Optical bandgap energy of CH 3 NH 3 PbI 3 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 CH 3 NH 3 PbI 3 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 CH 3 NH 3 PbI 3 perovskite crystals by photoconductivity and reflectance spectroscopy at room temperature. All these spectra of the CH 3 NH 3 PbI 3 polycrystals show only one significant absorption edge at 1.58 eV. However, we observe an extra absorption edge at 1.47 eV in CH 3 NH 3 PbI 3 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 CH 3 NH 3 PbI 3 polycrystals disappear, which provides another possibility for understanding the difference in absorption edge. It is noteworthy that this low-energy absorption edge of CH 3 NH 3 PbI 3 single crystal has, to the best of our knowledge, seldom been reported on organic-inorganic hybrid perovskites. Therefore, the CH 3 NH 3 PbI 3 single crystal exhibits a relatively wide absorption which makes it a promising candidate for photoelectric applications.