Stability is one of the most important challenges facing material research for organic solar cells (OSC) on their path to further commercialization. In the high-performance material system PM6:Y6 studied here, we investigate degradation mechanisms of inverted photovoltaic devices. We have identified two distinct degradation pathways: one requires the presence of both illumination and oxygen and features a short-circuit current reduction, the other one is induced thermally and marked by severe losses of open-circuit voltage and fill factor. We focus our investigation on the thermally accelerated degradation. Our findings show that bulk material properties and interfaces remain remarkably stable, however, aging-induced defect state formation in the active layer remains the primary cause of thermal degradation. The increased trap density leads to higher non-radiative recombination, which limits the open-circuit voltage and lowers the charge carrier mobility in the photoactive layer. Furthermore, we find the trap-induced transport resistance to be the major reason for the drop in fill factor. Our results suggest that device lifetimes could be significantly increased by marginally suppressing trap formation, leading to a bright future for OSC.

To develop a detailed understanding about halide perovskite processing from solution, the crystallization processes are investigated during spin coating and slot‐die coating of MAPbI3 at different evaporation rates by simultaneous in situ photoluminescence, light scattering, and absorption measurements. Based on the time evolution of the optical parameters it is found that for both processing methods initially solvent‐complex‐structures form, followed by perovskite crystallization. The latter proceeds in two stages for spin coating, while for slot‐die coating only one perovskite crystallization phase occurs. For both processing methods, it is found that with increasing evaporation rates, the crystallization kinetics of the solvent‐complex structure and the perovskite crystallization remain constant on a relative time scale, whereas the duration of the second perovskite crystallization in spin coating increases. This second perovskite crystallization appears restricted due to differences in solvent‐complex phase morphologies from which the perovskite forms. The work emphasizes the importance of the exact precursor state properties on the perovskite formation. It further demonstrates that detailed analyses of multimodal optical in situ spectroscopy allows gaining a fundamental understanding of the crystallization processes that take place during solution processing of halide perovskites, independent from the specific processing method.

Expensive biodegradable packaging as a preventative measure against continued accumulation of plastic waste in our environment is often in conflict with the need for high performing packaging materials that prevent...

Crystalline and 3D continuous mesoporous quaternary CsTaWO6 semiconductors are prepared with different degrees of long‐range periodic order and local order, respectively, to investigate the influence of periodic pore order on the photocatalytic performance in hydrogen evolution of mesoporous photocatalysts. The degree of long‐range order of the mesopores is changed by modifying the ratio between metal precursors and soft polymer template poly(isoprene‐b‐styrene‐b‐ethylene oxide) (PI‐b‐PS‐b‐PEO; ISO) in the sol–gel synthesis. Long‐range periodic order is found to have no appreciable advantage compared with an only locally ordered continuous pore system. On the contrary, nonperiodically ordered mesopores result in higher activity toward photocatalytic hydrogen evolution, even with slightly smaller pore diameter and lower cumulative pore volume. Most importantly, it is shown that pore connectivity and heterogeneous pore systems in mesoporous photocatalysts play a major role for hydrogen evolution when other parameters are confirmed to be not rate limiting.

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Preparing halide perovskite films by solvent‐free, powder‐based processing approaches currently attracts more and more attention. However, working solar cells employing dry, powder‐based halide perovskite thin films, have not been demonstrated so far. Herein, perovskite solar cells are presented where the absorber layer is prepared by transferring readily synthesized perovskite powders into a compact thin film using a fully dry‐powder‐processing concept. Compact thin films are deposited via an optimized powder aerosol deposition (PAD) process. Pressing at 120 °C further improves the morphology and the optoelectronic film properties. Integrating the perovskite films in a solar cell configuration results in fully working devices, with champion power conversion efficiencies of >6%. While the (optoelectronic) properties of the PAD‐processed films are found to be comparable with their solution‐processed counterparts, investigations of the solar cell stack suggest deterioration of the electron‐transport layer properties due to the PAD process, and the presence of hydrates at the perovskite surface to be important factors that contribute to the limited solar cell efficiency. Herein, perspectives to overcome the identified limitations are outlined, emphasizing the high potential and realizability of efficient perovskite solar cells based on dry‐powder‐processing approaches in the future.

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