An n‐doping cross‐linkable quinoidal compound as a new type of electron transport material for fully stretchable inverted organic solar cells

The photocatalytic activity and inherent brittleness of ZnO, which is commonly used as an electron transport layer (ETL) in inverted organic solar cells (OSCs), have impeded advancements in device stability and the development of fully stretchable OSCs. In this study, we have developed an intrinsically stretchable ETL for inverted OSCs through a side‐chain cross‐linking strategy. Specifically, cross‐linking between bromine atoms on the side chains of a quinoidal compound and the amino groups in polyethylenimine resulted in a film, designated QBr‐PEI‐50, with high electrical conductivity (0.049 S/m) and excellent stretchability (crack‐onset strain >45%). When used as the ETL in inverted OSCs, QBr‐PEI‐50 was markedly superior to ZnO in terms of device performance and stability, yielding a power conversion efficiency (PCE) of 18.27% and a T80 lifetime exceeding 10000 h. Moreover, incorporation of QBr‐PEI‐50 in fully stretchable inverted OSCs yielded a PCE of 14.01%, and 80% of the initial PCE was maintained after 21% strain, showcasing its potential for wearable electronics.