Bandgap reduction and efficiency enhancement in Cs₂AgBiBr₆ double perovskite solar cells through gallium substitution

Lead-free halide double perovskite (LFHDP) Cs₂AgBiBr₆ has emerged as a promising alternative to traditional lead-based perovskites (LBPs), offering notable advantages in terms of chemical stability and non-toxicity. However, the efficiency of Cs₂AgBiBr₆ solar cells faces challenges due to their wide bandgap (E_g). As a viable strategy to settle this problem, we consider optimization of the optical and photovoltaic properties of Cs₂AgBiBr₆ by Gallium (Ga) substitution. The synthesized Cs₂Ag_0.95Ga_0.05BiBr₆ is rigorously characterized by means of X-ray diffraction (XRD), UV-vis spectroscopy, and solar simulator measurements. XRD analysis reveals shifts in peak positions, indicating changes in the crystal lattice due to Ga substitution. The optical analysis demonstrates a reduction in the E_g, leading to improvement of the light absorption within the visible spectrum. Importantly, the Cs₂Ag_0.95Ga_0.05BiBr₆ solar cell exhibits enhanced performance, as evidenced by higher values of open circuit voltage (V_oc), short-circuit current (J_sc), and fill factor (FF), which are 0.94 V, 6.01 mA cm^-2, and 0.80, respectively: this results in an increased power conversion efficiency (PCE) from 3.51% to 4.52%. This research not only helps to overcome film formation challenges, but also enables stable Cs₂Ag_0.95Ga_0.05BiBr₆ to be established as a high-performance material for photovoltaic applications. Overall, our development contributes to the advancement of environmentally friendly solar technologies.