Multilayer Graphene Control of Energy- and Momentum-Selective Near-Field Radiative Heat Transfer for Thermoradiative Energy Conversion

Near-field radiative heat transfer provides a means of enhancing photon exchange across nanoscale vacuum gaps, but its spectral and momentum distributions are strongly constrained by the electromagnetic properties of the interacting materials. Here, we investigate multilayer graphene as an actively tunable means of controlling near-field radiative heat transfer in an InSb-hBN thermoradiative device. Twelve configurations with independently tunable graphene layers on the inner and outer surfaces of the InSb emitter and hBN receiver are systematically analyzed using fluctuational electrodynamics for anisotropic stratified media coupled with detailed-balance semiconductor transport, including Auger and Shockley-Read-Hall recombination. Energy- and momentum-resolved transmission analysis reveals distinct functions of the graphene layers. The sheets adjacent to the vacuum gap establish the dominant high-k∥ photon-transfer channels, whereas the outer layers modify the spectral balance between useful above-bandgap and parasitic sub-bandgap transport. At a 10 nm vacuum gap, the fully graphene-clad [G-InSb-G]-[G-hBN-G] configuration achieves a power density of 44.29 W cm−2, compared with 0.678 W cm−2 for the graphene-free reference, corresponding to an approximately 65-fold enhancement. Adaptive optimization of the graphene chemical potentials maintains approximately 10 W cm⁻² power density and 18% conversion efficiency at a 60 nm gap, where the reference device becomes ineffective under nonradiative recombination losses. Increasing the hBN thickness from 5 to 20 nm, with the chemical potentials re-optimized, further raises the power density to 89.98 W cm⁻² and the efficiency to 28.46% at a 10 nm gap. The results establish multilayer graphene as an actively tunable platform for controlling energy- and momentum-resolved near-field radiative heat transfer and its conversion into electrical power.