DOI: https://doi.org/10.29363/nanoge.almips.2021.022
Publication date: 23rd September 2021
In this study, hyperbolic metamaterials (HMM) are properly designed, simulated and fabricated as an outstanding photonic structure able to control the emission rate of lead halide perovskite nanocrystals (PNCs) deposited on the top. Geometrical parameters (thicknesses of the metal and the dielectrics layer) are optimized to enhance coupling between the HMM and the exciton confined in the PNCs. The device is tested for CsPbI3 PNCs which demonstrate an increase of the exciton radiative recombination rate by more than a factor of 3 together with the 8nm red shift of the emission spectra when the PMMA spacer is 10 nm. The appearance of this redshift exhibits a strong correlation with the coupling of perovskite emitters to the HMM modes. However, the emitter-HMM coupling also produces a decrease of the PL intensity, due to the preferential emission of light into the high-k HMM modes. This negative effect can be overcome by modifying the HMM with diffraction effects or light scattering centers. The second strategy can be easily implemented by simultaneously dispersing onto the HMM/PMMA substrate TiO2 nanospheres together with the perovskite NCs. We saw two distinct beneficial outcomes as a result of this: (i) a significant rise in PL intensity, and (ii) further Purcell enhancement. After deconvolution of the system response, we find that the exciton lifetime is reduced from 0.75 ns (only perovskite NCs) to 0.45 ns (perovskite NCs and TiO2 nanospheres on top of the HMM structure). This results in a Purcell factor increase from 2 (considering here we used a 20 nm PMMA spacer) to greater than 3.3, which is significantly higher than the NC-HMM system's calculated value. This additional Purcell enhancement can be attributed to the Mie resonant effect of the TiO2 nanospheres near the HMM surface. Furthermore, the significant rise in PL intensity in these samples containing TiO2 nanospheres may be attributed to emitter radiative rate enhancement and changes in emission directionality.
Financial support from Spanish MINECO through Project No. TEC2017-86102- C2-1 are gratefully acknowledged. S.G. also acknowledges her “Grisolia” grant from Generalitat 656 Valenciana.
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