Layered (2D) hybrid organic-inorganic halide perovskites have emerged as promising semiconductors in optoelectronics. These materials consist of halide perovskite slabs templating organic moieties, offering unique optoelectronic properties and the ability to self-assemble into well-organized structures via solution-processing or mechanosynthesis of powders. Despite their potential for applications in optoelectronics, such as solar-to-electric energy conversion in photovoltaics and systems for neuromorphic computing, their performance is inferior to that of 3D perovskite analogues. This is mainly due to the electronically insulating nature of organic moieties, which impedes charge transport in functional devices. However, the tunability and self-assembly of these hybrid materials present opportunities to enhance their optoelectronic properties and establish a novel platform for templating functional photochemical transformations.This project aims to utilize layered (2D) perovskites as hybrid organic-inorganic scaffolds for templating photochemical transformations within the organic spacer layer, enhancing their optoelectronic properties and expanding their applications in modern optoelectronics. Specifically, the focus will be on integrating light-responsive polyaromatic molecular systems into the hybrid 2D perovskite framework that are capable of photopolymerization, photocyclization, or photoisomerization upon light irradiation, enabling photochemical transformations that are otherwise challenging or inaccessible in the solid state. As a result, the photoinduced transformations will not only improve the charge transport through the organic layer, thereby enhancing the optoelectronic characteristics of the hybrid materials, but also enable the development of multi-state switching in memory elements for neuromorphic computing.This will be accomplished through the complementary expertise of three research partners, namely the IChO PAS in Poland (synthesis of polyaromatic compounds and their applications, such as in singlet fission), HUN-REN TTK in Hungary (synthesis and characterization of light-responsive molecular systems), and EPFL/AMI in Switzerland (fabrication and characterization of hybrid perovskite materials and devices, complemented with photochemical characterization). Our approach will integrate various techniques, encompassing molecular and material synthesis, comprehensive characterization, and device application. This innovative approach will introduce novel concepts for templating photoinduced transformations in hybrid materials, unlocking new functionalities to propel advancements in modern optoelectronics.

SolarGuard is a 3-year project targeting innovation in the field of photovoltaic (PV). Its overarching objective is to develop the materials and the processes for the mass-manufacturing of heterojunction (HJT) and TOPCon solar cells and modules whose degradation rate under ultraviolet (UV) irradiation is as low as 0.2%/year. In contrast to competitors, which use work-around solutions implemented at module level to mitigate UV-induced degradation (UVID), such as UV blockers or down-converting foils, SolarGuard will directly seek at developing UV-unsensitive HJT and TOPCon solar cells, hence rendering the need for UV protection at module level moot. SolarGuard’s PV modules will thus offer a substantial power gain of 1.5% at module level, owing to the removal of UV-blocking materials in the module bill-of-materials. This results in appreciable savings for PV manufacturers, namely 0.4$cts/W lower cost of goods sold (COGS) for a 5-GW PV production line. In addition, SolarGuard’s low degradation rates allow to considerably boost the energy yield of PV systems along their operational lifetime. Consequently, SolarGuard’s PV modules will enable a 30% (resp. 35%) lower levelized cost of electricity (LCoE) for a 10 kWp rooftop installation (resp. a 10 MW alpine PV plant) over 40 years of operational exploitation.To reach this ambitious goal, the original approach of SolarGuard is to proceed to extremely harsh UV irradiation, with acceleration factors up to 1,000x compared to AM1.5G solar spectrum, to quickly identify and down-select the most UV-resilient materials for HJT and TOPCon devices. Dedicated opto-electrical and microstructural analysis will be conducted to unveil the root causes of UVID and to support the development of UV-resilient materials. Regarding materials for HJT devices, the novelty brought by SolarGuard lies in the use of hydrogen doping for transparent conductive oxides (TCOs), enabling UV-resilience while relaxing the tradeoff between optical transparency and electrical conductivity. For TOPCon solar cells, compact, sputtered polySi layers as well as plasma oxides will be used to obtain UV resilience. Besides, an additional high risk/high reward approach, relevant to both HJT and TOPCon, will be investigated in SolarGuard, namely the development of alternative transparent conductive materials based on nitrides instead of oxides, especially gallium nitrides. With such transparent conductive nitrides (TCNs), SolarGuard aims at reaching a total unsensitivity to UV photons.Among renewables, PV is poised to be the key pillar to propel humanity toward a low carbon energy system. However, with the global PV market turning 2023 in an overcapacity situation, technological edges enabling performance boosts or cost advantages are eagerly sought for by PV manufacturers. With pilot series production expected in 2030, SolarGuard’s PV modules will provide both superior performance and reduced manufacturing and exploitation costs, and are therefore perfectly suited to tackle this challenging situation.

