The experimental observation of strong photoluminescence enhancement in a tungsten diselenide (WS2
) monolayer by energy transfer from CsPbBr3
perovskite quantum dots may lead to the development of improved optoelectronic devices based on atomically thin layers of semiconducting transition metal dichalcogenides (TMDCs).
The latter are promising for light-harvesting and light-emitting applications, exhibiting a range of favorable features, including high charge-carrier mobility, a direct optical bandgap (as opposed to their counterparts in bulk or a-few-layer form), and the possibility of mitigating the effect of dielectric screening through their extremely small thickness. However, their low absorption cross sections and photoluminescence quantum yields (PLQYs), which typically characterize semiconductor materials with such small thicknesses, limit their applicability in photonic devices. Now, a collaboration led by Tian Jiang reports a simple route to overcome these difficulties. It relies on hybrid architectures involving the interfacing of WS2
monolayers with CsPbBr3
perovskite quantum dots and capitalizes on the excitonic nature of optical excitations to couple the two constituent materials through efficient nonradiative energy transfer. Colloidal lead halide perovskite semiconductor nanocrystals (MPbX3
, X = Cl, Br, I),
either in their hybrid organic-inorganic form (M = CH3
) or in all-inorganic compositions (M = Cs) are attractive media for solar cells, having enabled efficiencies in excess of 20%. A number of favorable attributes currently draw attention to these materials for the development of microlasers and diode lasers. Interesting properties include their high gain coefficients and ambipolar charge mobility, remarkable photostability, wavelength tunable emission over the entire visible spectrum via compositional variations, and PLQYs up to 90%. In the type I CsPbBr3
heterostructure developed in these experiments, nonradiative energy transfer is exploited to extract carriers generated by the 405-nm laser irradiation in the wide bandgap CsPbBr3
colloidal perovskite nanocrystals and to transfer them with an efficiency and rate of ~40% and ~2×108
, respectively, into the narrow bandgap WS2
monolayer. Notably, the excitonic energy transfer from the nanocrystals through diffusion is greatly facilitated by the inherent property of atomically thin TMDC layers to exhibit reduced dielectric screening. The realization of this hybrid energy transfer scheme enabled a strong enhancement of the photoluminescence intensity of the integrated WS2
layer that was 12.7 times the value obtained from an isolated WS2
monolayer and led to a 4.6-fold increase in its internal quantum efficiency to the level of 29%. The reduced dielectric screening effect in monolayer TMDC materials and the flexibility that it offers in terms of control over the excitonic energy transfer in hybrid material architectures may open up possibilities for the realization of a new generation of optoelectronic devices with enhanced performance.
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