Defect-Stabilized Tin-Based Perovskite Solar Cells Enabled by Multifunctional Molecular Additives

Sn-based perovskite solar cells (Sn-PSCs) are the most viable replacements for Pb-based PSCs. However, the facile oxidation of Sn 2+ and a high defect density on the surfaces and grain boundaries in Sn-PSCs complicate the task of attaining highly stable Sn-PSCs. Here, both surfaces and grain boundaries are passivated using a fulleropyrrolidine with a triethylene glycol monoethyl ether side chain (PTEG-1) as a multifunctional molecular additive for the first time. The ether group and fullerene group in PTEG-1 interact with Sn 2+ and I –, respectively, thereby inhibiting the formation of Sn 4+ and I 3 – . This multifunctional passivation suppresses nonradiative recombination and improves the stability of Sn-PSCs. As a result, Sn-PSCs with encapsulation retain 65% of their initial power conversion efficiency after 1000 h of light illumination under ambient conditions. Our results provide a guideline for the future design of multifunctional molecules with functional groups that enable the fabrication of stable Sn-PSCs.