Halide perovskite solar cells have rapidly emerged as a leading candidate in next-generation photovoltaics due to their high efficiency and cost-effective fabrication. However, their commercial viability remains challenged by environmental and stability concerns. In this work, we present a comprehensive approach to the sustainable development of halide perovskite photovoltaics through environmentally conscious materials and processes. Key strategies include the use of green solvents for perovskite film deposition, enabling safer and more scalable fabrication routes. We demonstrate the fabrication of fully flexible perovskite solar cells under ambient air conditions using low-toxicity, eco-friendly solvents. To further minimize solvent use, we explore solvent-free thermal evaporation as an alternative method for perovskite layer deposition, significantly reducing chemical waste. Additionally, we replace conventional noble metal electrodes with carbon-based back contacts, offering a cost-effective and sustainable alternative with good conductivity and stability, showcasing potential for full roll-to-roll production. Finally, we address the critical issue of lead toxicity by partially substituting lead with tin in mixed Pb-Sn perovskite compositions, achieving reduced environmental impact while maintaining promising photovoltaic properties as single junction as well as in perovskite/perovkite tandem.

Together, these innovations mark significant progress toward greener, safer, and more sustainable perovskite solar technologies suitable for widespread deployment.

Among emerging photovoltaic technologies, perovskite solar cells stand out as particularly promising.[1] They offer unique advantages, including semitransparency, mechanical flexibility, and a tunable band gap,[2-4] making them especially attractive for tandem architectures, agrivoltaics, and building-integrated applications.

One of the key challenges, however, is the intrinsic instability of perovskite materials when exposed to moisture. For this reason, high-quality perovskite films are typically fabricated in controlled, nitrogen-filled gloveboxes. [5] While effective, this approach increases fabrication complexity and cost, ultimately limiting scalability.

Moving toward ambient-air processing would therefore represent a major step forward, enabling simpler and more cost-effective manufacturing. However, due to the sensitivity of perovskites to water and oxygen, significant changes in film formation and device performance are generally expected under these conditions.

In this talk, I will present our recent results on the deposition of perovskite films in ambient air using different material formulations, solvent systems, and additives. [6-8] Interestingly, for selected compositions, the optoelectronic quality of the films is not only preserved but even enhanced when processed in ambient air, resulting in reduced defect density and improved film morphology.

In particular, formamidinium lead iodide (FAPbI₃) perovskite deposited in ambient air shows an increase of over 40% in average visible transmittance compared to samples fabricated in a nitrogen-filled glovebox, while still achieving a power conversion efficiency of 13.8%, an average visible transmittance of 30.4%, and a light utilization efficiency of 4.2%.[9]

These results not only demonstrate a record LUE for this class of devices, but also highlight the potential of ambient-air processing as a viable route toward the large-scale fabrication of semitransparent perovskite solar cells.

Perovskite photovoltaics combine high power-conversion efficiencies with low weight, mechanical flexibility, and bandgap tunability, making them highly attractive for both terrestrial energy generation and next-generation space power systems. However, their practical deployment is still limited by stability losses that depend strongly on the operating environment. In this contribution, we identify the dominant degradation pathways in perovskite-based single-junction and tandem solar cells and discuss how these mechanisms evolve from standard Earth-based operation to the extreme conditions relevant for space applications.

Therefore, we focus on ion-related instabilities as a central origin of performance losses. In particular, we show how mobile ions can induce operational degradation and current losses, even in highly efficient passivated devices, where interfacial treatments improve open-circuit voltage and fill factor but can also introduce new instability pathways under working conditions. Our recent works further show that even minor halide segregation is closely coupled to ionic loss processes and strongly affects the evolution of device performance over time, making it one of the main factors limiting the energy–lifetime product of perovskite tandems.

We extend this analysis toward space photovoltaics, motivated by our satellite demonstration efforts. Space deployment exposes devices to extreme environments, including low temperatures, low-intensity illumination, and repeated temperature cycling during orbital operation. Under such conditions, all-perovskite tandems can experience severe performance constraints, especially in the wide-bandgap top cell, where low-temperature operation can enhance demixing, intensify ion-related losses, and induce subcell current mismatch. These effects are particularly critical in monolithic tandems, where degradation in one subcell directly compromises the performance of the full device stack. On the other hand, ionic mobility enables self-healing and repair mechanisms, resulting in high resilience to high-energy proton irradiation. Lastly, I would like to highlight the relevance of mechanical reliability, especially for lightweight and flexible perovskite devices. Flexible architectures are highly promising for both portable terrestrial applications and space platforms because of their low mass and conformability. At the same time, bending, handling, launch-associated stress, and repeated deformation can generate mechanical damage such as microcracks, interfacial delamination, or electrode failure, strongly degrading performance.

Overall, I will provide an overview of the stability-limiting mechanisms in perovskite single-junction and tandem photovoltaics for Earth and space applications, which we are currently investigating. Beyond advanced understanding, linking halide segregation, mobile-ion dynamics, low-temperature and thermal-cycling effects, and mechanical damage in flexible devices, I will show mitigation strategies that significantly stabilize performance for the investigated stressors.

