Static and Dynamic Structures of Perovskite Halides ABX3 (B = Pb, Sn) and Their Characteristic Semiconducting Properties by a Hückel Analytical Calculation

Abstract

Abstract Solid solutions of methylammonium lead iodide (CH3NH3PbI3, abbreviated as MAPbI3) and formamidinium lead iodide (CH(NH2)2PbI3, as FAPbI3), which have been expected to be suitable materials as a visible light absorber of solar cells, were characterized by differential thermal analysis (DTA), XRD, 1H, 207Pb NMR and 127I nuclear quadrupole resonance (NQR). Continuous solid solutions of MAPbI3 and FAPbI3 were confirmed to have a cubic perovskite structure at 298 K except the tetragonal MAPbI3.127I NQR spectra as well as DTA for CH3NH3PbI3 showed successive phase transitions at 162 K and 333 K associated with the space group transformation from Pnma, I4/mcm to Pm$\bar{3}$m. FAPbI3 (Black phase) showed similar successive phase transitions at around 120–140 K and 283 K. The motional narrowing phenomenon observed on the 207Pb NMR proved useful to evaluate the halide ion migration and the activation energies were estimated to be ca. 48 kJ/mol for APbBr3 (A = Cs and CH3NH3), while the narrowing phenomena could not be observed clearly for MAPbI3 below 500 K, suggesting a lower concentration of vacancies than bromide analogs. Finally, Hückel calculations were performed for ABX3 (B = Sn, Pb) to demonstrate their excellent performance as a visible light absorber of solar cells, i.e., the direct band gap transition with a tunable property and the small effective masses of electron and hole.