A First-Principles Study on ABBr<inf>3</inf> (A = Cs, Rb, K, Na; B = Ge, Sn) Halide Perovskites for Photovoltaic Applications

Perovskite solar cells (PSCs) have received intensive attention and demonstrated power conversion efficiency (PCE) as high as 25.8%. Concerning Pb toxicity and the instability of organic elements, all inorganic lead-free perovskites (ILPs) have been extensively studied to achieve comparable or greater photovoltaic performance. To develop ILPs as an alternative for solar cell (SC) applications, first-principles calculations of ABBr3 perovskites (A = Cs, Rb, K, and Na, and B = Sn, and Ge) is performed. Structural, electronic, and optical properties are systematically studied to probe the potential for photovoltaic applications. These ILPs exhibit a direct bandgap in the range of 1.10–1.97 eV, which is highly beneficial for absorbing solar energy. Furthermore, these ILPs demonstrated significant optical absorption (over 105 cm−1) in the UV–Vis spectrum. These results will help design high-performance lead-free PSCs.