Halide perovskite solar cells (HPSCs) hold strong potential for next-generation photovoltaics in space applications owing to their high specific power and proton radiation tolerance. Yet, achieving long-term stability under operational stressors such as heat, prolonged illumination, and ionizing radiation remains a key challenge, particularly for applications in space and other harsh environments. Here, we report a dual-passivation approach that incorporates cerium oxide (CeOx) nanoparticles into the perovskite absorber layer using an n-octylammonium iodide (OAI)-assisted post-treatment. CeOx, a redox-active oxide widely used in radiation shielding, improves crystallinity, reduces defect density, and enhances interfacial energy alignment. The resulting devices exhibit a power conversion efficiency (PCE) of 24.9%, the highest reported for n-i-p HPSCs employing poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) as the hole transport layer. Under 0.05 MeV proton irradiation at fluences up to 2 × 10^14 protons cm^-2, the treated devices retained 91% of their open-circuit voltage and 81% of their initial PCE. Spectroscopic and electrical analyses revealed suppressed non-radiative recombination, preserved grain boundary potential, and improved photothermal stability. These results demonstrate that CeOx incorporation offers an effective strategy for enhancing the durability of perovskite solar cells under simultaneous environmental and radiation exposure, paving the way toward reliable deployment in both terrestrial and aerospace energy technologies [1].

Small phosphonic acid molecules, so-called self-assembled monolayers (SAMs) have become standard materials in p-i-n perovskite solar cells (PSC) [1]. However, the relationship between molecular structure and device performance remains unclear, despite the wide variety of these molecules. Previous studies have shown that changes in chromophore, linker, anchoring or functional groups can influence device performance [2, 3]. Nevertheless, systematic comparison remains challenging, due to differences in perovskite composition, device architectures across studies as well as limited molecular datasets per study.

Here, study provides a comparison of a larger set of nine phosphonic-acid molecules, evaluating the device performance within the same PSC structure [4]. This work aims to understand how different substitution patterns on the carbazole core influence the properties of the layer and the performance of photovoltaic devices. A series of differently substituted carbazole derivatives with phenyl-, methyl- and methoxy- functional groups was synthesized and integrated into devices.

The compounds substituted at the 3,6-positions showed improved fill factors and power conversion efficiencies relative to other configurations. A correlation between ionization potential and fill factor also points to a threshold value, beyond which performance declines, likely due to energy level misalignment. Overall, this study highlights that subtle changes in molecular design can lead to significant differences in interfacial energetics behavior and provides guidance for future work on phosphonic-acid-based materials for high-performance PSCs.

Research on Hybrid Halide Perovskite (HHP) has reshaped photovoltaic research in the last decade and has recently approached the commercial scale in tandem configuration. While a wide range of material’s band gaps have been explored to adapt to the different applications, single-junction devices require a band gap of approximately 1.5 eV, indicating formamidinium lead triiodide (FAPbI₃) as the ideal solution. However, the main challenge when working with FA-based perovskites is the high temperature (~160°C) required for the phase transition to occur from the optically inactive non-perovskite δ-phase to the optically active cubic α-phase. Preventing the photoactive phase from degradation - especially at low processing temperatures (<150°C) - remains therefore a key challenge. Conventional strategies to stabilize the cubic FAPbI₃ phase rely on MA-assisted formulation; on one hand, this strategy successfully reduces the annealing temperature of the perovskite active layer to around 100 °C, but on the other hand the inclusion of smaller cations inevitably widens the band gap and introduces phase segregation.

In this context, we present a new strategy to stabilize the cubic α-phase of FAPbI₃ without the addition of MA-based additives and at low processing temperatures. We employ 2% of Cs inside the precursor solution and a binary solvent system with balanced polarity by introducing a polar alcoholic component in the anti-solvent system. This combination enables the phase conversion from δ- to α-FAPbI₃ at just 100 °C temperature, thus stabilizing the photoactive phase. Interestingly, when comparing FAPbI₃ processed using this method with FAPbI₃ prepared using conventional MACl additives, we observe a reduced band gap (1.53 eV) and larger lattice parameters. To demonstrate the effectiveness of our strategy, we fabricated solar cell devices in an inverted (p–i–n) configuration using FAPbI₃ films processed with both a binary solvent system and single solvents. While the devices prepared using single solvents exhibited low PCE, mainly due to the incomplete conversion of the active layer, the ones fabricated with the binary solvent system achieved PCE approaching 22%, thus opening a new path for low temperature processed FA-based solar cells.

The transition from lab–scale breakthroughs to industrial-scale production of perovskite–based tandem photovoltaics demands robust, scalable fabrication strategies. While tandem architectures promise record–breaking efficiencies, their commercial viability hinges on durability as well as fabrication process reliability, uniformity across large areas, and integration into existing manufacturing ecosystems. Solution–based processes dominate at the laboratory scale, benefiting from fast optimization feedback and straightforward integration in modern research environments. Scalable solution-based techniques such as slot-die coating and inkjet printing are widely investigated for their potential in large-area, high–throughput deposition. However, for industrial thin–film manufacturing, vapor-phase deposition processes remain the standard due to their proven reliability and scalability.

