OH⁻), which passivate electronic trap states within the CsPbBr₃ NCs, further enhancing their optical stability and efficiency.

By transforming water exposure from a destructive factor into a beneficial tool, this method represents a novel paradigm in perovskite chemistry as an advanced strategy to improve the stability and performance of lead halide perovskites through precise water and pH control.

Our approach showcases remarkable optical properties, boasting a near-unity PLQY alongside exceptional reproducibility and repeatability under low-demanding process conditions. Its greatest advantage lies in its exceptional versatility and compatibility with high-throughput roll-to-roll printing techniques, enabling the fabrication of cost-effective, large-area, and high-performance devices. As a result, this approach has the potential to significantly reduce costs, improve sustainability, and expand applications across various light-emission technologies, such as down-conversion and gas sensing.

Ion migration in halide perovskites and its relation with the external contacts has very important implications in solar cells, photodetectors, X-ray detectors and memristors.¹ Ion migration poses a negative effect in some optoelectronic applications controlling the hysteresis and the long term stability. Here we discuss the effect of the dimensionality of the crystalline structure of halide perovskites in relation to the ion migration and the connection with stability of solar cells.¹  Alternatively, the stability can be enhanced by an adequate selection of the external contacts to be compatible with the migrating ions. On the other hand, the ionic conductivity of halide perovskite is responsible for a memory effect that can be used in resistive memories expanding the applications for this type of materials.  Several configurations are  evaluated in which structural layers are modified systematically: formulation of the perovskite including 2D perovskites,² the nature of the buffer layer³  and the nature of the metal contact⁴. We show that in order to efficiently promote migration of metal contact the use of pre-oxidized metals greatly enhance the performance of the memristor and reduces the energy requirements. Importantly, these halide perovskite devices show potential in both volatile and non-volatile memristive devices that find applications in neuromorphic computing.⁵ Overall, the interplay between migrating ions and chemical interactions with the contacts can be extrapolated to the different optoelectronic devices fabricated with halide perovskites.

Material and technological research in neuromorphic computing has garnered significant attention in recent years, with numerous examples of memristors serving as simple electrical synapses. In addition to electrical input and output, light is increasingly used as both an input and output signal in optical memristors, where light transmission is modulated.

In my talk, I will introduce a new concept for an optical memory device based on photoluminescence, termed the "memlumor"—a luminophore with memory.[1] The photoluminescence quantum yield of a memlumor "remembers" the history of previous excitations through parameters governing its photophysics and photochemistry. Metal halide perovskites have proven to be highly promising materials for memlumors. We demonstrated the synergetic coexistence of both volatile and non-volatile memory effects in perovskites over a broad timescale, ranging from nanoseconds to days.[1] We identified the origin of this complex response as the phenomena of photodoping and photochemistry triggered by light input, both of which are closely tied to defect states and their photoinduced dynamics.[2] Remarkably, defects and their temporal dynamics—typically viewed as detrimental to device performance—are essential for memlumor operation.

I will showcase the memlumor properties of CsPbBr₃, which exhibits memory effects over timescales from nanoseconds to minutes, with switching energy as low as 3.5 fJ. Additionally, I will discuss a novel method of multi-pulse time-resolved photoluminescence,[3] specifically suited to study trapped charge carriers in luminescent semiconductors and memory effects induced by them.

Memlumors, as novel optical dynamic computing elements, have a potential to provide a new dimension to existing optical technologies, paving the way for their application in photonic neuromorphic computing.

Halide perovskite memristors exhibit excellent properties for neuromorphic computing including analog resistive switching, endurance, and low power requirements. However, the reproducibility and stability are limiting factors for the practical application of these devices. Recently, our research group demonstrated that introducing an interfacial buffer layer between the metal contact and the perovskite active layer can improve the stability of the halide perovskite memristors and even modify the activation mechanism [1, 2]. Nevertheless, the mechanisms through which these devices work remain unclear, and a deeper understanding is required to achieve a rational optimization.

In this work, we present the fabrication of highly reproducible memristors using Ag as active electrode, a highly stable perovskite formulation (MAPbBr₃), and a buffer layer containing oxidized silver (AgI). These memristors show high reproducibility in fabrication and stability (>10⁴ cycles of pulse trains) [3]. This highly reliable system enabled an in-depth study of the mechanisms operating in perovskite memristors, which provided insights into the nature of the dual volatile and nonvolatile responses. Short-duration pulses at the activation voltage lead to a two-state volatile response due to the formation of an ionic double layer close to the contacts, which returns to the initial state once the bias ceases. In contrast, long-duration pulses lead to a gradual increase in current and a nonvolatile response caused by the appearance of a chemical inductor. The observed multi-state nonvolatile regime is related to the formation of Ag⁺ conductive filaments and provides suitable conditions for analog computing. Overall, we provide a clear understanding of the nature of these two operating regimes in halide perovskite memristors and show the tools to investigate them in other systems.

