Mapping Plasmon-Enhanced Photocurrent in Single Au Nanoplate/MoS2 Heterostructures

Abstract

Two-dimensional MoS₂ is a promising material for applications in energy conversion or light harvesting, but the weak light absorption by monolayer MoS₂ hinders its direct application in devices. To enhance the absorption of MoS₂, various strategies have been developed based on metal–semiconductor heterostructures, where multiple processes can be effective, depending on subtle local nanoscale parameters. Revealing key factors in such processes requires characterization on single heterostructures, at the micro- or even nanoscale. We present direct photocurrent mapping (PCM) on single Au nanoplate/MoS₂ heterostructures inside a photoelectrochemical cell, which reveals intense photocurrent signal at the nanoplate edges. The Au nanoplate/MoS₂/TiO₂ heterostructure exhibits a better performance in comparison to MoS₂/Au nanoplate/TiO₂ structure, achieving maximum photocurrent performance of 32.8 nA under 600 nm excitation wavelength, which represents an enhancement factor of 32× due to the heterostructure. Our PCM measurements indicate that maximum performance is achieved at different excitation wavelengths for varying excitation power, with a transition from a linear power dependence at long excitation wavelengths to superlinear dependence at short excitation wavelengths. A thorough theoretical analysis including both E-field and plasmonic thermal effects revealed different enhancement factors at different excitation wavelengths and powers, in agreement with the experiment. We conclude that the performance of the MoS₂ layer is enhanced by plasmon resonance energy transfer in the spectral range with strong plexcitionic resonance coupling, at longer wavelengths, whereas it is promoted by a thermal effect due to Au interband transitions at shorter wavelengths (<600 nm).