Enhancing the Performance of Carbon-Based All-Inorganic CsPbIBr₂ Perovskite Solar Cells via Na₂SiO₃ Surface Treatment for Passivation of the TiO₂/Perovskite Interface

CsPbIBr₂ has garnered significant interest due to its ideal bandgap and good stability. However, defects formed at the interface between the electron transport layer and the perovskite can lead to increased non-radiative recombination, which negatively impacts both the power conversion efficiency (PCE) of perovskite solar cells and the long-term stability of the cells. Herein, the TiO₂/perovskite interface is modified by adding sodium silicate to passivate the defects on the interface. The introduction of Na⁺ partially reduces Ti⁴⁺ to Ti³⁺ in TiO₂, thereby passivating trap states caused by oxygen vacancy defects and adjusting the energy level alignment between TiO₂ and the perovskite film, enhancing the carrier transport efficiency. Additionally, SiO₃²⁻ can form SiOPb (and Cs) bonds with the undercoordinated Pb²⁺ and Cs⁺ on the surface of the perovskite layer, effectively passivating surface defects of the perovskite film and thereby improving the efficiency of the devices. Ultimately, the carbon-based all-inorganic CsPbIBr₂ perovskite solar cells treated with Na₂SiO₃ exhibit a significantly improved PCE of 10.85% compared to 8.62% of the control sample and achieve a high open-circuit voltage of 1.31 V. With this modification, the devices also demonstrate reduced hysteresis effects and enhanced stability.