This contribution discusses recent innovations in scalable fabrication methods, including slot–die coating, inkjet printing, vapor phase deposition, and digital process monitoring. Recent advances from KIT will be presented that address key challenges in upscaling perovskite tandem solar cells. In the area of printing and coating, we developed a hybrid two-step inkjet printing process that enables precise edge isolation and high–quality perovskite absorber layers for perovskite/silicon tandem devices (Pesch et al.). This method combines material efficiency with spatial control, supporting scalable tandem integration. Additionally, we introduced a spatially regulated gas-flow drying technique for large-area slot die coated films (Geistert et al.), which allows controlled solvent evaporation across the substrate, resulting in improved film uniformity and reproducibility–critical for large-scale manufacturing.

For vapor-phase deposition, we proposed strategies to overcome industrialization bottlenecks. Petry et al. developed a framework for evaluating the throughput of vapor deposition routes, including the arrangement and combination of linear sublimation sources and analysis of precursor thermal stability, aimed at enabling continuous and scalable processing. Diercks et al. present close-space sublimation (CSS) as a vacuum-based, industrially relevant deposition method for the conversion of sublimed PbI2 inorganic scaffolds into high-quality wide-bandgap perovskite absorbers. The latter work was pursues in close collaboration with teh University Valencia. 

Complementing these fabrication efforts, our work on in-situ monitoring and deep learning (Laufer et al.) introduces a predictive process control system that uses sensor data and neural networks to assess film quality in real time. This approach significantly enhances process reliability and yield, offering a pathway toward intelligent manufacturing.

References

Pesch, R. et al. Efficient Perovskite/Silicon Tandem Solar Cells Using Hybrid Two–Step Inkjet Printing with Edge Isolation Precision. Small Sci. 2025, e202500362. https://doi.org/10.1002/smsc.202500362

Geistert, K. et al. Spatially Regulated Gas Flow Control for Batch–Drying of Large Area Slot DieC oated Perovskite Thin Films. Adv. Energy Mater. 2025, 2500923. https://doi.org/10.1002/aenm.202500923

Petry, J. et al. Industrialization of Perovskite Solar Cell Fabrication: Strategies to Achieve High Throughput Vapor Deposition Processes. EES Sol. 2025, 1, 404–418. https://doi.org/10.1039/D5EL00069F

Diercks, A. et al. Close Space Sublimation as A Versatile Deposition Process for Efficient Perovskite Silicon Tandem Solar Cells. A- accepted for publication.

Laufer, F., Götz, M., Paetzold, U. W. Deep Learning for Augmented Process Monitoring of Scalable Perovskite Thin–Film Fabrication. Energy Environ. Sci. 2025, 18, 1767–1782. https://doi.org/10.1039/D4EE03445
 

A major challenge for the practical application of perovskite solar cells (PSCs) is their limited operational stability. In n–i–p device architectures, all state-of-the-art PSCs with high power conversion efficiencies (PCEs) currently rely on the benchmark hole transport layer (HTL) Spiro-OMeTAD, which is conventionally doped with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 4-tert-butylpyridine (tBP). However, these dopants substantially compromise device stability. Furthermore, the complex in situ oxidation processes associated with conventional Spiro-OMeTAD doping obscure the underlying mechanisms, thereby hindering the rational design of stable, high-efficiency HTLs.

Here, we introduce a clean, post-oxidation-free doping strategy for Spiro-OMeTAD based on stable organic radicals as dopants and ionic salts as dopant modulators, termed ion-modulated (IM) radical doping. In this approach, the organic radicals directly generate hole polarons, resulting in an immediate enhancement of conductivity and work function, while the ionic salts further tune the work function by modulating the energetics of the hole polarons. Previously, PSCs employing IM radical-doped Spiro-OMeTAD achieved high PCEs with excellent stability, exhibiting T80 lifetimes of approximately 1200 h under 70 ± 5% relative humidity and 800 h at 70 ± 3 °C without encapsulation, effectively mitigating the trade-off between efficiency and stability. By further optimizing the dopant system, we demonstrate a significant enhancement in the thermal stability of the Spiro-OMeTAD layer, which remains stable at temperatures up to 85 °C. Moreover, the resulting HTL effectively suppresses Au migration into the perovskite layer, further improving device stability.

Perovskite solar cells (PSCs) have rapidly emerged in the photovoltaic field, achieving remarkable increases in power conversion efficiency over the past decade [1]. These advancements have positioned PSCs at the forefront of next-generation solar energy research. However, despite their impressive performance, critical challenges remain for large-scale commercialization, particularly in terms of long-term operational stability and scalable, cost-effective manufacturing processes [2].

In this work, we explore the fabrication of  inverted PSCs on unconventional and lightweight substrates as a pathway toward novel applications and improved material utilization [3]. Specifically, we demonstrate the successful integration of perovskite devices on paper substrates through parylene modification, achieving the highest efficiencies reported to date for this approach. This method highlights the potential for low-cost, widely accessible, and sustainable photovoltaic solutions. In addition, we fabricate PSCs on parylene substrates to realize ultralight, flexible, and bifacial solar cells. These devices combine mechanical robustness with high performance, enabling new possibilities for portable, wearable, and aerospace energy systems. Lastly, we employ parylene as an encapsulation material to extend the operational lifetime of perovskite solar cells.

