Fast electronic trapping and de-trapping by mid-gap states in CH3NH3PbCl3 single crystal

The assumed existence of mid-gap states and their roles acting as electronic traps in lead halide perovskites are under intensive discussion. Yet, knowledge about their physical characteristics remains limited due to the lack of directly accessed optical evidence. Here, we report direct access of spectroscopic responses by mid-gap states in one prototypical metal halide perovskite, CH3NH3PbCl3 single crystal. Mid-gap electronic trapping shown by sub-gap absorption and photoluminescence quenching is demonstrated. Quenching of the inter-band photoluminescence leads to instantaneous broadening in the energetic distributions of the mid-gap, making it hard to determine the energy of each individual mid-gap state. Therefore, the subsequent mid-gap luminescence following electronic de-trapping shows largely increased spectral linewidth and varied luminescence maxima energy. Time-resolved photoluminescence revealed the fast trapping and de-trapping kinetics by mid-gap states in the CH3NH3PbCl3 single crystal. By combining existing knowledge about mid-gap states in semiconductor crystals, we define a general on-lattice surface dangling bonds scenario serving as the creation of mid-gap states in the robust CH3NH3PbCl3 single crystal.