RESUMEN
Organic photovoltaics (OPV) has been considered for a long time a promising emerging solar technology. Currently, however, market shares of OPV are practically non-existent. A detailed meta-analysis of the literature published until mid-2021 is presented, focusing on one of the remaining issues that need to be addressed to translate the recent remarkable progress, obtained in devices' performance at lab-scale level, into the requirements able to boost the manufacturing-scale production. Namely, the active layer's thickness is referred to, which, together with device efficiency and stability, represents one of the biggest challenges of this technological research field. Papers describing solar cells containing non-fullerene acceptor (NFA) binary and ternary blends, as well as NFA plus fullerene acceptor (FA) ternary blends are reviewed. The common ground of all analyzed devices is their high-thickness active layers, compatible with large-area deposition techniques. By defining a new figure of merit to discuss the OPV thickness (thickness tolerance, TT), it is found that this parameter is not affected by the chemical family's nature of the active blend components. On the other hand, the analysis suggests that there are promising strategies to improve the TT, which are discussed in the conclusion section.
RESUMEN
The photochemical stability of encapsulated films of mixed halide perovskites with a range of MAPb(I1-x Brx )3 (MA=methylammonium) compositions (solid solutions) was investigated under accelerated stressing using concentrated sunlight. The relevance of accelerated testing to standard operational conditions of solar cells was confirmed by comparison to degradation experiments under outdoor sunlight exposure. We found that MAPbBr3 films exhibited no degradation, while MAPbI3 and mixed halide MAPb(I1-x Brx )3 films decomposed yielding crystallization of inorganic PbI2 accompanied by degradation of the perovskite solar light absorption, with faster absorption degradation in mixed halide films. The crystal coherence length was found to correlate with the stability of the films. We postulate that the introduction of Br into the mixed halide solid solution stressed its structure and induced more structural defects and/or grain boundaries compared to pure halide perovskites, which might be responsible for the accelerated degradation. Hence, the cause for accelerated degradation may be the increased defect density rather than the chemical composition of the perovskite materials.