Briefly, the fabrication steps are as follows: transparent electrodes are deposited using an RF sputtering system, while NiOx and self-assembled molecules are employed for hole extraction. The perovskite absorber layers and electron transport layers (ETLs) are deposited via spin-coating. Additionally, buffer layers are optimized depending on the device architecture. The surface morphology of the substrates, as well as the growth of the functional layers, is characterized in detail. The resulting perovskite films exhibit high quality and crystallinity, even when processed on paper substrates.

Our results underline the versatility of perovskite materials and provide further insight into substrate engineering as a viable strategy for advancing both the functionality and commercialization potential of perovskite solar technologies.

The growing demand for sustainable energy solutions in urban environments has driven the development of building-integrated photovoltaics (BIPV), an approach in which solar modules are incorporated directly into architectural elements such as roofs, facades, windows, and railings. By bringing photovoltaic (PV) generation closer to demand centers, BIPV offers a compelling strategy to reduce costs and maximize solar energy utilization within the built environment. Among the various BIPV-enabling technologies, semi-transparent solar cells are particularly attractive because they allow partial light transmission while generating electricity, making them ideally suited for integration into buildings. Wide-bandgap (WBG) perovskites (E_ɡ > 1.7 eV) are commonly employed in semi-transparent architectures to balance transmittance and absorption; however, these bromide-rich compositions often suffer from halide segregation, photo-instability, and reduced long-term operational stability under continuous illumination. In this work, we introduce an alternative strategy based on thickness engineering of formamidinium lead iodide (FAPbI₃), a narrow-bandgap perovskite typically used in opaque device architectures. By precisely tuning the absorber thickness, we achieve high optical transparency and competitive power conversion efficiency, circumventing the intrinsic limitations of wide-bandgap perovskites and the limited performance of quasi-2D systems. Optical modeling reveals that thinning the FAPbI₃ layer effectively balances visible transmittance and device performance: absorbers of 140 nm and 160 nm deliver average visible transmittances (AVTs) of 24.2% and 18.2% alongside power conversion efficiencies (PCEs) of 15.9% and 18.0%, respectively. Surface passivation with 4-fluorophenylethylammonium iodide enhances the open-circuit voltage (V_OC) by over 100 mV and raises efficiency by more than 1%, as confirmed by photoluminescence and transient optoelectronic analyses showing reduced non-radiative recombination losses and extended carrier lifetimes. Crucially, both passivated and unpassivated devices exhibit excellent operational stability despite the reduced absorber thickness. These results establish thin FAPbI₃ as a robust and versatile platform for efficient, stable semi-transparent solar cells targeting BIPV applications.

Perovskite solar cells have reached high power-conversion efficiencies, yet their instability under operating and storage conditions remains a major obstacle to deployment [1,2]. In particular, device evolution is often non-monotonic, and recovery effects can complicate the interpretation of ageing experiments. Understanding how electrical performance changes under dark and light conditions relate to underlying physical processes is therefore essential.

In this work, we combine repeated current-voltage characterization with physics-based device simulation to investigate the evolution of perovskite solar cells during light and dark aging. A one-dimensional optoelectronic model is used together with a genetic-algorithm-based fitting strategy, allowing us to identify families of parameter sets consistent with the experimental device response rather than relying on a single fitted solution. This provides a broader basis for interpreting which parameter trends are robustly supported by the data.

Our preliminary results reveal reproducible non-monotonic behaviour across cells, with distinct evolution regimes observed during degradation and subsequent dark storage. The degraded state is most consistently associated with changes affecting charge-transport-related terms, while post-stress dark storage remains dynamic and can lead to partial recovery of photovoltaic performance. These observations highlight that perovskite solar cell behaviour cannot be understood from illuminated operation alone, and that dark evolution must also be considered when analysing stability.

Overall, this coupled experimental-modelling approach provides a practical framework for comparing device evolution under different conditions and for identifying the parameter trends that are most relevant to ageing and recovery in perovskite solar cells.

Hybrid Sn–Pb perovskite solar cells are promising candidates for tandem photovoltaic applications; however, their performance is frequently limited by severe photovoltage loss and insufficient operational stability, which mainly originate from interfacial recombination and poorly controlled crystallization processes. In this talk, I will present our systematic strategies to regulate interfacial recombination, crystallization dynamics, and carrier-selective contact properties through targeted interface engineering, growth modulation, and hole-transport-layer-free design. Specifically, dedoping PEDOT:PSS effectively reduces interfacial energy mismatch and suppresses non-radiative recombination, enabling more efficient hole extraction and a marked enhancement in open-circuit voltage.[1] Further modification using cPTANMe as a tailored hole transport layer improves interfacial energetics and charge selectivity, thereby minimizing recombination losses at the perovskite/HTL interface.[2] In parallel, a fullerene derivative is introduced as an additive to modulate crystallization behavior, refine film morphology, and stabilize the perovskite lattice, which mitigates interfacial degradation and enhances device durability. Beyond conventional HTL-based architectures, I will also discuss our recent progress in HTL-free hybrid Sn–Pb perovskite solar cells, where careful control of buried-interface quality, crystallization pathways, and interfacial energetics enables efficient charge extraction even in the absence of a dedicated hole transport layer. These HTL-free devices provide a simplified platform to uncover the intrinsic interplay between ionic distribution, interfacial defects, and non-radiative recombination, while also offering a practical route toward reducing parasitic losses and fabrication complexity.

