Excitonic behavior in hybrid halide perovskite for optoelectronic applications

Organic-inorganic lead halide perovskites, CH₃NH₃PbX₃ (X=Cl, Br, I), have gained great attentions for their attractive optoelectronic properties and excellent performances in various optoelectronic devices. To resolve the remained issues and advance the optoelectronic application devices, understanding intrinsic properties of this material is significant. In particular, free carrier and excitonic behaviors play a crucial role to support the charge transport process which aids the advanced device design. We verified structural properties using temperature dependence photoluminescence and transmission spectra. Under 160 K as orthorhombic phase, unusual excitonic behaviors were found near band edge. We also determined surface potential distribution with and without external light source using Kelvin probe force microscopy. We described electronic band structures of halide perovskite effected by photovoltage. Since the large band gap energy about 3 eV, different photovoltages characteristics were displayed depending on the wavelength of the light source, and it is affected by the defect states on the band edges and the bound excitons on the band edge. Those results suggest that the identified perovskite structure and excitonic properties will apply to many optoelectronic devices.