Electronegativity explanation on the efficiency-enhancing mechanism of the hybrid inorganic-organic perovskite ABX₃ from first-principles study

Organic-inorganic hybrid perovskites play an important role in improving the efficiency of solid-state dye-sensitized solar cells. In this paper, we systematically explore the efficiency-enhancing mechanism of ABX₃ (A =CH₃NH₃; B = Sn, Pb; X = Cl, Br, I) and provide the best absorber among ABX₃ when the organic framework A is CH₃NH₃ by first-principles calculations. The results reveal that the valence band maximum (VBM) of the ABX₃ is mainly composed of anion X p states and that conduction band minimum (CBM) of the ABX₃ is primarily composed of cation B p states. The bandgap of the ABX₃ decreases and the absorptive capacities of different wavelengths of light expand when reducing the size of the organic framework A, changing the B atom from Pb to Sn, and changing the X atom from Cl to Br to I. Finally, based on our calculations, it is discovered that CH₃NH₃SnI₃ has the best optical properties and its light-adsorption range is the widest among all the ABX₃ compounds when A is CH₃NH₃. All these results indicate that the electronegativity difference between X and B plays a fundamental role in changing the energy gap and optical properties among ABX₃ compounds when A remains the same and that CH₃NH₃SnI₃ is a promising perovskite absorber in the high efficiency solar batteries among all the CH₃NH₃BX₃ compounds.