Optical bandgap energy of CH3NH3PbI3 perovskite studied by photoconductivity and reflectance spectroscopy

Organic-inorganic hybrid perovskite materials have been receiving considerable attention due to their promising applications in many optoelectronic fields. However, the optical bandgap of CH3NH3PbI3 perovskite is still disputed. In order to comprehend the intrinsic characteristics of these materials, we study the near-band-edge optical responses of the solution-processed CH3NH3PbI3 perovskite crystals by photoconductivity and reflectance spectroscopy at room temperature. All these spectra of the CH3NH3PbI3 polycrystals show only one significant absorption edge at 1.58 eV. However, we observe an extra absorption edge at 1.47 eV in CH3NH3PbI3 single crystal. We establish a simple kinetic model of charge annihilation processes to explain why the low-energy structure of the photoconductivity and diffuse reflectance spectra of CH3NH3PbI3 polyerystals disappear, which provides another possibility for understanding the difference in absorption edge. It is noteworthy that this low-energy absorption edge of CH3NH3PbI3 single crystal has, to the best of our knowledge, seldom been reported on organic-inorganic hybrid perovskites. Therefore, the CH3NH3PbI3 single crystal exhibits a relatively wide absorption which makes it a promising candidate for photoelectric applications.