Dithieno[3,2-b:2',3'-d]pyrrole Cored p-Type Semiconductors Enabling 20 % Efficiency Dopant-Free Perovskite Solar Cells.

Organic p-type semiconductors with tunable structures offer great opportunities for hybrid perovskite solar cells (PVSCs). We report herein two dithieno[3,2-b:2',3'-d]pyrrole (DTP) cored molecular semiconductors prepared through π-conjugation extension and an N-alkylation strategy. The as-prepared conjugated molecules exhibit a highest occupied molecular orbital (HOMO) level of -4.82 eV and a hole mobility up to 2.16×10-4  cm2  V-1  s-1 . Together with excellent film-forming and over 99 % photoluminescence quenching efficiency on perovskite, the DTP based semiconductors work efficiently as hole-transporting materials (HTMs) for n-i-p structured PVSCs. Their dopant-free MA0.7 FA0.3 PbI2.85 Br0.15 devices exhibit a power conversion efficiency over 20 %, representing one of the highest values for un-doped molecular HTMs based PVSCs. This work demonstrates the great potential of using a DTP core in designing efficient semiconductors for dopant-free PVSCs.