Interband and Surface-Influenced Photophysical Processes in CH3NH3PbBr3 Perovskites
Metal halide perovskites (MHPs) are attracting ever-growing interest across diverse optoelectronic subdisciplines. Yet, the physical mechanism underlying photoexcitation and subsequent photocarrier dynamics remains poorly understood, due to the apparent spectroscopic diversities observed for any certain MHP. Here, diverse spectroscopic characteristics, including static spectral line-shapes and time-resolved photoluminescence (TRPL) traces shown by polycrystalline versus single-crystalline CH 3 NH 3 PbBr 3 perovskites, are restudied. Key photophysical merits, including exciton binding energy ( E B ), Sommerfeld factor ( ξ ), and Urbach energy ( E U ) that account for the diversities, are discussed within the established framework of semiconductor optics. The value of ξ , which increases with E B , determines how much the interband absorption is enhanced beyond that expected for free carriers. The intrinsic band-edge luminescence is identified, with its asymmetric spectral line-shape linked to E U via the van Roosbroeck–Shockley relation. Excited phase evolution, accompanied by rapid electron–hole (e–h) pairs dissociation and subsequent occurrence of e–h plasma, is indicated by the two-stage TRPL traces that are only observable for high-quality single crystals. With all the spectroscopic analysis and interpretations rooted in the established semiconductor optical theorems, the mechanistic merits revealed in this study are informative for plausible identification between the interband and excitonic photophysical processes of MHPs.
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