Photovoltaics (PV) plays the key role for the transition of our energy supply system to a sustainable low-CO2 economy. Especially due to transformation losses and high costs for storage, PV-generated electricity must be as economic and scalable as possible with the lowest use of resources and energy during fabrication. Perovskite solar cells as a promising young research field have the largest potential to meet those criteria. However, challenges in the stability and reproducibility hinder a fast commercialization. These issues are accompanied by a lack of control and understanding on how nanoscale features of the employed materials correlate with the performance metrics of solar cells.This research project aims for establishing a strong link between nano and device scale. The overall objective is to develop a characterization toolbox by scaling macroscopic optoelectronic characterizations to the micro and nano scale. Specific aims address the role of material inhomogeneities on the nanoscale such as grain boundaries and interfaces between layers. Physical parameters related to charge transport and recombination will be extracted. Furthermore, the first steps of degradation upon exposure to heat and light will be investigated.To achieve these goals, a nanoscale methodology will be developed based on a combined experimental and simulation approach. Experiments are performed using atomic force microscopy (AFM) including various modes such as conductive AFM and KPFM combined with colocalized confocal optical microscopy. These available techniques will be further developed to record local current-voltage, impedance, and transient optoelectronic signals. These data will be compared with a three-dimensional device simulation that is to be developed. The model contains the geometry of the tip and the nanostructure of the film, which allows to go much beyond simplified state-of-the-art analysis of e.g. diffusion measurements. A major innovation is that we will “break” the device, which consists of a stack of various layers, into two parts. One part remains on the substrate and the second one is the tip itself, which is coated with the layers of the other part of the device. We expect that this approach allows us to probe what is going on under operation in various layers and record data that has never been measured, e.g. nano-electroluminescence beyond the diffraction limit. Furthermore, cross sectional studies will be conducted to investigate various influences such as mobile ions and inhomogeneities by correlative microscopy in operando and as a function of the temperature. Advanced image analysis and comparison with tailored simulations will assist us with the quantification of parameters, which is commonly a challenge in imaging techniques.Both, the specific results on the perovskite solar cells as well as the developed methodology will impact research in PV and allow for a targeted tackling of weak points in the performance. The new methods will shape the progress in in-situ and in-operando studies in materials science in general, an emerging field with high demand.

To reach decarbonization goals of net-zero carbon emissions by 2050, an unprecedented increase in solar photovoltaic (PV) production and deployment is required in the forthcoming years. It is estimated that 63.4 TW of PV needs to be installed worldwide, a more than 60-fold increase from the currently installed 1 TW.Metal halide perovskite solar cells (PSC) are an emerging thin-film PV technology projected to play an important role in the terawatt-level PV deployment, either as a competitive alternative or tandem partner to the mature crystalline silicon (c-Si) technology. PSCs gained significant interest in recent years with remarkable and unprecedented power conversion efficiencies that have reached 26.1% for single-junction solar cell in only over a decade of research. Other advantages of PSCs include lower costs and simplicity of fabrication, adaptability to large-area processing, and compatibility with other PV technologies for tandem application. Efforts on fabricating tandem devices enabled by the tunability of PSC bandgap are gaining popularity due to promised reduction of $/W, with the EPFL PVlab standing at the forefront of this research. The current record efficiency of c-Si/PSC tandems is 33.9%, and several companies (e.g., Oxford PV, Hanwha Q Cells, etc.) are attempting to commercialize the technology.With this aim in mind, research focus is progressively shifting from pursuing PSC efficiencies to stability studies, as scalability, manufacturability and durability of the technology are lagging behind their laboratory-scale success. The lack of long-term operational stability in the outdoor environment is currently the major hurdle and technological barrier to commercialization. In this framework, the proposed project entitled ‘Failure analysis of PErovskite-based modules towArd long-term field ReliabiLity’ (PEARL) aims to address current challenges and bottlenecks in perovskite-based module reliability by applying