The preparation of carbon-based hole-free transport layer all-inorganic perovskite CsPbI₂Br solar cells is straightforward, cost-effective, and currently one of the key research areas. However, the interface between the CsPbI₂Br perovskite layer, fabricated via one-step solution spin-coating, and the carbon electrode is characterized by a high density of defects. These defects contribute to substantial non-radiative recombination, which severely limits the device’s photoconversion efficiency. To address this issue, we present an exceptionally simple interface modification strategy aimed at enhancing the interface quality between the CsPbI₂Br perovskite layer and the carbon electrode. Specifically, we introduce 2-aminobenzothiazole (BTA) as an interface modifier. By spin-coating an isopropanol solution containing various concentrations of BTA onto the surface of the CsPbI₂Br perovskite layer, we passivate the surface defects, thereby improving the interface quality and boosting both device performance and operational stability. The thiazole ring and amino group in BTA effectively reduce the defect density on the CsPbI₂Br perovskite surface through Lewis acid-base coordination. This modification substantially improves both the surface morphology and the interface contact of the CsPbI₂Br perovskite film, leading to an enhanced internal electric field and a reduction in non-radiative recombination. Furthermore, the inherent dipole moment of BTA molecules generates an electric dipole layer at the CsPbI₂Br interface, which modulates the electronic states and work function at the interface, optimizing the energy level alignment between the perovskite layer and the carbon electrode. As a result, the interface characteristics between the CsPbI₂Br perovskite film and the carbon electrode are effectively tuned, facilitating improved hole extraction and transport. Consequently, the device incorporating BTA treatment exhibits a photoelectric conversion efficiency (PCE) of 14.17%, an open-circuit voltage (V_OC) of 1.25 V, a short-circuit current density (J_SC) of 14.62 mA cm⁻², and a fill factor (FF) of 77.61%. These values are significantly higher compared to those of devices without BTA treatment (PCE: 12.40%, V_OC: 1.21 V, J_SC: 14.19 mA cm⁻², FF: 72.23%). Furthermore, after 30 days of exposure to air at 20% relative humidity, the BTA-treated device retains 80% of its initial efficiency, whereas the untreated device only maintains 50% of its initial efficiency. This demonstrates that the BTA-modified device offers remarkable reproducibility and environmental stability. The proposed BTA interface modification strategy provides valuable insights for the development of efficient and stable carbon-based hole-free transport layer all-inorganic CsPbI₂Br perovskite solar cells.

Key words: all-inorganic perovskite, CsPbI₂Br, defect passivation, interface modification, dipole molecule