Morphology optimization via molecular weight tuning of donor polymer enables all-polymer solar cells with simultaneously improved performance and stability

Organic solar cells with excellent device performance and stability are essential for both academic and industrial purposes. The molecular weight (Mn) of donor polymers plays a critical role in determining the photovoltaic properties of all-polymer solar cells (all-PSCs). Despite Mn of donor polymers has pronounced effects on microstructure morphology, photovoltaic performance and stability of all-PSCs are rarely analyzed and understood in high-performance devices. In this study, we systematically investigate the influence of Mn of donor polymers on the device performance metrics and device stability of all-PSCs comprising of a wide-bandgap polymer donor PTzBI-Si and a polymer acceptor N2200. All-PSCs based on high Mn of PTzBI-Si exhibit an excellent PCE of 11.5% with improved stability, which is clearly superior to that of all-PSCs based on low Mn of PTzBI-Si. The photovoltaic performance difference caused by Mn of PTzBI-Si is systematically characterized and analysed to establish the morphology-property-performance correlation. The findings demonstrated in our model system suggest that tuning the Mn of donor polymer could be a facile and promising strategy to simultaneously enhance the efficiency and stability of all-PSCs.