Facile Ethylvanillin Passivation for High-Performance CsFA Perovskite Solar Cells in Variable Lighting Environments

Abstract

Carbon-based hybrid halide perovskite solar cells (C-PSCs) have emerged as one of the most attractive photovoltaics due to their exceptional performance and cost-effectiveness. However, defects in the perovskite photoactive layer, particularly undercoordinated Pb²⁺and halide migration, lead to nonradiative recombination, limiting efficiency and stability. Herein, a simple, low-temperature, and cost-effective surface passivation method was employed to mitigate defects in the CsFA-based perovskite surface with 3-ethoxy-4-hydroxybenzaldehye (ethylvanillin: EVL). The –CHO and –OH groups in EVL effectively passivate Pb²⁺defects and suppress I^–migration, as confirmed by X-ray photoelectron spectroscopy (XPS) and full-range infrared analysis, including mid-infrared region and far-infrared region FIR. This passivation significantly enhances the power conversion efficiency (PCE) of C-PSCs by 9.4% (13.03% to 14.26%) with Spiro-OMeTAD and 11.1% (10.14% to 11.26%) with CuSCN as a hole transporting layer (HTL) under 1 sun illumination and 0.09 cm²active area. Notably, CuSCN demonstrates a superior hole extraction with 4.1% V<inf>oc</inf>and 6.5% fill factor gains. Furthermore, unencapsulated C-PSCs with Spiro-OMeTAD devices retain ∼91% of their initial PCE after 2160 h under the ISOS-D-1 protocol and 86% after 80 min under an ISOS-L-1 protocol, demonstrating exceptional stability and reproducibility with EVL at 7.5 mg/mL. Under low-intensity LED illumination (simulating indoor environments), EVL-passivated C-PSCs with Spiro-OMeTAD achieve remarkable PCEs of 28.12%, 28.05%, and 30.65% at 1000, 500, and 200 lx, respectively. These results highlight EVL-passivated C-PSCs as a cost-effective, stable, and high-efficiency solution for both outdoor and indoor photovoltaic applications.