Polarizers are ubiquitous components in modern optoelectronic devices  including displays and photographic cameras. However, achieving efficient control of light polarization remains an unsolved challenge. The main drawback of the existing display technologies relies on the substantial optical losses due to the use of polarizers for generating polarized light. In this context, organometal halide perovskite (OMHP) nanostructures offer a promising solution owing to their tunable optical properties—including adjustable bandgap, photoluminescence, and efficient light emission with minimal non-radiative recombination.^[1–3] Their outstanding electrical properties have elevated hybrid perovskites as the material of choice in photovoltaics and optoelectronics. Among the different OMHP nanostructures, nanowires and nanorods have lately arisen as key players in controlling light polarization for lighting or detector applications.

In this work,^[4] we propose applying an evolved version of the vacuum technique Glancing Angle Deposition (GLAD) as an advanced alternative to synthesising anisotropic-supported OMHP nanostructures. Our approach is a two-step fabrication procedure consisting of the room temperature deposition of PbI₂ at glancing angles, followed by deposition of CH₃NH₃I at normal incidence (0º). As a result, highly anisotropic perovskite nanostructures resembling “nanowalls” have been fabricated. Such alignment degree endows the samples with anisotropic optical properties such as UV-visible absorption and photoluminescence. Moreover, their implementation in n-i-p solar cells can be used to develop self-powered polarization-sensitive photodetectors along the visible range. Thus, the use of Glancing Angle Deposition yields OMHP nanostructures with high anisotropy, controlled microstructure, and thickness, demonstrating potential for scalable, large-area fabrication. This technique is fully compatible with microelectronic and optoelectronic processing methods including CMOS and roll-to-roll technologies, which opens the path towards developing tuneable anisotropic optoelectronic devices based on OMHP.

Hybrid-halide perovskites exhibit a unique combination of electronic and ionic characteristics, with the latter posing significant challenges to understanding and controlling the operational mechanisms of perovskite devices. The movement of ions within these materials can lead to issues such as recombination, photovoltage losses, and instability. To address these detrimental effects, various strategies have been employed with notable success. However, the fundamental mechanisms underlying these strategies often remain obscured.

A key distinction between electronic and ionic charges lies in their temporal dynamics: ionic responses are significantly slower, involving processes that occur over extended time frames. Impedance spectroscopy (IS) spans a wide range of time scales, enabling the separation of contributions from different components and processes within the device. In fact, at lower frequencies, IS can yield valuable insights into ion dynamics and their influence on electronic performance by quantifying resistances and capacitances. A notable feature often observed in this frequency range is the "loop" or inductive behaviour. Although the precise origin of this phenomenon is still under debate, its associated time constant can reveal crucial information about the kinetics at the interfaces and their effects on the bulk material.

This contribution will focus on quantifying this time constant and its implications for understanding perovskite device performance. We will explore the relationship between this inductive behaviour, the mechanisms behind a record photovoltage of 1.65 V achieved by a bromine-based perovskite solar cell (PSC), the role of a self-assembled monolayer in enhancing the stability and open circuit potential of a PSC, and insights into the electroformation process of a perovskite-based memristor. These examples illustrate how impedance spectroscopy can offer crucial insights to untangle the complexities of the perovskite puzzle and address its technological challenges.

The conceptual idea of the integration of energy photovoltaic (PV) generation and storage systems in a single unit, the photocapacitor, offers an innovative approach to manage energy supply for IoT systems that typically requite low power and work under discontinuous illumination, improving the system performance, reducing device size and weight. Several photovoltaic technologies (Silicon, Dye Sensitized, Organic and Perovskite solar cless) and type of supercapacitor have been integrated in four, four, three and two terminal photocapacitor, leading so far to a maximum device efficiency of 25% for a perovskite based photocapacitor measured under 1 sun illumination [1].

In this presentation I will introduce the concept of photocapacitor, highlighting the working principles, the characteristic features and potentiality of this type of device. I will then show our work on the realization of perovskite based photocapacitors both on rigid and on flexible substrates.

In particular I will report on the all printed three-terminal photocapacitor based on carbon perovskite solar cell (CPSC) integrated with an MXene-based in plane microsupercapacitor (MSC) realized on glass substrate. The device was characterized both under 1 sun and at 1000 lux illumination achieving an overall efficiency of 3.8% with a striking 99% coulombic efficiency and 87% capacitance retention over 6000 cycles for the supercapacitor unit.

I will then show the integrated two terminal flexible photocapacitor, where a flexible perovskite solar module was integrated with flexible interdigitated supercapacitors interconnected in parallel and series with peak overall and storage efficiencies of 2.8% and 23% respectively. Finally I will show some applications of those devices [2].

