The performance and long-term stability of organic solar cells are intimately linked to the nanoscale and mesoscale structures that emerge during thin-film formation. In donor–acceptor blends, molecular packing, phase separation, and domain connectivity collectively determine the efficiency of charge generation, transport, and extraction. However, controlling these structural features remains a central challenge, as they originate from a sequence of complex and interconnected processing steps, beginning with the molecular aggregation state in solution [1,2], followed by rapid structure formation during deposition [2], and completed through post-treatments such as thermal or solvent annealing [3,4]. Understanding and actively steering these transitions is therefore key to realizing both high efficiency and operationally stable devices. In this talk, I will highlight how structure formation governs performance- and stability-relevant processes in state-of-the-art OPV systems, drawing on recent examples. Using time-resolved and multimodal characterization approaches—most prominently grazing-incidence X-ray scattering and optical spectroscopy—we track the evolution of aggregation during and after film deposition. These measurements reveal how subtle variations in ink formulation, solvent evaporation pathways, and annealing conditions lead to distinct hierarchical morphologies. Such multiscale structures not only set the energetic landscape and charge-transport pathways in high-performance devices, but also predetermine how the material will respond to e.g. thermal stress during operation.

A particularly instructive example comes from our recent temperature-dependent study of PM6-based systems [4], where controlled heating allowed us to disentangle reversible from irreversible structural changes and relate differences in behaviour to the structural differences obtained during structure formation.

Looking ahead, I will further demonstrate that the integration of automated, high-throughput characterization and data-driven analysis offers a powerful route to further accelerate our understanding of structure–stability relationships in OPV materials.

Polymer solar cells (PSCs) have been considered as a promising photovoltaic technology for sustainable energy harvesting owing to their flexibility, low cost, and potential for large-scale applications. The development of non-fullerene acceptors has enabled PSCs to achieve a power conversion efficiency exceeding 21%, highlighting the excellent industrial potential of this emerging solar technology. Despite these efficiency gains, the long-term stability of PSCs remains a significant challenge that hinders their commercial viability.

The research team in SINANO has been working on the intrinsic degradation mechanisms of polymer solar cells under light, heat and electric field stress. Especially, we recently developed a spectroscopic method to characterize the chemical components of the polymer blends quantitatively and demonstrated that the non-fullerene acceptor-based polymer blends are intrinsically thermally stable.[1-2] While the unexpected interfacial degradation at the photoactive layer/MoO₃ interface is responsible for the thermal degradation of polymer:non-fullerene solar cells.[3-4] By proper interfacial protection of the anode interfaces, the cells showed an excellent thermal stability under 85 °C or even 150 °C thermal annealing, that enables the excellent tolerance over damp-heat and thermal cycling tests.[5] Our findings underscore the effectiveness of our approach and provide valuable insights for the design of more stable polymer solar cells.

Polycyclic aromatic molecules, especially perylene diimide based dyes, are widely used as electronic materials in photovoltaic devices.¹ Our team at the University of Calgary has been actively developing modified perylene diimides for use in a range of solution processed electronic devices including organic solar cells,² organic light emitting diodes,³ transistors and sensors,⁴ electrochromic films,⁵ and photo/electro cathodes.⁶ This presentation will detail the design and synthesis of several classes of new molecules for specific use in large area organic photovoltaic devices and modules, primarily as cathode interlayers in both conventional and inverted type cells, but also as non-fullerene acceptors. Structure-property relationships, the formation of functional large area films via slot-die coating using green solvents, and utility both small area devices and flexible modules will be discussed. In addition, this presentation will introduce new ultra-narrow gap molecules for use as electron acceptors.⁷

The power conversion efficiency (PCE) of organic photovoltaics (OPV) has recently surpassed the 20% mark on record cell level (<0.1 cm²), but is still lagging behind for larger devices. Therefore, our research group primarily focuses on the upscaling of such emerging PV technologies from small cell level all the way to large-area modules.

In this talk, the systematic upscaling of OPV devices based on the photoactive system PM6:Y6-C12:PC₆₁BM is presented. All devices are solution-processed in ambient air from non-halogenated solvents. Finite element method (FEM) simulations are used to optimize the layout of large-area cells (1 cm²) and modules >200 cm², to achieve outstanding PCEs of 15.9% and 14.5%, respectively. Furthermore, fully printed semi-transparent modules using silver nanowires as top electrode are developed and optimized regarding transparency and efficiency. Finally, an encapsulation method for such modules is developed and the encapsulated modules are extensively characterized and tested regarding lifetime under different accelerated ageing conditions.

