Solvent Engineering of Hole‐Transport Layer for Improved Efficiency and Stability in Perovskite Solar Cells

Abstract

Although perovskite solar cells (PSCs) are one of the fastest‐growing photovoltaic technologies, many innovations are required to further improve performance and stability. The acetonitrile (ACN) solvent used to dissolve the Li‐TFSI salt in Spiro‐OMeTAD corrodes the perovskite thin film. In this study, 1‐methoxy‐2‐propanol (1MEO) and 2‐ethoxy‐ethanol (2ETO) solvents are used by replacing ACN. The utilization of 1MEO results in improved hole mobility in Spiro‐OMeTAD and reduction in defects at the perovskite/Spiro‐OMeTAD interface, thus diminishing nonradiative recombination. The recombination resistances in the low‐frequency range are determined via electrochemical impedance spectroscopy (EIS) and are found to be 3361.9 ohms for ACN‐Spiro‐OMeTAD, 4406.8 Ω for 1MEO‐Spiro‐OMeTAD, and 3815.3 Ω for 2MEO‐Spiro‐OMeTAD. These results indicate that the utilization of 1MEO and 2ETO instead of ACN effectively decreases charge recombination in PSCs. As a result, after replacing ACN with 1MEO and 2ETO, PSCs achieve a power conversion efficiency (PCE) of 21.3% and 20.0% respectively, while a PCE of 18.9% is obtained from the control device with ACN. During 45 d stability test, the initial efficiency of the control device decreases by 31.2%, while the 1MEO and 2ETO devices exhibit efficiency reductions of 12.2% and 7.7%, respectively.