Improving the performance of mixed halide perovskite solar cells through crystal engineering and the alignment of energy band edges

Abstract

The quest for energy-efficient mixed-halide perovskite solar cells focuses on improving device performance by aligning the conduction band (CB) edges of perovskites with the CB of the electron transport layer (ETL) and valence band (VB) edges with the VB of the hole transport layer (HTL). X-ray diffraction (XRD) analysis confirmed the cubic structure of CsPbIBr₂, with the incorporation of MAPbBr₃ improving crystallinity and increasing the crystallite size from 30.6 nm to 35.1 nm. UV-visible spectroscopy revealed a reduction in the optical band gap (E_g) from 2.19 eV to 2.17 eV, leading to enhanced light absorption. Optical parameter analysis indicated an improved refractive index, extinction coefficient, and dielectric constant of the modified film. Current density–voltage (J–V) characterization demonstrated significant improvement in power conversion efficiency (PCE) from 7.37% to 8.13%, which was attributed to improved charge carrier extraction and reduced recombination within the modified film-based device. Improved light harvesting and charge carrier dynamics were confirmed by the red-shifted IPCE and increased efficiency of the modified perovskite-based device. Electrochemical impedance spectroscopy (EIS) analysis confirmed these improvements, showing an increase in recombination resistance (R_rec) from 4549.4 Ω to 4766.1 Ω and a decrease in transfer resistance (R_tr) from 96.7 Ω to 44.3 Ω. These improvements validate the effectiveness of MAPbBr₃ modification in CsPbIBr₂ to achieve high-performance perovskite devices.