The synthesis of ABX₃ quantum dots (QD) using a mesoporous material with a narrow pore size distribution is a preparation method that has gained interest in recent years due to the ease of processing and the excellent optical properties of the QDs obtained in the pore network.[1] These ligand-free QDs also present a pristine surface that is suitable for interacting with the surrounding atmosphere. In this work, we have synthesized CsPbBr₃ QDs within the pore network of high optical quality SiO₂ porous films. We analyzed the variation of the QDs luminescence response under the gradual exposure to vapors, since the mesostructure of the matrix determines the rate at which vapor molecules will adsorb onto the pore walls and eventually condensate, filling the void space.[2] These results open the route to apply ABX₃ QDs in base materials for sensing.   On the other hand, the aforementioned control of the water adsorption allowed us to obtain an intense and enduring blue emission (470-480 nm), with a photoluminescence quantum yield (PLQY) of 40% when Cs₄PbBr₆ was previously embedded in SiO₂ porous matrix.[3] This blue emission originates from very small CsPbBr₃ nanocrystals (diameter<3nm) formed by the controlled exposure of Cs₄PbBr₆ to humidity.

The power conversion efficiency (PCE) of silicon-based solar cells is rapidly approaching its practical limit of 29%,[1] highlighting the need for alternative absorber materials. Emerging photovoltaic materials such as hybrid halide perovskites (HHPs) have shown to be a good alternative to silicon due to their high PCE (26.7%) as well as low-cost solution-based processing methods.[2], [3]

In order to understand the impact of the precursor solution in a device processed from solution, it is necessary to gain an insight into how the precursors affect the early stage of crystallisation. To have a better understanding of the role of the solvent in HHPs precursor solutions, we investigated MAPbI₃ precursor solution in γ-butyrolactone (GBL), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP) and mixtures thereof using small angle X-ray scattering (SAXS).

SAXS is a non-destructive technique based on the scattering length density difference between the scattering objects and the matrix. SAXS allows us to determine the average distance between the scattering objects, their size and shape as well as the interaction with each other.[4] We performed SAXS experiments at HZB synchrotron radiation source BESSY II at the four-crystal monochromator beamline[5] of the Physikalisch-Technische Bundesanstalt using the ASAXS endstation.[6]

All the SAXS patterns obtained from the measurements show a clear maximum in the scattered intensity at q-values between 2.7 and 3.8 nm^-1 (values for GBL and DMSO respectively), a peak in the SAXS pattern is an indication of the presence of agglomerates in solution. The average distance between the scattering objects (d_exp) varies depending on the solvent used, showing that the solvent must be part of the scattering objects. In a previous study[7] we showed that the scattering objects in solution have a core-shell configuration, with a solvent shell surrounding a [PbI₆] core, which can be arranged as a single octahedron or as corner-sharing octahedra. In this study, we show that solvents with high donor number (DN), such as NMP or DMSO, present a lower d_exp compared to DMF and GBL. This indicates that solvents with high DN favour the single octahedron arrangement in the core. The results obtained from the analysed SAXS data (using SASfit[8]) indicate that solvents with high DN favour monodisperse solutions, i.e. all the scattering objects have the same size. DMF and GBL favour polydispersity, which follows a lognormal size distribution. This is in agreement with the proposed core-shell model since having only a single octahedron in the core can explain the monodispersity in high DN solvents.

We will discuss how the nature of the solvent influences the arrangement of the precursors in the precursor solution since it has the potential to impact the crystallisation process of the HP and, therefore, the performance of a device produced from solution processing.

Metal halide perovskites are at the forefront of next-generation optoelectronics due to their exceptional optoelectronic properties and ease of processing. However, challenges in scalability, stability, and process reproducibility remain critical barriers to their commercial adoption. In this work, we present the baseline we established for slot-die coated perovskite solar cells in the HySPRINT lab of HZB for small area test cells reaching up to 22% PCE collaboratively. We recently established a digital workflow collecting most relevant data regarding the fabrication of solar cells as well as their performance in the research data management platform NOMAD. We demonstrate how digital tools can greatly enhance intra-lab collaboration and will showcase how these kind of platforms can also be used for research data sharing by the wider research community.

We demonstrate the integration of in-situ process monitoring techniques, such as photoluminescence, during slot-die coating. These tools provide immediate feedback on critical parameters, including film thickness, drying kinetics, and phase evolution, enabling precise control over film quality and reproducibility. Data is complemented by in-situ process monitoring experiments using GIWAXS at the BESSY synchrotron.

Finally, we present an example of the fabrication of perovskite solar cell mini-modules using scalable methods, achieving efficiencies exceeding 20% with enhanced stability under operational conditions. The insights gained from these studies pave the way for the large-scale manufacturing of stable and efficient perovskite devices, addressing key technological challenges and supporting the field’s transition from laboratory to market.