With constant discovery and development of new organic photovoltaic (OPV) materials, the variable parameter space for material and device fabrication expands exponentially. At the same time, successful OPV technology advancement requires optimization of both performance and stability. The challenge is therefore efficiently optimizing fabrication processing and cell architecture variables to intensify focus on the most promising paths forward in an ever-expanding and myriad of options. To address this challenge, we developed HOOPS: High-throughput Optimization of OPVs for Performance and Stability. HOOPS allows the researcher to rapidly optimize all layers of the OPV for performance, thermal stability, and light stability simultaneously. As an example, we used HOOPS on PTQ-10:Y6-BO based devices to quickly identify which processing and post-processing parameters of the active layer and electron transport layer resulted in simultaneous high performance and good stability for the OPV. The results underscore the fact that processing and fabrication parameters for a given OPV are different when the goal of achieving optimal PCE shifts to achieving high PCE and stabile performance. We also demonstrate the value of HOOPS in quickly scaling from spin-coated small-area devices to slot-die printed large-area modules.

Organic photovoltaics (OPV) have emerged as a highly promising technology for agrivoltaics applications due to their intrinsic spectral tunability, mechanical flexibility, lightweight nature, and potential for low-cost manufacturing [1][2]. However, for OPV to become a realistic and scalable solution in agricultural settings, significant challenges related to processability, stability, and large-scale manufacturing need to be addressed [3]. Although laboratory-scale devices can achieve energy conversion efficiencies of up to 21.2 % [4], these values tend to decrease upon area scaling [5]. Despite a few remarkable studies reporting module efficiencies of 14.46% and 18.36% with areas in the range of 15 cm2, [6][7] this scaling lag decreases further in attempts to adapt the modules to certain scenarios, such as the incorporation of flexible substrates, the preparation of semi-transparent and/or printed electrodes, or targeting larger active areas.

This study presents our methodology developed for the fabrication of OPV modules specifically tailored for agrivoltaic use, detailing the steps taken to adapt the technology to this application niche. Three active-layer systems (PTB7-Th:IEICO-4F:PC70BM, PM6:DTY6, and D18:DTY6) were selected based on their spectral compatibility with plant-light requirements and their reported potential for scalable processing. For these systems, the device stack was optimized, including optical transparency, module interconnections, and geometric layout. The process resulted in the fabrication of 100 cm² semitransparent modules with optimized transmittance and efficiencies above 4%. The modules were subsequently evaluated during the growth of Arabidopsis thaliana and Cardamine hirsuta seedlings under controlled conditions, assessing both photovoltaic performance and plant developmental responses. The results highlight the current bottlenecks in scaling OPV, particularly the efficiency losses caused by increasing the active area (which can be up to 30%), the use of a semi-transparent upper electrode, and the integration of series interconnections within modules. In addition, biological tests reveal the influence of spectral modulation on plant development, providing valuable information for future material selection. Overall, this work describes a comprehensive approach to adapting OPV technology to agricultural settings, bridging the gap between laboratory-scale optimization and application-oriented module design.

The development of all-small-molecule organic solar cells (ASM-OSCs) is often hampered by the trade-off between high power conversion efficiency (PCE) and operational stability, leaving numerous high-performance but unstable material systems underutilized. To address this, we established an innovative high-throughput experimental platform, integrating a FLEX automated liquid dispensing system and an automated blade-coating device, enabling rapid and precise screening of multicomponent blends. Leveraging this platform, we implemented a "waste-to-treasure" strategy to revitalize two thermally unstable but efficient systems, MPhS-C2:BTP-eC9 and T27:Y6. By systematically exploring 252 distinct quaternary compositions, we identified an optimal formulation that achieves a champion PCE of 18.38%—ranking among the highest for ASM-OSCs. Crucially, this optimized quaternary blend exhibits exceptional thermal stability, retaining over 90% of its initial PCE after 1000 hours at 120 °C, far surpassing its binary counterparts. Mechanistic studies reveal that the selected blend facilitates a "dispersed crystallization" mechanism, leading to higher nucleation density and a reduced crystallization driving force, which effectively suppresses detrimental phase separation. This work not only delivers a high-performance, thermally stable ASM-OSC but also showcases the power of automated high-throughput screening as a transformative tool for unlocking the latent potential of existing material libraries.

