Stability of all-polymer solar cells

The stability of several all-polymer solar cell systems has been assessed and compared to that of representative polymer/fullerene and polymer/small molecule non-fullerene acceptor systems. All-polymer solar systems are found to exhibit superior thermal stability with some systems able to retain > 95% of their starting efficiency after 500 thermal heating cycles (cycling between room temperature and 85 °C). In contrast, the representative polymer/fullerene and polymer/small molecule non-fullerene acceptor systems studied dropped to 70% of their starting efficiency after a few thermal cycles. Two all-polymer systems are also shown to exhibit high stability under elevated temperature, showing no drop in performance when annealed to 200 °C. Microstructural studies of all-polymer systems show minimal change in thin film crystallinity and morphology with annealing to 200 °C in contrast to the polymer/fullerene and polymer/small molecule non-fullerene acceptor systems which show strong aggregation and/or crystallisation of the acceptor phase. Light soaking studies, however, find that the all-polymer systems studied show poor stability under continuous 1 sun illumination, with T80 lifetimes of less than 5 hours. Solving issues to do with stability under illumination is the most pressing need facing the practical application of all-polymer solar cells.