Importance of Functional Groups in Cross-Linking Methoxysilane Additives for High-Efficiency and Stable Perovskite Solar Cells

Here we report an efficient and reproducible multifunctional additive engineering strategy via methoxysilane cross-linking agents functionalized by the different terminal group, moderate electron-donating -SH, weak electron-donating -CH₃, or strong electron-withdrawing -CN, into a PbI₂ precursor solution. The power conversion efficiency (PCE) is increased from 18.4 to 20.8% after introduction of (3-mercaptopropyl)trimethoxysilane (MPTS) containing a -SH group as a consequence of improved voltage and current density, while 3-cyanopropyltriethoxysilane (CPTS) containing a -CN group deteriorates the overall photovoltaic performance. Moreover, -SH in MPTS is found to passivate defects effectively through a Lewis acid-base interaction with PbI₂, resulting in a larger grain size and a longer carrier lifetime. Owing to the formation of a cross-linking siloxane network as a protective layer on the grain boundary, the thermal and moisture stability of the device are improved remarkably. The present work provides a guideline for multifunctional additive engineering for the purpose of simultaneous achievement of a high PCE and long-term stability.