Understanding the degradation mechanisms of perovskite solar cells (PSCs) remains a critical challenge limiting their large-scale deployment despite their outstanding power conversion efficiencies. This talk will cover a comprehensive investigation of PSC degradation pathways by combining in-situ X-ray diffraction (XRD) and impedance spectroscopy (IS), enabling simultaneous structural and electronic characterization under realistic operating conditions.

In-situ XRD reveals the dynamic evolution of the perovskite lattice during device operation, highlighting phase instability, strain accumulation, and the formation of degradation products. These structural changes are strongly influenced by external stressors such as light, electrical bias, and environmental exposure, which are known to accelerate ion migration and defect redistribution within the perovskite layer. Complementarily, impedance spectroscopy provides insight into the evolution of charge transport and recombination processes, capturing changes in capacitance, resistance, and ionic contributions that are directly linked to device performance losses.

By correlating structural and electrical signatures, we identify a multi-step degradation process governed by the interplay between ionic migration, interfacial reactions, and bulk defect formation. The results reveal that early-stage degradation is dominated by reversible ionic redistribution, while prolonged operation leads to irreversible structural decomposition and increased non-radiative recombination. Importantly, discrepancies between structural stability and operational stability are observed, underscoring the critical role of interfaces and mobile ions in determining device lifetime.

This combined operando approach provides a unified framework to disentangle the complex coupling between structural and electronic degradation pathways in PSCs. Overall, this work demonstrates the power of in-situ characterization to advance the understanding of degradation phenomena in next-generation photovoltaic technologies.

Circularly polarized luminescence (CPL) from semiconductor nanomaterials has emerged as a promising phenomenon for next-generation photonic technologies, including advanced displays, optical data transmission, and chiral sensing. Among the various emissive nanomaterials, perovskite nanocrystals (PNCs) are particularly attractive due to their exceptional optoelectronic properties. They exhibit high photoluminescence quantum yields, narrow emission bands, and facile spectral tunability across the entire visible range. Despite these advantages, achieving strong CPL from PNC-based systems remains challenging. In most reported approaches, the dissymmetry factor of luminescence is relatively low. Therefore, developing strategies that enable efficient CPL generation across the full visible spectrum remains an important goal.

In this work, we address these challenges by exploiting interactions between achiral PNCs and chiral organic templates [1]. Our approach relies on introducing nanocrystals into a chiral liquid-crystalline environment that provides a hierarchical supramolecular structure capable of transferring chirality to the emissive nanomaterial. To demonstrate the generality of this concept, we investigated three types of PNCs emitting in the red, green, and blue spectral regions. The nanocrystals were incorporated into a chiral liquid-crystalline matrix to form composite thin films, enabling controlled organization of the particles within the chiral host.

Structural characterization using electron microscopy revealed that the nanocrystals are not randomly dispersed within the matrix but instead assemble within nanoscale gaps created by the self-organized liquid-crystalline structure. These confined regions serve as templating sites that promote spatial ordering of the PNCs and enhance their interaction with the surrounding chiral environment. As a result, the composite films exhibit pronounced circularly polarized luminescence. Measurements of CPL show dissymmetry factors reaching values of approximately 0.24, which represents a suprisingly high level of circular polarization for perovskite-based emissive systems.

Analysis of the optical response indicates that the observed CPL originates from the interplay of two distinct mechanisms. The first mechanism is the intrinsic chiral organization of PNCs within the chiral liquid-crystalline template, which induces asymmetry in the emission process. The second mechanism arises from selective optical filtering by the chiral matrix itself, which preferentially transmits one circular polarization component over the other. Importantly, these two effects can coexist and reinforce each other, leading to a significant amplification of the CPL signal.

A key advantage of the presented system is the possibility of tuning the relative contribution of these mechanisms. By selecting nanocrystals emitting in different spectral regions and controlling the mode of their assembly within the liquid-crystalline matrix, it is possible to adjust the spectral overlap between the emission band and the optical activity of the host structure. This enables control over whether intrinsic chiral emission or selective filtering dominates the resulting CPL response.

Overall, this study demonstrates a versatile strategy for generating highly dissymmetric circularly polarized luminescence from achiral perovskite nanocrystals embedded in chiral liquid-crystalline templates. The resulting thin film composites combine strong polarization selectivity with spectral tunability across the visible range, offering a promising platform for the development of CPL-based photonic materials and devices.