Electrochromic materials are garnering attention for applications in smart windows, displays, and augmented reality, enabling energy-efficient solutions by modulating light and heat transmission.[1]-[6] Hybrid organic-inorganic halide perovskites, renowned for their exceptional optoelectronic properties, have recently been explored for their electrochromic behavior. This study investigates perovskite precursor solutions as electrochromic materials, offering a promising alternative to conventional approaches that integrate perovskite solar cells with separate electrochromic layers. The perovskite precursor solution exhibits a voltage-dependent color change from yellow (0 V) to reddish-brown (2.5 V). The device achieves a 22% transmittance drop at 500 nm, with an average visible transmittance variation of ~30%, ideal for smart windows and display technologies. Raman and UV-Visible spectroscopy provides an insight into the mechanism and modifying A-site cations, B-site cations, or X-site anions in the perovskite structure further tunes the electrochromic properties. Demonstrations include a 4 cm² electrochromic window and a 24 cm² display incorporating a perovskite gel mixture, with response and recovery times of 7.65 s and 28.25 s, respectively. The system shows stable cyclic performance, a coloration efficiency of 1.084 cm²/C, and significant potential for energy-efficient applications. This study highlights the novel electrochromic behavior of perovskite solutions, eliminating the need for integrating solar cells with external electrochromic materials. The findings advance the development of scalable, sustainable devices for smart windows and displays, paving the way for innovative, energy-efficient technologies.

Over the past decades, three-dimensional hybrid perovskites (HPs) have gained prominence in optoelectronics, extending beyond traditional photovoltaic applications. Their versatile potential as light-emitting diodes, photocatalysts, and photodetectors positions them as key candidates for efficient, low-cost, and flexible photonic devices. Among HPs, methylammonium lead iodide (MAPI) has continued to attract interest due to its broad application potential, where defect engineering plays a crucial role in tuning its intrinsic properties. Notably, the synthesis method significantly influences the defect landscape and, consequently, the performance of MAPI. 

In this work, we present a solvent-free mechanosynthesis approach to produce MAPI [1] in large quantities for electromagnetic wave absorption (EMWA) studies—a very seldom investigated application for HPs [2]-[4]. Our results reveal that 4 h-ball-milled MAPI (MAPI4h) powders with a powder size lower than 20 µm exhibits a significant improvement of dielectric loss at 11.4 GHz within the X-band frequency range (8–12 GHz) compared to powders ball-milled for only 30 minutes (MAPI30). The enhanced performance of MAPI4h is attributed to improved dipole polarization relaxation and reduced particle sizes.

Structural characterizations of MAPI4h confirm the preservation of the expected I4/mcm crystalline structure of MAPI with no apparent bulk defects but revealed smaller grain and crystallite sizes and increased strains in comparison with MAPI30. A fractal microstructure has been evidenced with aggregated grains constituted of nanograins and these aggregates form agglomerate of aggregates with different sizes. In addition, an orientation of nanograins inside grains of MAPI30 is evidenced when in MAPI4h, this oriented nanograins aggregation could be extended between the adjacent grains due to prolonged milling and localized temperature increases. Detailed defect analysis through static and time-resolved photoluminescence, Urbach energy calculations, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy-energy-dispersive X-ray spectroscopy (HRTEM-EDXS), and positron annihilation lifetime spectroscopy (PALS) highlights significant surface modifications with a raise of surface vacancy-type (MA⁺ and I^- vacancies) defect level in MAPI4h powders (<20µm). PALS, in particular, identifies the presence of specific open defects in MAPI that differ from those earlier observed in MAPI layers or single crystals prepared by solution or dry processes. A density peak in the defect distribution is located at a mean depth of about 55.9 nm from the surface of the first layer of monocrystalline grains. Its existence suggests that the defect population results from competitive reaction of generation and recombination where the grain surface plays a role of sink. The density peak tends to increase with longer grinding time.

These surface vacancies in MAPI4h behave as dielectric polarization centres by stabilizing methylammonium dipoles, which results in enhanced dipole polarization relaxations. The heterogeneous interface between the bulk MAPI and the modified surface could largely enhanced the interfacial polarization of EMWA material, improving dielectric loss [5]. Additionally, the improved dispersion of sub-20 µm powders within polymeric matrices and high specific surface area exhibiting more surface defects enable stronger particle-wave interactions during EMWA testing. These synergistic effects, driven by surface defects and structural optimization, resulted in promising EMWA properties. 

This work emphasizes the potential of mechanosynthesis to tailor defects in hybrid perovskites, providing a pathway to explore defect-driven properties and expand their applications beyond optoelectronics.