Development of cross-linked donor polymers for polymer solar cells with improved efficiency and thermal stability

Due to low glass-transition temperature and high diffusion coefficient of small molecule acceptors (SMAs), the bi-continuous interpenetrating morphology of SMAbased polymer solar cells (PSCs) are metastable and therefore most SMA-based PSCs exhibit poor operational and thermal stability. Cross-linked donor polymers have been proposed because the cross-linked behavior can "freeze" the initial morphology and avoid its further evolution. In this work, two new cross-linked donor polymers P1 and P2 were designed for application in PSCs with a non-fullerene acceptor Y6, in which the photovoltaic performance and thermal stability of PSCs were significantly improved. The P1-based PSCs achieved a superior power conversion efficiency (PCE) of 17.29% with a J sc of 25.99 mA cm(-2), a V-oc of 0.860 V and a FF of 77.35%, which surpassed 9% for PM6-based PSCs (15.86 %). Furthermore, the P1-based PSCs exhibited better thermal stability with a 17% efficiency loss under continuous 60 degrees C for 210 h due to the fixation of active layer morphology, while PM6-based PSCs suffered from a serve PCE reduction of over 26 %. These results demonstrate that cross-linked donor polymer has a great application prospect to improve the PCE and thermal stability of PSCs.