Organic photovoltaics (OPVs) have reached efficiencies exceeding 21%, but these peak performances typically rely on synthetically complex and expensive polymer donors such as PM6 or D18, rigid substrates, small active areas (<<1 cm²), and processing by spin coating. While promising, this approach presents significant barriers to commercial viability, particularly considering that the photoactive layer might constitute the majority of the projected costs of OPV module production. Our research addresses these limitations by developing processing techniques for flexible OPV modules using scalable processing with green solvents and a low-cost photoactive layer in an inverted architecture. We investigate PTQ-10 as the polymer donor, which is synthetically simpler than conventional high-efficiency donors for potentially lower cost high-volume production.  Through control of the vertical phase distribution, achieved by utilizing additives, and implementing a tailored layer-by-layer slot-die coating protocol, we increased the efficiency of inverted OPV devices. Additionally, by optimizing the photoactive layer viscosity for slot-die coating, we improved film consistency and quality, achieving active-area efficiencies exceeding 13% for flexible OPV modules larger than 10 cm². We compare performance and stability to commercially available materials, which currently exceed PTQ10 in performance and stability. We discuss the challenges associated with PTQ10-based inks and the work required to turn it into a competitive commercially viable system. Our work nonetheless demonstrates the highest combination of performance and active area for slot-die coated flexible modules, representing a significant step toward commercially viable OPV technology.

Understanding the relation between photocurrent losses, voltage losses, and the energetics of the active layer is at the heart of current research on organic solar cells (OCS). In particular, achieving a high VOC  requires that energy losses during the exciton-to-free charge conversion is minimized. In fact, it is claimed that state-of-the-art non-fullerene acceptor-based devices efficiently generate photocurrent for a negligible HOMO offset, unlike fullerene-based devices, and that this is one of the reasons for the success of NFA-based solar cells.

Here, we present experimental and theoretical evidence that low-offset DA blends are fundamentally limited by inefficient exciton dissociation. Under realistic conditions, this translates into a minimum HOMO offset of ca. 300 meV, meaning that low offset blends cannot be efficient. We will also address the question of whether (and under what conditions) CT dissociation becomes inefficient. Finally, we will discuss the conditions under which the energy offset can be further reduced without compromising photocurrents.

In novel printed organic solar cells, the device performance depends heavily on the donor–acceptor nanomorphology. We focus on two ways nanomorphology affects organic solar cells. First, we study domain connectivity by gradually diluting the donor material, an aspect of functional morphology that is linked to the tortuosity of charge transport. We observe how this affects charge generation, transport, and recombination in a state-of-the-art model system. Second, we investigate a different approach of linking nanomorphology to performance. Instead of using simple 1-dimensional drift–diffusion simulations, we now combine complex 3-dimensional simulations of realistic bulk heterojunction morphologies with machine learning. This approach has two goals. First, to find realistic solar cell parameters based on 3D models rather than effective ones based on 1D fits. Second, since 3D fitting is very time-consuming, machine learning lets us quickly predict solar cell performance and morphology from limited experimental data, reducing computation time from days to seconds.

Understanding the relationships between processing conditions and printed thin-film morphologies is of paramount significance for the optimized fabrication of organic solar cells. For this purpose, a Phase-Field simulation framework was recently developed to simulate nanostructure formation in solution-deposited organic active layers. The model captures the interplay of crucial physical phenomena (i.e., amorphous demixing, crystallization, evaporation, and hydrodynamics), which shape the film morphologies at the nanoscale, and are responsible for the spatial arrangements of the phase domains that are eventually quenched out of equilibrium.

This talk reviews the different morphology formation regimes predicted by the Phase-Field model for crystallizing organic material mixtures, thereby addressing the fundamental thermodynamic and kinetic factors that control the nanostructural evolution (e.g., amorphous material incompatibility, diffusion-limitations, composition-dependent diffusivity, etc.). The provided insights are subsequently applied to a practical investigation case, namely the elucidation of the mutual influence of crystallization and spinodal decomposition on an organic bulk heterojunction upon a thermal annealing treatment. Simulation results are compared against Scanning Electron Microscopy images of the blend at several annealing stages, and the model predictions are found in excellent agreement with the experiments. This allows to confidently unravel the sequence of structuring processes that take place within the system, and explain under which conditions the thermal treatment is beneficial for the performance of the photovoltaic device.