lessons learnt from commercial c-Si PV technology and develop appropriate encapsulation and failure analysis strategies. Besides the susceptibility to moisture and oxygen that can be prevented by introducing adequate encapsulation techniques, some of the main degradation modes include thermal degradation, light-induced degradation, potential-induced degradation (PID), reverse-bias degradation from partial shading, mechanical delamination, and (electro)-chemical corrosion. Stressors such as light (including ultraviolet (UV)), temperature, and bias induce chemical reactions and/or elemental migrations through interfaces in cells and encapsulated modules, resulting in severe and irreversible power loss. Modifications in PSC device stack, compositional changes, and additive doping are explored as paths to enhance PSC stability. However, the multitude of possible device and module architectures, interfaces, and compositions are making our understanding of PSC reliability challenging.Proper encapsulation of perovskite devices is essential; however, typical PV encapsulation strategies involve the use of elevated temperatures, and polymeric materials producing volatile products and possibly reactions harmful to PSC during lamination or operation lifetime. Glass/glass with desiccated edge seal with or without a sheet of transparent polymeric encapsulant were proposed to encapsulate perovskites. However, as of now, there are only a few durability studies providing fundamental understanding of the degradation mechanisms in encapsulated perovskite-based cells or modules. To this end, efforts are made to design and standardize accelerating testing for perovskites, such as the International Summit on Organic Photovoltaic Stability (ISOS) protocols. Accelerated stress tests aim to reproduce field failure and the US-based Perovskite PV Accelerator for Commercializing Technology (PACT) plays an important role to bridge the gap between the outdoor and indoor performance by providing independent testing and validation of the fielded module performance and develop standardized testing protocols for perovskite modules.Scaling up from cell to module reveals additional weaknesses of the technology, including processing heterogeneities, vulnerabilities from connecting individual cells, and greater mechanical stresses at the interfaces. Introducing a polymeric encapsulant into the module may have two-fold consequences: a low-modulus encapsulant would provide mechanical support reducing risk of delamination; however, introduction of additional interfaces may cause elemental migrations and interactions-in particular between encapsulant additives and the cell stack. For example, PV encapsulants play an important role in power loss of c-Si modules, typically from action of UV and bias resulting in decomposition and interaction of UV absorbing additives and interfacial elemental migrations, respectively.Proper methodologies to characterize degradation on a module-level are yet to be developed. The challenges arise from sensitivity of the materials requiring delicate handling and an inert atmosphere. Strategies to deconstruct c-Si and thin-film CdTe and CIGS modules are in place, but these technologies are significantly more robust and environmentally stable.In the proposed work, I would like to address the above-described challenges to perovskite reliability with lessons learnt from c-Si PV. In the three operational work packages of the project (module fabrication, stress testing, and destructive analysis) I will (1) optimize perovskite module packaging with suitable materials and methods, transferable from single- to multi-junction module architectures, (2) monitor degradation rates during accelerated UV weathering and outdoor aging focusing on effects of module encapsulation, (3) develop destructive methodology to extract module areas of interest for characterization, and finally (4) elucidate degradation mechanisms through advanced material characterization.The unique aspect of this study relies in developing a damage-free module packaging and dismantling strategy adaptable to a variety of perovskite-based single- or multi-junction architectures. Because perovskite technology advances fast with module and layer composition and designs constantly changing and improving, the transferability of the approach to study degradation mechanisms is key. Among the few publications on perovskite module stability, there are hardly any focusing on understanding the failure on a module level, and none on analyzing a cross-section of a full module stack. Finally, UV weathering studies of perovskites have been largely neglected due to eliminating UV-sensitive layers such as TiO2, and SnO2 or possibility of using UV-blocking encapsulants. However, UV is one of the most severe stress factors affecting c-Si modules, causing photo-oxidative degradation of PV encapsulants. Addressing these steps is critical to advance perovskites a step closer to commercialization and may be also valuable for their application in different fields.

