Defect mitigation via fullerene-based functional additives for enhanced efficiency and stability in tin perovskite solar cells

Abstract

Tin-based perovskite solar cells (Sn-PSCs) represent a promising lead-free alternative for photovoltaic applications, however, their oxidation of Sn²⁺ to Sn⁴⁺, induces structural defects and compromises device stability and efficiency. In this study, we introduced fullerene-based multifunctional molecules (F-COOH, F-OH, F-OSO₃H) as additives to interact with Sn²⁺ ions, effectively stabilizing tin in its reduced state. These functional additives affect the growth and optoelectronic properties of tin perovskite film. Among these additives, F-COOH significantly suppresses Sn⁴⁺ formation and non-radiative recombination. Consequently, the device with the F-COOH additive exhibits an increased power conversion efficiency (PCE) from 8.20 to 11.22%, along with improved reproducibility and stability. While additives with –OH and –OSO₃H functional groups also enhance performance, the superior results with F-COOH are attributed to the localized electron density provided by the –COOH group, facilitated by its connection to the fullerene core through a sp³ hybridized carbon. Device analysis indicated that the F-COOH additive enhances the optoelectronic properties of Sn-PSCs, contributing to a higher diffusion potential while effectively minimizing bulk and interfacial defects. Thus, this work underscores the importance of functional group selection in molecular design to improve the efficiency and stability of Sn-PSCs, paving the way for advanced lead-free solar cell technologies.