Conquering the morphology barrier of ternary all-polymer solar cells by designing random terpolymer for constructing efficient binary all-polymer solar cells

The ternary strategy based on two electron donors and one electron acceptor can effectively expand the absorption and photovoltaic performance of all-polymer solar cells (all-PSC). However, it is still challenging to realize the ideal morphology of the ternary blend film through reasonable molecular design. To overcome the morphology barrier of ternary all-PSC, here we replaced physical blending of two donors (P1 and P2) by chemical random ternary copolymerization obtaining a terpolymer namely P1-co-25%P2. The binary all-PSCs constructed by integrating P1-co-25%P2 with a polymerized non-fullerene acceptor PYFT exhibited an impressively high power conversion efficiency (PCE) of 14.67%, which obviously outperformed those of obtained from ternary all-PSCs based on P1:P2:PYFT. Further morphology characterization of these blend films revealed that the incorporation of the P2 unit in the P1 backbone can optimize the π-π stacking, miscibility and phase separation that beneficial to exciton diffusion and charge transport, illustrating the unparalleled superiority of the random ternary copolymerization strategy compared to the ternary blending strategy.