Defect Passivation by a D–A–D Type Hole-Transporting Interfacial Layer for Efficient and Stable Perovskite Solar Cells

In this work, we present a series of donor–acceptor–donor type of small molecules (BDAD, ODAD, and DDAD) based on the triphenylamine (TPA) and dithienopyrrolobenzothiadiazole (DTPBT) units, which are distinguished by alkyl chains of different lengths grafted on the DTPBT unit, as a hole-transporting interfacial layer for perovskite solar cells (PSCs). The incorporation of the DTPBT units is beneficial for not only carrier transportation but also potential defects passivation via Pb–N/S interactions. A champion power conversion efficiency (PCE) of 22.76% has been achieved on PSCs based on BDAD with the n-butyl side chains. Those devices without encapsulation retain over 96% of their initial PCE for more than 120 days. The improved stability is attributed to the restraint of the generation of δ-phase perovskite as supported by the grazing incidence wide-angle X-ray scattering analyses.