Efficient and flexible solar cells with improved stability through incorporation of a multifunctional small molecule at PEDOT:PSS/perovskite interface

Inverted perovskite solar cells based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) have drawn great attention due to their potential for foldable photovoltaic applications. Modification of the interface of PEDOT:PSS and perovskite layer is one of the approaches for improving the efficiency and stability. Here, we introduce a triphenylamine-based small molecule, N,N'-Bis-(1-naphthalenyl)-N,N'-bis-phenyl-(1,1'-biphenyl)-4,4'-diamine (NPB), into the device as the multifunctional buffer layer. It is noted that the NPB buffer layer can obviously reduce the pinholes and defects of perovskite film, and adjust the energy level mismatch between perovskite and PEDOT:PSS layer. Moreover, the carrier recombination of NPB-modified device is restricted due to the reduced defects in perovskite layer and at PEDOT:PSS/perovskite interface. As a result, the device power conversion efficiency is improved from 15.4% to 18.4%. The flexible devices are further fabricated with the best efficiency of 14.4% without hysteresis. Most importantly, due to the superior moisture and UV-light resistance of NPB, the modified device exhibits excellent long-term stability under ambient atmosphere and UV-light soaking.