Two Birds with One Stone: Dopant-Free Squaraine Hole-Transporting Material for Perovskite Solar Cell

Developing alternative dopant-free hole-transporting materials (HTM) with a passivation effect and high hole mobility is significant for enhancing the power conversion efficiency (PCE) and stability of the perovskite solar cells (PSCs) with a simplified process. In this work, we report a squaraine HTM 3,4bis(4'-(bis(4-methoxyphenyl)amino)-[1,1'-biphenyl]-4-yl)cyclobut-3-ene-1,2-dione (D12) with a resonance central structure shuttling between electrically neutral dione and charge-separated inner salts. The donor-acceptor-donor type molecule D12 exhibits an extremely strong capacity not only for hole exaction and mobility, but also for the passivation of perovskite defects. This results in a high PCE of 22.32% for D12-based PSCs. After 30 days of aging at a high relative humidity of 65% at 30 degrees C, it remains 90% of its initial PCE. This work offers a strategy of designing dopant-free small-molecule HTM and enhancing the stability and PCE of PSCs.