The photocurrent output of the prototypical photovoltaic CH3NH3PbI3 perovskite strongly depends on the photocarrier generation and dynamics in its optically excited phase. Here we reveal quantitative enhancement in the inter-band continuous absorption beyond free carriers by the Sommerfeld factor in the direct bandgap CH3NH3PbI3 perovskite. High-quality CH3NH3PbI3 single crystal with atomically flat pristine surfaces exhibits doublet photoluminescence as a function of photon energy that is attributable to surface-specific and bulk-dominated luminescence. Exciting power-dependent bulk photoluminescence shows remarkable excitation threshold and optical hysteresis. Bulk photoluminescence decays following a two-stage histogram, i.e., an early stage featured by multi-exponential decaying and a later stage featured by mono-exponential decaying. Taken together, the excitation threshold, the optical hysteresis, and the two-stage time-resolved bulk photoluminescence histogram provide plausible indications of phase evolution and electron-hole droplets nucleation in optically excited room-temperature CH3NH3PbI3 single crystal.
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