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

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 & omega; for 1MEO-Spiro-OMeTAD, and 3815.3 & omega; 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. This study involves the replacement of acetonitrile (ACN) in Spiro-OMeTAD with 1-methoxy-2-propanol (1MEO) and 2-ethoxy-ethanol (2ETO). These solvents improve hole mobility in Spiro-OMeTAD, reducing defects at the perovskite/Spiro-OMeTAD interface and nonradiative recombination. This leads to higher device efficiencies of 21.3% and 20.0% for 1MEO and 2ETO, compared to ACN (18.9%). Modified devices demonstrate better stability during a 45 d test.image & COPY; 2023 WILEY-VCH GmbH