DOI: https://doi.org/10.29363/nanoge.emlem.2024.037
Publication date: 13th July 2024
Lead halide perovskites of the type APbX3, where Α is an organic/inorganic cation and X a halogen atom, attract wide interest based on their outstanding achievements in the field of photovoltaics. The vast majority of works in the field involve iodine-based perovskites, with an energy gap suitable for solar cell applications. By contrast, relatively few are the works dealing with the wider-gap chlorine-based perovskites emitting in the deep blue-near ultraviolet part of the spectrum.
In this work, we study the lasing process in a vertical-cavity surface-emitting laser structure, containing as active medium 2-10 μm-thick single crystals of MAPbCl3 in between SiO2/Ta2O5 distributed Bragg reflectors [1],[2]. In such a MAPbCl3 vertical cavity, we observe for the first-time dual wavelength lasing at 78 K, occurring at 414 and 391 nm at different thresholds. To understand this complex lasing behaviour, the single crystals were extensively studied in terms of micro-photoluminescence and micro-reflectivity experiments as a function of temperature.
In micro-reflectivity spectra at 78 K, aside from a strong exciton feature, marking the excitonic gap at ~385 nm of the orthorhombic phase of MAPbCl3, we also observe a distinct exciton feature at ~412 nm, next to the second laser line. This second exciton feature, never reported before in any MAPbCl3 system, strongly suggests the coexistence within the orthorhombic lattice of a “second” crystal phase, which is present in ample quantities to be able to give rise to such pronounced reflectivity signature. We show that this second phase persists up to room temperature, well above the orthorhombic-to-cubic transition at 170K, making it very unlikely that it consists of “cubic” inclusions. Our experiments further suggest that this second phase depends on the growth method and crystal size and that is possibly a more general feature of the MAPbCl3 system than originally thought. The conclusions drawn from this study are likely to lead to an enhanced understanding of the MAPbCl3 system and pave the way for new photonic devices in the deep blue-UV region.
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