Guanidinium Iodide-Modified PEDOT:PSS Hole Transport Layer for Improving the Performance of 2D Perovskite Solar Cells

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been widely used as a hole transporting layer (HTL) in two-dimensional (2D) Ruddlesden-Popper perovskite (RPP)-based solar cells (2D-PSCs) due to its simple preparation process and low cost. However, the devices based on PEDOT:PSS exhibit low efficiency and poor stability due to the number of buried interfacial defects, energy level mismatching, and corrosivity of the HTL. In this study, a guanidinium iodide (GAI)-modified PEDOT:PSS HTL was adopted to tune the crystallization of 2D RPPs, leading to the formation of 2D perovskite films with preferential crystal orientation, improved crystallinity, and suppressed defect density. The addition of GAI not only enhances the conductivity and intrinsic stability of PEDOT:PSS layers but also improves their energy level matching with those of 2D perovskite films. Upon GAI doping into PEDOT:PSS, the power conversion efficiency of 2D-PSCs increased from 13.11% to 16.04% and maintained 80% of its initial value under 65% relative humidity condition for 60 days. This work demonstrates a novel synergetic modification strategy and gives new insight into the underlying mechanism, which should lead to further improvements in the performance of 2D-PSCs and other optoelectronic devices based on 2D RPPs.