Discerning Blend Microstructure and Charge Recombination for Stable Biorenewable‐Based Organic Photovoltaics

Abstract The power conversion efficiency of organic photovoltaics (OPV) has recently surpassed 20%. However, the degradation mechanisms affecting blends based on these materials require urgent attention to improve the stability of such devices towards the long timescales necessary for commercialization. In this work, we evaluated the degradation of OPVs based on sustainable and scalable donors poly[(thiophene)‐alt‐(6,7‐difluoro‐2‐(2‐hexyldecyloxy)quinoxaline)] (PTQ10) and poly[(5‐fluoro‐6‐((2‐hexyldecyl)oxy)benzo[c][1,2,5]thiadiazole)‐alt‐thiophene] (FO6‐T) blended with Y‐family NFAs with different side‐chain lengths processed from biorenewable 2MeTHF for PTQ10:Y12 and FO6‐T:Y12 and from chloroform for FO6‐T:Y6 blends. Superior stability is observed for FO6‐T:Y12 with an extrapolated T80 of over 2000 h under LED illumination, and a more stable trend under metal halide lamps illumination compared to the other blends. By analyzing the thin film microstructure using Atomic Force Microscope (AFM), a significant phase separation is observed in the Y6‐based blend, compared to PTQ10:Y12 and FO6‐T:Y12, and a clear red‐shift in the UV–vis profile. The superior stability of the FO6‐T:Y12 blend is attributed to less morphological degradation upon aging and the increased number of photogenerated charges upon degradation. Finally, through a series of light intensity and temperature‐dependent J–V characterizations, we evaluated the recombination mechanisms.