Recent Progress in All-Polymer Solar Cells Based on Wide-Bandgap p-Type Polymers.

All-polymer solar cells (all-PSCs), with the photoactive layer exclusively composed of polymers as both donor and acceptor, have attracted growing attention due to their unique merits in optical, thermal and mechanical durability. Through the combined strategies in materials design and device engineering, recently the power conversion efficiencies of single-junction all-PSCs have been boosted up to 11 %. This review focuses on the recent progress of all-PSCs comprising of wide band-gap p-type polymers, especially those based on the units of thieno[3,4-c]pyrrole-4,6(5H)-dione], fluorinated benzotriazole, benzo[1,2-c:4,5-c']dithiophene-4,8-dione, and pyrrolo[3,4-f]benzotriazole-5,7(6H)-dione. Meantime, several categories of n-type polymers used to match with these polymer donors are also reviewed. Finally, a brief summary of the strategies of molecular design and morphology optimization is given, and strategies toward further improving performance of all-PSCs are outlined.