Bandgap Engineering and Enhancing Optoelectronic Performance of a Lead-Free Double Perovskite Cs2AgBiBr6 Solar Cell via Al Doping

In this study, solar cells based on pure Cs2AgBiBr6 and Al-doped metal were fabricated using the sol–gel spin-coating technique. X-ray diffraction (XRD) analysis confirmed the formation of cubic-structured films for both pure and Al-doped. Notably, the grain size of Al-doped Cs2AgBiBr6 was observed to be larger than that of its pure counterpart. The optical properties of these films were investigated using UV–vis spectroscopy, revealing essential parameters such as the bandgap energy (Eg), refractive index (n), extinction coefficients (k), and dielectric constant. While the pure film exhibited an Eg of 1.91 eV, the Al-doped film demonstrated a slightly lower Eg of 1.82 eV. Utilization of these films in solar cell fabrication yielded intriguing results. The J–V curve shows that the pure solar cell displayed a short-circuit current density (Jsc) of 5.01 mA/cm2, a fill factor (FF) of 0.67, an open-circuit voltage (Voc) of 0.89 V, and an efficiency of 3.02%. Al doping led to improvements, with an increase in Voc to 0.91 V, FF to 0.71, and Jsc to 5.29 mA/cm2. Consequently, the overall efficiency surged to 3.40%, marking a substantial 12.5% enhancement compared with the pure solar cell. These findings underscore the efficacy of Al doping in enhancing the performance of Cs2AgBiBr6-based solar cells.