The project aims to comprehensively understand and enhance the adoption of residential photovoltaic (PV) systems within diverse socio-economic and environmental contexts. By analyzing factors influencing homeowners' decisions to adopt solar energy, this study identifies key motivators and barriers across different regions. Through a mixed-methods approach, incorporating both quantitative data analysis and qualitative interviews, the project seeks to unravel the complex interplay between economic incentives, regulatory frameworks, cultural attitudes, and environmental awareness. Recommendations will be tailored to policymakers, industry stakeholders, and community leaders to foster a supportive ecosystem for PV adoption. The ultimate goal is to contribute to the global transition towards sustainable energy, reducing carbon footprints, and promoting energy independence among residential sectors.

The negative impacts of climate change become increasingly visible. The major reason for climate change is our non-sustainable way of life, in particular regarding burning fossil fuels. Despite the dramatic situation, humankind seems not willing to drastically change their energy-demanding habits. Thus, a fast technological solution is the only way to mitigate the most severe consequences. Here, photovoltaics comes into play, which hardly causes CO2 emission during operation. However, the fabrication of conventional silicon modules releases CO2 and requires a lot of energy during refining the silicon and producing wafers. This drawback could be overcome by thin-film technologies, which require much less material and energy during manufacturing. Most promising are metal-halide perovskites here due to their excellent optoelectronic properties despite being processed from solution and with precursors of much lower purity than silicon.Power conversion efficiencies of perovskite solar cells reached more than 25% and, employed in tandems cells, even more than 30%. However, achieving high long-term stability remains challenging. Beyond external factors such as humidity, further culprits are mobile ions in the perovskite, phase-instabilities, and reactions with other materials in the device stack. All these properties are related to interfaces in the solar cells. In fact, for such a thin film (<0.5 µm) of a high-quality material as nowadays perovskites are, interfaces dominate the overall behaviour of the solar cell. Thus, a lot of effort has already been dedicated to interfaces. However, the conventional interface control has been mainly based on a trial-and-error approach without considering distinctive characteristics of various surface termination originating from organic and inorganic composites in halide perovskite crystals. More importantly, a lack of collective understanding regarding the electronic properties at heterojunction interfaces hinders perovskite solar cells (PSCs) from reaching the theoretical performance. Beyond the interface itself, the bottom layer additionally determines the bulk properties by influencing the perovskite growth. Thus, understanding and tailoring the functionality of interfaces is key for highly efficient and stable PSCs and thus subject of this research project.The goal is to achieve stable perovskite solar cells by a holistic strategy on tailoring and understanding both top and bottom interface. This approach requires a highly interdisciplinary team of chemists, materials scientists, and device physicists, which is provided by the Korean-Swiss consortium. In terms of materials, covered by the Korean side, we will go beyond the state of the art of conventional interface passivation strategies and work on surface reconstruction methods on the top interface to make the “interface region” more resilient during stress occurring under operation. For the bottom interface we will focus on strain control by heteroepitaxy since strain has been recently identified as a reason for enhanced recombination and reduced long-term stability due to undesired phase transitions. Evaluating the effect of such combined interface + close-by-regions engineering on the optoelectronic properties requires subtle and accurate optoelectronic characterization. Those will be undertaken by the Swiss partner, who will extend methods that are established for homogeneous bulk properties towards providing spatial resolution. We will achieve this goal by combining advanced photoluminescence and transient electrical measurements with numerical device modelling. They will be complemented by characterization on the nanoscale using colocalized optical and atomic force microscopy on cross sections of operational devices.Since the target of the project are highly stable solar cells, the operational stability will be assessed under various ambient conditions. Beyond tracking the stability, we will employ periodic electrical characterization in situ to understand the underlying degradation mechanism.The outcomes of this project will be highly relevant for the perovskite community and more generally for materials science. The developed methodology both experimental and theoretical, can be transferred to other problems in solid state physics. The more stable perovskite solar cells will contribute towards the fast development of a novel photovoltaic technology that can help us in fighting climate change.

