Recently, Professor Qing Zhang and her research team in the Department of Materials Science and Engineering make great progresses on small perovskite-based lasers. The research results are published in international authoritative journals: Advanced Functional Materials (DOI:10.1002/adfm.201601690), Small Methods (DOI: 10.1002/smtd.201700163) and The Journal of Physical Chemistry Letters (DOI: 10.1021/acs.jpclett.7b01857), which was highlighted by Wiley Materials & Views.
Metal halide perovskites have recently attracted great attentions for their breakthrough in solar cell devices. As direct band gap semiconductors, perovskites own large absorption coefficient, tunable bandgap, long carrier diffusion distance and high quantum yield, which also make them excellent candidates for high performance optoelectronic devices including lasers, photodetectors, light emitting diodes, transistors and so on.
Small laser is a kind of coherent light source with physical dimension of one or several light wavelength. Small lasers are central for optical chips and also hold great potentials in ultrahigh-resolution bioimaging and high density data storage. Recently, Professor Zhang’s group used chemical vapor deposition methods to synthesize inorganic single crystalline perovskite nanoplatelets CsPbX3(X=Cl, Br, I) with high optical quality and stability, and further proved that room temperature, tunable high quality laser covers entire visible regime (High-Quality Whispering-Gallery-Mode Lasing from Cesium Lead Halide Perovskite Nanoplatelets). The lasing threshold is 2.2 mJ/cm2, which is lower than most of similar small lasers. The full width at half maxium of lasing mode is 0.14 nm, which is highest comparing with previous similar semiconductor small lasers.
Fig.1 (a) Small perovskite-based lasers. (b) Room temperature Tunable high-quality small whispering-gallery-mode laser based on CsPbX3 single crystals.
Based on in-depth study of perovskite micro-laser, Professor Zhang was invited to write the latest review article of perovskite small laser and its applications in the field of optoelectronic devices (Advances in Perovskite-Based Small Lasers, Small Methods, DOI: 10.1002/smtd.201700163). In this review, the characteristics of perovskite micro-laser are discussed in four aspects: crystal structure, electron structure and band gap engineering, exciton and spontaneous radiation and optical gain. Besides, perovskite materials at different dimension, i.e. films, nanowires and quantum dot, were discussed to evaluate the influence to optical property of perovskite laser. Eventually, the urgent issues for perovskite micro laser and practicable solutions are discussed to pave the way for the development of perovskite small lasers.
Fig.2. Transient absorption spectra for spin-coated quasi-2D perovskite films (n = 3(a, b, c) and n = 5(d, e, f)).
Zhang’s group used transient absorption spectroscopy and photoluminescence spectroscopy to explore structure engineered carrier dynamics in quasi two-dimensional perovskite (PEA)2(MA)n-1PbnI3n+1 (Unveiling Structure Engineered Carrier Dynamics in Hybrid Quasi-Two-Dimensional Perovskites Thin Film Towards Controllable Emission). They found that the multiple phases of perovskites are arranged perpendicularly to substrate from small to large n, and also co-exist randomly in the same horizontal planes. A carrier self-separation dynamics was proven that electrons transfer from small-n to large-n perovskite phases and holes transfer reversely. These results can help applications of two-dimensional layered perovskite films in solar energy conversion and photoelectric detection devices.