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.

Currently, there is an urgent need to develop low-cost hole-transporting materials (HTMs) for inverted perovskite solar cells (PSCs), whose power conversion efficiency (PCE) is still inferior to those with a regular device structure. Herein, we report the successful application of in-situ electropolymerized polyamine films as dopant-free HTMs for efficient and stable inverted PSCs. The oxidative electropolymerization of a readily available star-shaped monomer 1, with a pyrene core and four triphenylamine side arms, affords poly-1 films with networked structures and strong hydrophobicity. A device configuration of ITO/poly-1/(FAPbI3)x(MAPbBr3)(1-x)/PC61BM/BCP/Ag is adopted to yield the best PCE of 16.5%, comparable to that of the device with undoped PTAA as the HTM under the same conditions; however, its steady-state output exhibits distinctly better stability than that of the PTAA-based device. This represents the best performance reported to date of electropolymerized HTMs in PSCs. The dependence of the electropolymer film thickness on the photovoltaic performance reveals an optimal HTM thickness of around 50 nm. Moreover, the PSCs containing poly-1 as the dopant-free HTM exhibit good long-term stability under ambient conditions (91% efficiency is retained after 1000 h) as compared to devices with PTAA. This work offers an avenue for developing cost-effective and stable electropolymerized polyamines as HTMs for high-performance PSCs and other optoelectronic devices.

Although perovskite solar cells (PSCs) have achieved remarkably high efficiency (25.7%), their long-term stability still needs to be addressed for commercial applications. As an important part of PSCs, hole-transporting layer...