Energy Level Tuning of PEDOT:PSS for High Performance Tin-Lead Mixed Perovskite Solar Cells

Small bandgap Sn-Pb mixed perovskite is generally regarded as the most promising structure to further enhance the power conversion efficiency of perovskite solar cells. However, the open circuit voltages (V(OC)s) are usually lower than expected. In this work, by doping the generally used hole transporting layer (HTL) poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) with a perfluorinated ionomer (PFI), we can tune the work function of it from -5.02 to -5.19eV. This reduces the energy level mismatch between the FA(0.6)MA(0.4) Sn0.6Pb0.4I3 (FAMA) absorber and HTL, giving rise to enhanced built-in voltage and better carrier extraction. The V-OC improves to over 50mV, up to 0.783V, resulting in an improved champion power conversion efficiency (PCE) of 15.85%. Moreover, the devices based on modified HTLs show improved stability at maximum power point. These results demonstrate that energy level tuning of the HTL is a promising strategy for the improvement of the PCEs of Sn-Pb mixed inverted PSCs, and the addition of PFI is an effective method to tune the work function of PEDOT:PSS.