Understanding the correlation and balance between the miscibility and optoelectronic properties of polymer-fullerene solar cells

Organic photovoltaics is one of the most promising technologies for sustainable green energy supply. Because of their high electron affinity and superior electron-transporting ability, fullerene-based materials are deemed as very strong electron-accepting components in organic solar cells. However, the most widely used fullerene-based acceptors, such as phenyl-C61-butyric acid methyl ester, exhibit limited microstructural stability and unsatisfactory thermal stability owing to their insufficient compatibility with organic donors. Here, we in-depth investigate the carrier dynamics along with structural evolution and analyze the acceptor loadings in optimized bulk-heterojunction (BHJ) solar cells as a function of the polymer-fullerene miscibility. The polymer-fullerene miscibility has more influential effects than the crystallinity of single components on the optimized acceptor : donor ratio in polymer-fullerene solar cells. The findings demonstrated in this work suggest that the balance between the miscibility of BHJ composites and their optoelectronic properties has to be carefully considered for future development and optimization of OPV solar cells based on BHJ composites. Miscibility is proposed in addition to crystallinity as a further design criterion for long lived and efficient solar cells.