In-Situ Electropolymerized Polyamines as Dopant-Free Hole-Transporting Materials for Efficient and Stable Inverted Perovskite Solar Cells

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.