Electronegativity explanation on the efficiency-enhancing mechanism of the hybrid inorganic–organic perovskite ABX_3 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 ABX_3（A = CH_3NH_3; B = Sn,Pb; X = Cl, Br, I） and provide the best absorber among ABX_3 when the organic framework A is CH_3NH_3 by first-principles calculations. The results reveal that the valence band maximum（VBM） of the ABX_3 is mainly composed of anion X p states and that conduction band minimum（CBM） of the ABX_3 is primarily composed of cation B p states. The bandgap of the ABX_3 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 CH_3NH_3 Sn I_3has the best optical properties and its light-adsorption range is the widest among all the ABX_3 compounds when A is CH_3NH_3. 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 ABX_3 compounds when A remains the same and that CH_3NH_3 Sn I_3 is a promising perovskite absorber in the high efficiency solar batteries among all the CH_3NH_3BX_3 compounds.