In recent years, chiral materials have garnered significant attention due to their promising applications in optoelectronics, chemical sensing as well as quantum computing [1-3]. The chiral characteristics of both soft materials and inorganic systems offer valuable insights for enhancing their functional integration. Notably, hybrid materials have emerged as a rapidly growing area in materials science, especially in optoelectronics, as they allow fine-tuning of the properties inherent to both soft and inorganic components. Among these, chiral hybrid perovskites have stood out as a particularly compelling class, exhibiting strong circularly polarized emission without the need for costly ferromagnetic materials or extremely low temperatures. Additionally, they demonstrate intriguing chirality-induced spin selectivity (CISS) effects [4]. The chiral source influences specific non-covalent interactions within the scaffold, which in turn modulate the efficiency and expression of chiral properties [5]. Owing to advances in multiscale modeling and simulation, it is now possible to design chiral systems with unprecedented accuracy. In this talk, I will present recent contributions in predicting chiral behavior in chiral hybrid perovskites [6-8] also at high pressure conditions. I will introduce novel chiral design strategies that integrate enhanced sampling simulations with time-dependent density functional theory (TD-DFT) calculations derived from computed free-energy landscapes. This approach accounts for various contributions, such as molecular rotations within the chiral framework that can critically impact the emergence and optimization of chiral properties.

References

[1] Crassous, J.; Fuchter, M.J.; Freedman, D. E.; Kotov N. A.; Moon, J.; Beard, M.C. Nat. Rev. Mat., 2023, 8, 365-371.

[2] Albano, G; Pescitelli, G.; Di Bari, L. Chem. Rev., 2020, 120, 10145-10243.

[3] Jiang, S.; Kotov, N. A. Adv. Mater. 2023, 35, 2108431.

[4] Lu, H.; Xiao, C.; Song, R.; Li, T.; Maughan, A. E.; Levin, A.; Brunecky, R.; Berry, J. J.; Mitzi, D. B. ; Blum, M. C. Beard, J. Am. Chem. Soc., 2020, 142, 13030-13040.

[5] Pietropaolo, A. ; Mattoni, A. ; Pica, G.; Fortino, M.; Schifino, G.; Grancini, G.Chem, 2022, 8, 1231-1253.

[6] Fortino, M.; Mattoni, A.; Pietropaolo, A.; J. Mater. Chem. C, 2023, 11, 9135-9143.

[7] Fortino, M.; Schifino, G.; Salvalaglio, M.; Pietropaolo, A. Nanoscale, 2025, 17, 5823.

[8] Fortino,M.; Mattoni, A.; Feldmann, S.; Pietropaolo, A. J. Phys. Chem. Lett. 2025, 16, 10234-10239.

Since the first demonstration of efficient halide perovskite solar cells, there has been sustained and growing research interest in this class of materials. With facile deposition processes and excellent optoelectronic properties, these materials have found applications not only in photovoltaics, but in a myriad of optoelectronic devices. While research into halide perovskites for light emission and X-ray detection is just beginning to surge, perovskites are most well known for their remarkable PV performance, achieving certified power conversion efficiencies of 27%. Despite their truly impressive device performance, the stability of these materials is still a major obstacle to their widespread deployment. One of the potential reasons for this is a lack of understanding of how these materials crystallise, and ultimately, whether or how this impacts how they degrade under atmospheric/operational stressors. From controlling nanoscale mixing to devising new kinetic pathways to circumvent thermodynamic instabilities; in this talk, I will present a variety of methods to improve the stability of halide perovskite materials and devices.

Altering the optoelectronic properties of the widely used hole transport layer (HTL), namely, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), commonly known as PEDOT:PSS, with sodium polystyrenesulfonate (Na-PSS) overcomes limitations of the conventional pristine PEDOT:PSS HTL-based optoelectronic devices. The introduction of Na-PSS into pristine PEDOT:PSS results in a reduced energy barrier between the HTL and light-emission layer (EML), leading to improved hole injection, thereby lowering the turn-on voltage and improving the perovskite light-emitting diode (Pe-LED) efficiency. The pH value of acidic pristine PEDOT:PSS is modulated by the addition of Na-PSS, which aids in preventing the corrosion of the underlying semitransparent indium-doped tin oxide (ITO) electrode. The modulation of the pH value resulted in higher thermal tolerance of the perovskite emission layer coated on top of the HTL. The introduction of Na-PSS creates a PSS-rich environment, which prevents nonradiative recombination of excitons at the HTL/EML interface. This enhances the efficiency of the Pe-LED device by allowing more excitons to recombine radiatively. Moreover, the addition of Na-PSS modulates the conductivity of pristine PEDOT:PSS, resulting in effective confinement of charge carriers within the EML, increasing the probability of electron–hole recombination within the EML, and improving the device efficiency. The use of Na-PSS-modified PEDOT:PSS significantly enhances the performance of the Pe-LED device, and the efficiency values outperformed those of pristine PEDOT:PSS-based Pe-LED devices. The Pe-LED devices with Na-PSS-modified HTL have a low turn-on voltage (2.8 V)@1 cd/m², high external quantum efficiency (EQE) of 10.05%, and current and power efficiency of 40.89 cd/A and 35.95 lm/W, respectively. Most notable advantage of the Na-PSS-modified HTL is the significant improvement in the operational stability of the Pe-LED devices, with the electroluminescent (EL) lifetime 4 times longer in comparison to that of Pe-LED devices having pristine PEDOT:PSS as HTL.

