Enhancing the Stability and Efficiency of Tin-Based Perovskite Solar Cells via Bifunctional Additive-Engineered Defect Passivation

Tin-based perovskites have been recognized as an optimal alternative to lead-based perovskites in the photovoltaic field due to their nontoxic nature and excellent optoelectrical properties. However, the efficiency and stability of tin-based perovskite solar cells (Sn-PSCs) as competing requirements are significantly worse than those of their lead-based counterparts, primarily due to the poor perovskite layer quality, Sn²⁺ oxidation, and high defect density. Herein, cyanamide (CA) with -C≡N and -NH₂ groups is introduced as a multifunctional additive to the precursor solution of Sn-PSCs to improve crystallinity and suppress microstructure defects. A series of characterizations demonstrates that the CA molecules have strong interactions with Sn²⁺ and I^-, thereby suppressing Sn²⁺ oxidation and migration of I^-. The CA additives result in reduced defect density and inhibit carrier recombination. Consequently, the Sn-PSCs modified by CA additives (CA-modified PSC) achieve a champion PCE of 11.74%, which is much higher than 7.32% of the control devices. Significantly, the exposure of unencapsulated CA-modified PSC to a N₂ atmosphere for 5000 h does not affect their initial efficiency, while the control devices show only 63% of their original efficiency. This work provides a straightforward and effective strategy for the development of efficient and stable Sn-PSCs.