Static And Dynamic Structures Of Perovskite Halides Abx(3) (B = Pb, Sn) And Their Characteristic Semiconducting Properties By A Huckel Analytical Calculation

Solid solutions of methylammonium lead iodide (CH3NH3PbI3, abbreviated as MAPbI(3)) and fonriamidinium lead iodide (CH(NH2)(2)PbI3, as FAPbI(3)), which have been expected to be suitable materials as a visible light absorber of solar cells, were characterized by differential thermal analysis (DTA), XRD, H-1, Pb-267 NMR and I-127 nuclear quadrupole resonance (NQR). Continuous solid solutions of MAPbI(3) and FAPbI(3) were confirmed to have a cubic perovskite structure at 298 K except the tetragonal MAPbI(3). (127)INQR 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 (3) over barm. FAPbI(3) (Black phase) showed similar successive phase transitions at around 120-140 K and 283 K. The motional narrowing phenomenon observed on the Pb-267 NMR proved useful to evaluate the halide ion migration and the activation energies were estimated to be ca. 48 kJ/mol for APbBr(3) (A = Cs and CH3NH3), while the narrowing phenomena could not be observed clearly for MAPbI(3) below 500 K, suggesting a lower concentration of vacancies than bromide analogs. Finally, Huckel calculations were performed for ABX(3) (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.