Overall, the Phase-Field approach is shown to provide a detailed mechanistic comprehension of the phase transformations occurring during the solution-processing of organic photoactive mixtures. Therefore, it presents a very promising potential to derive physically-motivated design strategies for efficient and robust organic solar cell manufacturing.

The conversion of low energy into higher energy photons provides an attractive opportunity to improve solar energy technologies. Several types of thin film materials which can transform two or more low energy excited states into a higher energy one, have been previously developed. Due to the non-linear nature of such optical processes, up-conversion is most efficient at high light intensities, typically well above sunlight intensities (100 mW/cm²). Here, we propose an innovative stacked diode approach relying on novel, low-cost organic- semiconductor materials. The thin-film stack comprises a series of organic NIR photovoltaic stacks, providing sufficient photovoltage to drive an organic light-emitting layer deposited on top. We combine state-of-the-art, vacuum-processable absorbing and emitting systems with careful, simulation-assisted stack engineering. Converting photons from NIR (≤835 nm) to green (530 nm), the stack achieves an external upconversion efficiency (EUE) of 1.9%. Importantly, the EUE stays constant over more than 3 orders of magnitude in intensity, down to less than 1 mW/cm². This presentation will focus on efficiency limiting processes within the layer stack, as well as the potential of this approach for photovoltaic and photocatalytic conversion.

High-throughput optical characterization and analysis are crucial for building digital twins of organic semiconductors, enabling accurate modeling of energetic landscapes and carrier dynamics to accelerate material discovery and device optimization. In this work, we fit time-resolved photoluminescence (TRPL) data of bulk heterojunction organic solar cells (BHJ-OSCs) using a rate-equation framework with seven free parameters, optimized through trust-region Bayesian optimization (TuRBO) combined with gradient-based methods. This approach provides detailed insights into the energies of charge-transfer (CT) and triplet local excited (T) states, as well as their associated rate constants and interfacial decay dynamics. By varying the molecular weight and halogenation of the materials, we find that although reducing the HOMO energy offset between the donor and acceptor increases the triplet formation rate to a level comparable to the charge generation rate, our analysis reveals that the dominant nonradiative losses in BHJ-OSCs originate from CT states, with only minor contributions from T states. Furthermore, reducing the energy offset between local excited (LE) and CT states enhances both PLQY and ELQY by shifting nonradiative decay from CT to LE states, but at the cost of charge generation efficiency. Therefore, comprehensive optimization of energetic and kinetic parameters is essential to balance performance—suppressing nonradiative losses from CT states while leveraging the long lifetime of T states as an energy reservoir.

Organic photovoltaics (OPV) has developed from a laboratory curiosity some decades ago into a technology that is now being successfully commercialized. Certified power conversion efficiencies are exceeding 20% in the laboratory [1] and first commercial modules have passed the same stringent IEC & UL tests used to evaluate the quality and stability of silicon PV, the incumbent technology [2]. With properties like mechanical flexibility and a weight of <2kg/m² as well as tunable absorption/transmission, OPV is in particular suited for the built environment and distributed power generation, and for surfaces standard silicon PV cannot be used on (e.g. curved surfaces, low load bearing constructions, semitransparent windows etc.). These additional markets are estimated to be several TW_p in size [3,4]. At the same time, first life cycle analysis (LCA) data of OPV modules made on real production equipment confirm the long postulated lower environmental impact, e.g. demonstrated less than 25% of the CO2e/Wp per OPV module compared to the average silicon PV module, making OPV greener than any other commercial PV technology [5]. In this presentation, the state-of-the art vacuum-processed OPV is reviewed as well as challenges and opportunities discussed to improve power conversion efficiency in the fab beyond 10% and keeping lifetimes >20 years when rapidly scaling this technology to TW_p.

