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Understanding the origin of broad-band emission in CH3NH3PbBr3

Broad-band emissions related to self-trapped excitons (STEs) in the sub-bandgap region in organic–inorganic hybrid perovskites and double perovskite crystals have drawn attention in recent times due to their potential in optoelectronic device applications. In this study, we have shown that the formation of STEs in CH3NH3PbBr3 single crystals can be controlled using a suitable sample synthesis procedure. We have observed a broad-band emission (FWHM ∼ 80 nm) for crystals whose crystallization is fast, whereas it was absent if we follow slow crystallization procedures. Using UV-Visible absorption spectroscopy, temperature-dependent photoluminescence (PL), time-resolved PL (TRPL), and dc magnetization studies, we concluded that defect-assisted extrinsic self-trapping is dominant here over the intrinsic self-trapping process and excess Pb atoms in interstitial positions are predominantly responsible for the extrinsic self-trapping process.