Metal-semiconductor transition in thin film MAPbI3 perovskite

The structural and electronic properties of the methylammonium lead iodide (MAPbI3, MA = CH3NH3) perovskite are investigated as a function of temperature by transport measurements, in situ x-ray diffraction, and optical emission. Lowering the temperature, a transition from the tetragonal to the orthorhombic phase takes place, around 160 K. Such structural transition, monitored by temperature-dependent in situ x-ray diffraction and optical emission, is followed by an inversion of the temperature dependence of the electrical resistivity from a semiconductor-like dependence to a metal-like one. The temperature for such semiconductor-metal transition, depending both on the applied electric field and on the optical excitation, is always below the phase transition temperature. The results demonstrate that perovskite materials display interesting scenarios in which lattice structural transitions combined with optical or electrical excitation strongly affect transport properties. The consequences of these characteristics are analyzed in fundamental and applied science perspectives.