Multifunctional RbCl dopants for efficient inverted planar perovskite solar cell with ultra-high fill factor, negligible hysteresis and improved stability

Interfacial engineering, especially for the hole transport layer (HTL) design, is a significant approach to improve photovoltaic performance of inverted planar perovskite solar cells (PSCs). Herein, we decorated the widely used HTL materials of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) through dispersing rubidium chloride (RbCl) in the aqueous solution. Based on systematic characterizations, we find that the RbCl dopant plays multiple roles in both the PEDOT:PSS-RbCl composite film and the interface between perovskite and HTL. RbCl could induce phase segregation of PEDOT:PSS and enlarge its nanocrystal size, which in turn to simultaneously enhance electrical conductivity, hole transport capability and work function without sacrificing optical transmittance of the HTL. In addition, RbCl crystallite possesses similar polyhedral structure and lattice parameters as the perovskite, which is beneficial for the seed-mediated growth of perovskite. The seed-mediated perovskite formation leads to a dense and uniform active layer with superior crystallinity and less trap density. Consequently, the PSCs with the doped HTL show remarkably enhanced performance for both the pure perovskite MAPbI3 (from 13.24% to 16.63%) and mixed perovskite MA0.7FA0.3Pb(I0.9Br0.1)3 (from 16.13% to 18.30%). Impressively, negligible hysteresis, high fill factor (FF, over 80%) and improved moisture stability are observed for both perovskites using the doped HTL.