Efficient and Stable Tin Perovskite Solar Cells by Pyridine-Functionalized Fullerene with Reduced Interfacial Energy Loss

In tin perovskite solar cells (PSCs), fullerene (C₆₀) and fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are commonly utilized electron transport materials. However, the energetic disorder, inadequate passivation, and energy level mismatch of C₆₀ and PCBM limit the improvement of power conversion efficiency (PCE) and lifespan of tin PSCs. In this work, a multifunctional interface manipulation strategy is developed by introducing a pyridine-functionalized fullerene derivative, fullerene-n-butyl-pyridine (C₆₀-BPy), into the interface between the tin perovskite and the electron transport layer (ETL) to improve the photovoltaic performance and stability of tin PSCs. The C₆₀-BPy can strongly anchor on the perovskite surface via coordination interactions between the pyridine moiety and the Sn²⁺ ion, which not only reinforces the passivation of the trap-state within the tin perovskite film, but also regulates the interface energy level alignment to reduce non-radiative recombination. Moreover, the improved interface binding and carrier transport properties of C₆₀-BPy contribute to superior device stability. The resulting devices have achieved the highest PCE of 14.14% with negligible hysteresis, and are maintained over 95% of their initial PCE under continuous one-sun illumination for 1000 h.