Upgrading a silicon (Si) solar cell with a second solar cell made of a metal halide perovskite (Pk) is the most promising route to continue the learning curve of photovoltaic (PV) in the medium to long term. Pk materials can be deposited at low temperatures, involve elements that are available in sufficient quantities for mass production, and yield highly efficient solar cells in the lab, up to 25.7% on 0.1 cm2 in a single-junction, and up to 31.25% on 1 cm2 when combined with Si in a tandem. However, the technology will contribute to the energy transition only if these high performances can be replicated on industrially meaningful, scales (>>100 cm2) and if operational lifetimes can be extended to approach those of Si PV (>20 years). RADICALS aims to make key contributions on these points by demonstrating Pk/Si tandems yielding i) efficiencies of >30% on >100 cm2 and ii) long operational lifetime (indoors and outdoors). To do so, we will first build an in-depth understanding of the working principles and optimal growth conditions of the Pk and contact materials. More specifically, we will focus on self-assembled monolayer (SAM) contacts due to their excellent performance in lab-scale Pk cells. The investigation of this family of materials will also require the development of innovative modelling and characterization methods. Based on this understanding, we will then devise new classes of SAM materials to improve performance and stability, first of small-scale prototypes. We will then scale-up the deposition of the newly developed SAM and Pk materials, targeting high deposition throughput, robustness to defects, reproducibility, and high coating quality on M6 Si wafers. The small and large-scale PV devices will then be exposed to various operational stresses, both indoors and outdoors, to identify and mitigate degradation pathways. RADICALS combines the strengths of the groups of four applicants and two project partners. EPFL PV-LAB (main applicant), thanks to its expertise in highly efficient small-scale Pk/Si tandems and their characterization, will lead device integration tasks. KTU, who developed the SAM contacts used in the last two Pk/Si tandem records, will lead the development of the new contacts, supported by the partner CSEM NANO, who will focus on the characterization and optimization of SAM-treated surfaces. ZHAW and the partner FLUXIM have access to a large set of optical and electrical characterization methods coupled with multiscale modelling software, a knowledge that will be used here to understand performance-loss pathways across multiple length-scales. Finally, the co-applicant CSEM PMD will validate the project advances by demonstrating large-area Pk/Si tandems (>100 cm2) that reach the targeted performance and operational stability.

Perovskite solar cells (PSCs) have received vigorous attention from academia and industry due to their high efficiency (25.7%), solution processability, and low cost. Stacking two perovskite solar cells with complementary bandgaps in a monolithic tandem solar cell (TSC) configuration, highest certified efficiency of 26.4% has been achieved on glass substrates, surpassing other types of polycrystalline thin-film solar cells. However, all-perovskite monolithic tandems are still far from reaching their practical efficiency potential (>32%), and the long-term stability under operation conditions remains a grand challenge. Particularly, (a) wide-bandgap (WBG, 1.75-1.85 eV) mixed-halide perovskites usually suffer from high trap density (manifest as low PLQY) and severe photoinduced halide segregation that leads to large VOC-deficit (> 500 mV) and poor operational stability in solar cells; (b) narrow-bandgap (NBG, 1.2-1.3 eV) mixed Pb-Sn perovskites are prone to oxidation (from Sn2+ to Sn4+), which results in a high density of Sn vacancies that degrade the optoelectronic quality and stability of the films. Consequently, a short carrier diffusion length limits the thickness of NBG perovskite well below 1 ?m and results in incomplete near-infrared photon absorption and hence usually low JSC (~ 85% of Shockley-Queisser limit). To overcome the stability and efficiency limiting challenges, several key scientific challenges need to be addressed: 1) can we thermodynamically stabilize WBG perovskites with high PLQY? 2) is it possible to fundamentally eliminate the Sn oxidation pathway? 3) what are the microscopic fundamental degradation mechanisms in tandem solar cells? To this end, we aim to design and develop substrate configuration all-perovskite monolithic tandem solar cells on flexible and textured substrates that could deliver both extremely high operational stability and efficiency. The main idea is to develop novel materials, processes, photon and carrier management strategies, advanced cell architecture, and a fundamental and universal understanding of instability pathways and performance losses (and their interdependency). We will focus on: 1) developing radically different substrate configuration tandem architecture to eliminate metal-induced degradation pathway; 2) design and implementing rear surface texturing to improve the light trapping of near-infrared photons for significantly improving the JSC of NBG perovskite subcell to above 95% of the S-Q limit, without increasing the absorber thickness; 3) developing a new PVD/Blade-coating method that allows combinatorial materials synthesis to explore largely unexplored compositional and structural space of NBG (~ 1.2 eV) and WBG (~ 1.8 eV) perovskites to discover new chemically and structurally robust perovskite materials with simultaneous high optoelectronic quality and stability; this approach allows exploring new fabrication method to fundamentally eliminate Sn oxidation pathway, and novel concepts, such as high entropy alloying, to thermodynamically stabilize WBG perovskites; 4) developing advanced characterization workflow to gain comprehensive understanding of defects, structure, and optoelectronic properties as well as (thermal- and photo-) stability of new materials and associated interfaces that could guide materials and devices development; This will enables a fundamental understanding and establishment of a complex relationship between composition-optoelectronic property-stability, which is currently missing in the field. The project will progress in an iterative feedback loop consisting of device architecture design, new materials exploration, mechanism understanding, interfaces and solar cell optimization. Based on this approach, novel substrate configuration monolithic all-perovskite TSCs will be developed on flexible and textured substrates with both extremely high efficiency (~28%) and stability with T95>2000 hours stressed at MPP.

