Na⁺-Intercalated Two-Dimensional Vermiculite-Modified TiO₂ Electron Transport Layer for Enhanced CsPbI₂Br Perovskite...

Interface engineering of the electron transport layer (ETL) is an effective strategy for enhancing the performance and stability of all-inorganic perovskite solar cells (PSCs). Herein, Na⁺-intercalated vermiculite nanosheets were introduced as a low-cost natural interfacial modifier for the TiO₂ ETL in CsPbI₂Br PSCs. The nanosheets were prepared via an aqueous-phase exfoliation process and deposited onto the TiO₂ surface to regulate the buried TiO₂/CsPbI₂Br interface. Morphological and spectroscopic characterizations revealed that vermiculite modification reduced the surface roughness of TiO₂, altered its surface chemical/electronic environment and was associated with improved interfacial energy-level alignment. As a result, the quality of the CsPbI₂Br film was significantly improved, leading to larger grains, enhanced crystallinity, a lower apparent trap-state density, and more efficient interfacial charge-transfer behavior. Electrical characterizations further confirmed enhanced charge extraction, reduced carrier recombination, and an increased built-in potential in the modified devices. Consequently, the vermiculite-modified devices exhibited simultaneous improvements in power conversion efficiency (PCE), open-circuit voltage, and short-circuit current density, with the best-performing device reaching a PCE of 13.94%. In addition, the modified device retained 84.51% of its initial PCE after storage in air for 35 days, significantly higher than the 71.1% retained by the control device. These findings highlight the potential of Na⁺-intercalated vermiculite nanosheets as low-cost natural modifiers for TiO₂/CsPbI₂Br buried-interface engineering in efficient and stable all-inorganic PSCs.