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

Optimizing the molecular packing and orientation of dopant-freehole-transport materials (HTMs) to promote their charge transportis a challenging but effective strategy for achieving high-performanceperovskite solar cells (PSCs). Here, we successfully demonstratedtunable molecular packing and orientation of polymers by regulatingthe donor building blocks by shifting the conjugated side chain tothe main chain and using a large core unit. The conjugated polymerwe developed, namely PC-DPP, with a thiophene-substituted phenanthrocarbazole(PC-T) as a donor unit and diketopyrrolopyrrole (DPP) as an acceptorunit, shows a preferred face-on orientation. By contrast, the controlPBDT-DPP polymer shows a preferred edge-on orientation. As a result,the PC-DPP film shows enlarged hole mobility and strengthened interfacialcontact with the perovskite surface. Consequently, in contrast tothe PBDT-DPP HTM, the device using dopant-free PC-DPP dramaticallyimproved the efficiency from 17.27% to 22.67%. This work paves a newpath for developing dopant-free HTMs.

Automated summary

Optimizing the molecular packing and orientation of dopant-free hole-transport materials (HTMs) is an effective strategy for achieving high-performance perovskite solar cells (PSCs). By regulating the donor building blocks and using a large core unit, we successfully demonstrated tunable molecular packing and orientation of polymers. The developed PC-DPP conjugated polymer with a preferred face-on orientation showed enlarged hole mobility and improved efficiency in PSCs compared to the control PBDT-DPP polymer with a preferred edge-on orientation. This work opens up possibilities for developing dopant-free HTMs.