Enhanced performance of carbon-based CsPbI2Br perovskite solar cells using interfacial modifiers†

Carbon-based CsPbI₂Br perovskite solar cells (C-PSCs) have attracted significant attention as promising candidates for solar energy conversion due to their optimal bandgap, stability, and ease of fabrication. However, surface and grain boundary defects in CsPbI₂Br contribute to significant non-radiative recombination and energy loss, while the energy level mismatch between the carbon electrode and CsPbI₂Br exacerbates open-circuit voltage (V_oc) loss, limiting photovoltaic performance. To address these challenges, 3-(trifluoromethyl)phenylthiourea (3-TPT) and 4-(trifluoromethyl)phenylthiourea (4-TPT) were introduced as interfacial modifiers. The functional groups in 3-TPT and 4-TPT, including CS, –CF₃, and –NH₂, effectively passivated cationic and anionic defects, reducing defect density and suppressing non-radiative recombination. Additionally, isopropyl alcohol (IPA) solutions of 3-TPT and 4-TPT promoted secondary crystallization and grain reorganization, resulting in larger grains and denser boundaries, which significantly enhanced the CsPbI₂Br crystal quality. Furthermore, 3-TPT and 4-TPT modulated the band structure of CsPbI₂Br, improving the energy level alignment with the carbon electrode and minimizing energy loss. The power conversion efficiencies (PCEs) of C-PSCs modified with 3-TPT and 4-TPT reached 13.78% and 14.15%, respectively, compared to 12.18% for the unmodified device. The –CF₃ groups in 3-TPT and 4-TPT enhanced the hydrophobicity of CsPbI₂Br, effectively mitigating moisture ingress. After 500 h in a humid environment (30% relative humidity), the modified devices retained 81.8% and 85.7% of their initial PCE, significantly outperforming the 50.6% retention of the unmodified device. This study demonstrates a simple and effective approach to improving both the efficiency and long-term stability of carbon-based CsPbI₂Br solar cells.