Electronic Structure and Optical Properties of α-CH3NH3PbBr3 Perovskite Single Crystal

The electronic structure and related optical properties of an emerging thin-film photovoltaic material CH3NH3PbBr3 are studied. A block-shaped alpha-phase CH3NH3PbBr3 single crystal with the natural < 100 > surface is synthesized solvothermally. The room-temperature dielectric function epsilon = epsilon(1) + i epsilon(2) spectrum of CH3NH3PbBr3 is determined by spectroscopic ellipsometry from 0.73 to 6.45 eV. Data are modeled with a series of Tauc-Lorentz oscillators, which show the absorption edge with a strong excitonic transition at similar to 2.3 eV and several above-bandgap optical structures associated with the electronic interband transitions. The energy band structure and epsilon data of CH3NH3PbBr3 for the CH3NH3+ molecules oriented in the < 111 > and < 100 > directions are obtained from first-principles calculations. The overall shape of epsilon data shows a qualitatively good agreement with experimental results. Electronic origins of major optical structures are discussed.