[1] Chen et al., Nature Materials 24, 444 (2025); Wang et al., Advanced Materials 37, e10378 (2025)
[2] Heliatek GmbH, https://www.heliatek.com/en/media/news/detail/heliatek-achieves-iec-61215-certification-for-lightweight-flexible-heliasolr-solar-film/ & https://www.heliatek.com/en/media/news/detail/heliatek-receives-ul-certification-gateway-to-the-north-american-market/
[3] Joshi et al., Nature Communications 12, 5738 (2020)
[4] Traverse et al., Nature Energy 2, 849 (2017)
[5] Heliatek GmbH, https://www.heliatek.com/en/technology/sustainability/

The efficiency and stability of organic solar cells (OSC) is strongly affected by the morphology of the photoactive layers, whose separated crystalline and/or amorphous phases are kinetically quenched far from their thermodynamic equilibrium during the production process. The formation of these structures and their evolution during the lifetime of the cell remains poorly understood.

In this talk, we show how the bulk-heterojunction (BHJ) morphology formation upon drying and its evolution under thermal loading of OSC can be simulated, using a recently developed phase-field (PF) model.[1] For the first time, this allows to investigate the interplay between all the potentially relevant physical processes (nucleation, growth, grain coarsening, amorphous phase separation, composition-dependent kinetic properties), within a single coherent framework. It is shown how the morphology evolution depends on the thermodynamic and kinetic properties of the donor acceptor blend as well as on the processing conditions. [2-4]^.The possible phase separation pathways and associated morphologies are discussed in detail. The approach is applied to several real material system. In all cases, the simulation results are in very nice agreement with the experimental findings.

Moreover, an original approach allowing to calculate morphology-dependent JV-curves of OSC is presented. It is based on a morphological analysis of the BHJ nanostructure, which allows to calculate morphology-aware descriptors for light absorption, exciton dissociation, charge recombination and mobilities. These descriptors are fed into a standard 1D drift-diffusion model to calculate the JV-curve. Opposite to state-of-the-art approaches based on computationally demanding Master equation, Monte-Carlo or 2D/3D drift-diffusion simulations, morphology-dependent JV-curves for a known morphology can be calculated within less than 1 minute. Using morphology evolution under thermal loading obtained from PF simulations, the performance increase of as-cast films upon thermal annealing, and the performance drop during cell lifetime related to intrinsic stability is calculated. Finally, it is shown how the relationship between BHJ evolution and performance evolution can be fully elucidated.

Overall, this contribution illustrates how advanced simulations can help understanding OSC efficiency and intrinsic stability, thus accelerating the development of 3^rd generation photovoltaics and contribute to the energy transition.

Organic photovoltaics (OPVs) are attracting growing attention as lightweight, flexible, and solution-processable solar energy technologies. However, the morphological instability of the bulk-heterojunction (BHJ) active layer remains a critical challenge to their long-term operational stability. In this study, we systematically investigate the phase evolution resistance of high-performance OPV active layers to reveal the intrinsic factors governing thermal and morphological robustness. Through combined molecular design, in situ structural characterization, and device analysis, we correlate donor–acceptor miscibility and interfacial energy with the dynamic evolution of nanoscale morphology. Further analysis show that the extent of molecular rearrangement under thermal stress strongly influences charge transport and device stability. Note that the active layers includes polymer donor:small moleucle acceptor systems, all-polymer systems and all-small molecule systems. This work provides mechanistic insights and design principles for developing next-generation OPV materials with enhanced phase stability and extended operational lifetimes.

The development of organic solar cells requires simultaneous optimization of photovoltaic performance and long-term thermal stability by controlling the bulk heterojunction nanomorphology, which is often mediated by processing solvents and additives. This study investigates the role of small amphiphilic molecules (AMs) as surfactants in stabilizing the bulk heterojunction morphology of PPDT2FBT:PCBM-based organic solar cells. Our research goal is to understand how the chemical nature of AMs and their interface engineering within the device affect stability and efficiency. We demonstrate that the AM's polar headgroup chemistry is a critical determinant for operational stability, and by strategically applying interface engineering across all major interfaces, we identify optimal scenarios for enhancing both efficiency and device durability. Interface engineering not only improves charge transport and mitigates degradation but also supports large-area fabrication and practical device reliability, addressing prominent challenges for commercialization. These findings provide guidance for future molecular design and interface engineering strategies, contributing to the realization of more robust and reliable organic solar cells.