Among the emerging energy production technologies, metal halide perovskite solar cells (PSCs) have attracted extensive attention from both academia and industry as their power conversion efficiency (PCE) has increased from 3.8% to a certified 25.5% in a decade. This is even more remarkable considering that low cost solution processing technology is used. The main remaining challenge for the commercialization of PSCs lies in their limited lifetime due to a low stability of the material and devices. This is challenging because the understanding of the fundamental chemical reactions and electrical processes at the origin of the device degradation is complex and ageing tests are time consuming. Beyond irreversible degradation due to moisture, oxygen, and thermal stress, there are partially reversible processes, which increase the complexity of stability tests and pose challenges for characterization and simulation of the operational principle of devices in general and during aging. Despite remarkable progress in improving the stability, reported lifetimes are still far from what is expected from a PV technology. Therefore, a lot of research is necessary on the sources of degradation within solar cell devices under operation. To speed up this research, it is important to get a better understanding of the degradation pathways, from a fundamental point of view, and to find ways to accelerate ageing tests and obtain rapid feedback, which is the goal of this project.In more detail, we intend to address the following questions:-Which are the best stress factors for accelerated aging?-How can degradation be monitored by non-destructive in-situ measurements, also considering the peculiarities of perovskite solar cells such as slow reversible effects?-How can the observed changes be attributed to distinct physical parameters?-How can acceleration factors be identified from the degradation patterns and be used to predict lifetime under operation? Associated with these questions are the following research goals:-Design of tailored experiments for accelerated aging and identification of the most suitable stress factors and their parameter range-Development of suitable in-situ characterization based on opto-electronic measurements that allow distinguishing changes in charge transport and recombination-Application of numerical device simulation based on drift-diffusion models to identify the most likely origin of degradation during aging by quantifying changes of material parameters-Development of predictive models that based on the acceleration factors allow lifetime estimations for given operating scenarios and ambient conditionsTo answer these questions and achieve our goal we are going to combine degradation studies on a statistically relevant sample size with in-situ characterization and paired with device modeling to identify degradation patterns and their underlying physical cause. To fabricate the solar-cell samples, a combination of laser etching, inkjet-printing, screen printing, lamination and thermal evaporation will be used. Concerning the ageing study samples will be stress in environmental chambers that allow a fine control of parameters such as light intensity, humidity and temperature. To characterize the samples, a combination of structural (SEM, XRD) and optoelectronic measurements (impedance spectroscopy, electroluminescence, steady-state and transient photocurrent and photovoltage as a function of illumination intensity, etc.) will be used. The results will be analyzed using available device simulators. These tools allow to solve numerically the semiconductor equations (continuity, drift, diffusion, Poisson) for the whole solar-cell stack.We anticipate that the results of this project will allow us to improve the knowledge regarding degradation mechanisms of perovskite photovoltaic devices and lead to an establishment of fast, reliable and cost-effective stability measurement standards, which will be applicable by the whole research community. On the long run, these outcomes should facilitate a faster development of stable perovskite-based PV helping this technology to penetrate more easily the energy market. This would help to accelerate the decarbonization of the economy, thus reducing the disastrous impact of global warming on our society.