Tunable Molecular Packing of Dopant-Free Hole-Transport Polymers for Perovskite Solar Cells

Optimizing the molecular packing and orientation of dopant-free hole-transport materials (HTMs) to promote their charge transport is a challenging but effective strategy for achieving high-performance perovskite solar cells (PSCs). Here, we successfully demonstrated tunable molecular packing and orientation of polymers by regulating the donor building blocks by shifting the conjugated side chain to the main chain and using a large core unit. The conjugated polymer we developed, namely PC-DPP, with a thiophene-substituted phenanthrocarbazole (PC-T) as a donor unit and diketopyrrolopyrrole (DPP) as an acceptor unit, shows a preferred face-on orientation. By contrast, the control PBDT-DPP polymer shows a preferred edge-on orientation. As a result, the PC-DPP film shows enlarged hole mobility and strengthened interfacial contact with the perovskite surface. Consequently, in contrast to the PBDT-DPP HTM, the device using dopant-free PC-DPP dramatically improved the efficiency from 17.27% to 22.67%. This work paves a new path for developing dopant-free HTMs.