Single and few-photon sources play a crucial role in various quantum applications, including quantum communication, quantum imaging, and are of great importance in quantum correlations. Semiconductor nanorods (NRs) offer a linearly polarized light emission, indicating the existence of dipole moments along with the long axis of NRs.
In this work, we wish to explore the emission anisotropy of CsPbBr3 NRs (aspect ratio~7.4) having photoluminescence quantum yields of ~84% using a newly developed approach that combines defocused imaging with heralded spectroscopy of single NRs. For this, we have used an innovative single photon avalanche diode (SPAD) array onto which the out-of-focus dipole emission pattern can be imaged, and resolved in time and space, allowing the direct observation and quantification of the difference between the emission transition dipole of the exciton (X) and biexciton states (BX) revealing multi-excitonic interactions in single perovskite NRs.1 Notably, g2(0) (~0.88 ±0.03), and lifetime for BX and X state (BX≈ 2.74 ± 0.23 ns; EX≈11.31 ± 1.11 ns) for single CPB NR shows that BX is very weakly bound, which is more in line with the observed similarity of X and BX anisotropy.
Following this advancement in quantum materials and techniques, we extend our study to quantum sensing considering nanodiamonds (NDs).2 Due to excellent biocompatibility, room temperature stable emission, nearly infinite photostability, nitrogen vacancy (NV-) centre in NDs has emerged as quantum sensor exploiting their magneto-optical response. Such approach provides scalable pathways toward quantum photonic devices and nanoscale quantum sensors for monitoring chemical and biological processes.
References:
(1) Amgar, D.; Lubin, G.; Yang, G.; Rabouw, F. T.; Oron, D., Nano Lett. 2023, 23 (12), 5417–5423.
(2) Barton, J.; Gulka, M.; Tarabek, J.; Mindarava, Y.; Wang, Z.; Schimer, J.; Raabova, H.; Bednar, J.; Plenio, M. B.; Jelezko, F.; Nesladek, M.; Cigler, P., ACS Nano 2020, 14 (10), 12938–12950.

Addressing the synergistic nonradiative losses in CsPbBr₃ perovskite quantum dots (PQDs)/polymer composites arising from interfacial defects and lattice softness is crucial for enhancing the photoluminescent (PL) performance. This study proposes a molecular interface engineering strategy employing the crosslinkable ligand 2-carboxyethyl acrylate (CEA). By constructing coordination-covalent bonds and covalent interfaces between CEA-modified CsPbBr₃ PQDs and a polymer matrix formed via the co-polymerization of CEA and pentaerythritol tetraacrylate PETA monomer, the resulting composites achieve a photoluminescence quantum yield (PLQY) of 78% and enhanced thermal stability, retaining ~ 41% of their initial emission intensity at 393 K after continuous heating. Femtosecond transient absorption and variable-temperature photoluminescence spectra reveal that the covalent interfaces not only passivate surface defects and suppress non-radiative recombination, but also effectively reduce exciton-phonon coupling and multi-phonon relaxation processes by enhancing lattice rigidity and increasing optical phonon energy.

Perovskite–silicon tandems have reached an exciting inflection point, moving from record-e:iciency 1 cm2 laboratory cells to truly manufacturable devices on full-size industrial G12 wafers, opening a compelling pathway beyond the long-standing limits of single-junction silicon photovoltaics. In this talk, I will share our latest progress in bridging the gap between lab breakthroughs and industrial-scale production, focusing on the practical challenges that emerge during upscaling and the solutions we found to overcome them.

Key topics include wide-bandgap perovskite compositional engineering to unlock higher voltage and improved stability, achieving high-quality perovskite growth on textured silicon surfaces, and developing scalable deposition routes that span both solution-processing and vacuum deposition. I will also discuss how we address reliability under thermal and operational stress, an essential requirement for real-world deployment.

Building on these advances, we achieved a certified 32.2% power conversion efficiency on a G12 silicon wafer, the largest wafer format widely adopted in the PV industry today. We further demonstrated module-scale translation by fabricating a 1.52 m2 module based on the 32.2% G12H wafer, delivering a Pmpp output of 414 W, setting a new performance benchmark for perovskite-based modules. Encouragingly, these modules have also shown strong operational stability, maintaining performance over several months of field testing.

Overall, this presentation highlights our roadmap and confidence in translating perovskite–silicon tandems from outstanding lab results into high-yield, large-area manufacturing readiness, accelerating their path toward commercial adoption.

Solution-processable semiconductors such as halide perovskites and certain molecules are promising for next-generation spin-optoelectronic applications [1]. Yet, we don’t fully understand what mechanisms govern charge, spin and light polarization in such emerging energy materials, and even less how these are affected by chirality [2]. In this talk, I will give an overview of our recent efforts to understand the spin-optoelectronic performance of these materials through time-, space- and polarization-resolved spectroscopy and microscopy, and how these insights may enhance the performance of solar cells and other energy conversion applications.

