A near-surface sulfidation regulation strategy for inverted inorganic perovskite solar cells with 21.21% efficiency

Inverted inorganic perovskite solar cells (IPSCs) have garnered significant attention in recent years due to their optimal bandgap and exceptional thermal stability. However, the energy level mismatch between the perovskite light-absorbing layer and the commonly employed electron transport layer (ETL) within the inverted structure is relatively pronounced, further exacerbating performance degradation at the upper interface of the inverted device. Here, we present a near-surface sulfidation regulation (NSSR) strategy that employs 2-methylmercaptobenzothiazole (2-MeMBT) to sulfidize the surface of inorganic perovskites. On the one hand, the robust Pb–S bond effectively passivates the under-coordinated Pb²⁺ ions and mitigates non-radiative recombination at the surface. On the other hand, 2-MeMBT molecules exhibit slight penetration into the film, facilitating a suitable arrangement of the energy level near the surface. This configuration reduces the energy barrier for carrier transport in inverted devices and enhances both carrier extraction and transport efficiency. The power conversion efficiency (PCE) of the IPSCs treated with the aforementioned NSSR strategy has reached 21.21%, marking it as one of the highest PCE values currently recorded for IPSCs.