Integrated near-field thermo-photovoltaics for on-demand heat recycling

Abstract

The energy transferred via thermal radiation between two surfaces separated by nanometers distances (near-field) can be much larger than the blackbody limit. However, realizing a reconfigurable platform that utilizes this energy exchange mechanism to generate electricity in industrial and space applications on-demand, remains a challenge. The challenge lies in designing a platform that can separate two surfaces by a small and tunable gap while simultaneously maintaining a large temperature differential. Here, we present a fully integrated, reconfigurable and scalable platform operating in near-field regime that performs controlled heat extraction and energy recycling. Our platform relies on an integrated nano-electromechanical system (NEMS) that enables precise positioning of a large area thermal emitter within nanometers distances from a room-temperature germanium photodetector to form a thermo-photovoltaic (TPV) cell. We show over an order of magnitude higher power generation ${\mathrm{P}}_{\mathrm{gen}}\sim 1.25\hat{\mathrm{I}}¼\mathrm{W}\cdot \mathrm{c}{\mathrm{m}}^{-2}$ from our TPV cell by tuning the gap between a hot emitter (${\mathrm{T}}_{\mathrm{E}}\sim 880\mathrm{K}$) and the cold photodetector (${\mathrm{T}}_{\mathrm{D}}\sim 300\mathrm{K}$) from $\sim 500\mathrm{nm}$ to $\sim 100\mathrm{nm}$. The significant enhancement in ${\mathrm{P}}_{\mathrm{gen}}$ at such small distances is a clear indication of near-field heat transfer effect. Our electrostatically controlled NEMS switch consumes negligible tuning power (${\mathrm{P}}_{\mathrm{gen}}/{\mathrm{P}}_{\mathrm{NEMS}}\sim 10^4$) and relies on conventional silicon-based process technologies.