High Open-Circuit Voltage of 1.134 V for Inverted Planar Perovskite Solar Cells with Sodium Citrate-Doped PEDOT:PSS as a Hole Transport Layer

Poly(3,4-ethylenedioxythiophene)/polystyrene sulfonate (PEDOT:PSS) plays an important role in inverted planar perovskite solar cells (IPPSCs) as an efficient hole extraction and transfer layer (HTL). The IPPSCs based on PEDOT:PSS normally display inferior performance with a reduced open-circuit voltage. To address this problem, here sodium citrate-doped PEDOT:PSS is adopted as an effective HTL for improving the performance of IPPSCs. Sodium citrate-doped PEDOT:PSS HTL improves the conversion efficiency of IPPSCs from 15.05% of reference cells to 18.39%. The large increase of the open-circuit voltage (V-OC) from 1.057 to 1.134 V is the main source for this performance enhancement. With the help of characterization analysis of ultraviolet photoelectron spectroscopy, scanning electron microscopy, electrochemical impedance spectroscopy, etc., the higher work function of the doped PEDOT:PSS film and the uniform crystallinity of the perovskite film on it are disclosed as the reasons for the increased V-OC and the consequent performance enhancement.