For investigating halide perovskite films, we pushed broadband circular dichroism to diffraction-limited spatial and 15 fs time resolution for creating a spin cinematography technique to witness the ultrafast formation of spin domains due to local symmetry breaking and spin-momentum locking [3]. I will then briefly explain the fundamentals and artefacts involved in measuring circularly polarized luminescence reliably and introduce an open-access methodology and code to do so [4]. Finally, I will show our most recent development of a transient sensitive broadband full Stokes-vector spectroscopy with unprecedented time- and polarization resolution to track the emergence of chiral light emission [5].

[1] Nature Reviews Materials 8, 365 (2023).

[2] Nature Reviews Chemistry 9, 208 (2025).

[3] Nature Materials 22, 977 (2023).

[4] Advanced Materials 35, 2302279 (2023).

[5] Nature 643, 675 (2025).

Perovskite photodetectors show tremendous promise, yet traditional hole transport layers such as PEDOT:PSS often induce interfacial defects and energy mismatches that limit device performance¹. To overcome these HTL-related bottlenecks, this study proposes a systematic device engineering approach. First, we demonstrate that de-doping PEDOT:PSS using DBU effectively mitigates interfacial issues and enhances initial device performance². To fundamentally eliminate HTL-induced instability, we further develop an HTL-free architecture based on MAPbI₃. Since the direct removal of the HTL compromises the intrinsic electron-blocking capability, we introduce an n-type doping strategy into the perovskite layer. This n-doping effectively induces favorable interfacial band bending, restoring charge selectivity, suppressing dark current³, and significantly boosting the performance of HTL-free devices. Finally, to extend the detection range to the near-infrared region, we implement this "HTL-free and n-doped" strategy in narrow-bandgap tin-lead perovskites. The optimized Sn-Pb photodetectors demonstrate a remarkably suppressed dark current and an outstanding ON/OFF ratio, achieving superior NIR sensing capabilities⁴. This work provides a robust pathway for designing high-performance perovskite photodetectors for NIR detection.

Halide perovskites have emerged as promising candidates for next-generation optoelectronic devices owing to their superior optical and electronic characteristics. Yet, their practical deployment is severely limited by instability under ambient conditions. In this work, we demonstrate a simple room-temperature in-situ encapsulation approach, where a silica shell derived from (3-aminopropyl)triethoxysilane (APTES) significantly improves both the stability and luminescence of CsPbBr₃ nanosheets. Structural analysis (XRD) confirms the preservation of the orthorhombic phase, while FTIR and transient absorption spectroscopy reveal effective surface passivation. The optimized CsPbBr₃–SiO₂ film, obtained with 1 µL APTES, delivers a ~17-fold increase in photoluminescence intensity and maintains durability against continuous UV irradiation, thermal stress (60 °C), and ambient exposure for over three weeks. Furthermore, integration with gold and silver nanoparticles enables plasmonic modulation of optical and device performance. Notably, the AuNP-coupled CsPbBr₃–SiO₂ nanosheets exhibit remarkable photodetector response with a responsivity of 1.06 × 10² A/W and a detectivity of 2.71 × 10⁸ Jones. These results highlight an effective strategy for stabilizing halide perovskite nanostructures while tailoring their optoelectronic properties, paving the way toward robust, high-efficiency photodetectors.

In the last decade, metal halide semiconductors have emerged as promising materials for solar cell applications. While lead halide semiconductors have achieved remarkable power conversion efficiencies, now exceeding 26%, Pb(II) toxicity and stability issues have raised the urgency of developing stable and environmentally friendly alternatives. As a result, a catalogue of emerging metal halide semiconductors (e.g., 2D perovskites, double perovskites, rudorffites, and others) has been the subject of intense investigation. However, record power conversion efficiencies for this new class of materials currently lag behind those of traditional metal halide perovskites, prompting new research efforts to explore and eliminate current performance limitations. In this talk, I will discuss the impact of electronic and structural dimensionality on charge-carrier transport and recombination in these materials.

I will start by discussing the impact of low (<3D) electronic dimensionality on charge-carrier transport in emerging perovskite-inspired materials. Focusing on the archetypal silver-bismuth-based perovskite-inspired materials (PIMs), I will examine how rapid decays in terahertz photoconductivity and their temperature dependence reveal an ultrafast localisation of free charge carriers to a small polaronic state.[3,4] Examples related to several structural and chemical features of PIMs, such as cation disorder, cation vacancies, and structural dimensionality, will be given.

I will proceed in discussing how the peculiar electronic structure of PIMs, and in cases, the presence of localised states, contribute to determining the charge-carrier recombination dynamics of these materials. In particular, I will focus on quasi-1D bismuth-based semiconductors. I will illustrate how temperature-dependent terahertz photoconductivity can disentangle different contributions to overall recombination, and demonstrate how the resulting mechanism can be investigated by comparing the temperature-dependent absorption coefficient with the terahertz photoconductivity through the van Roosbroeck-Shockley equation.

Overall, achieving efficient charge-carrier transport and slow charge-carrier recombination remains a formidable challenge for low-dimensional electronic and structural materials and their use in renewable energy. The findings presented in this talk explore the underlying causes of these challenges, thus tracing a clear path towards tackling them.