Abstract
We numerically demonstrate near-field planar ThermoPhotoVoltaic systems with very high efficiency and output power, at large vacuum gaps. Example performances include: at 1200 °K emitter temperature, output power density 2 W/cm2 with ~47% efficiency at 300 nm vacuum gap; at 2100 °K, 24 W/cm2 with ~57% efficiency at 200 nm gap; and, at 3000 °K, 115 W/cm2 with ~61% efficiency at 140 nm gap. Key to this striking performance is a novel photonic design forcing the emitter and cell single modes to cros resonantly couple and impedance-match just above the semiconductor bandgap, creating there a ‘squeezed’ narrowband near-field emission spectrum. Specifically, we employ surface-plasmon-polariton thermal emitters and silver-backed semiconductor-thin-film photovoltaic cells. The emitter planar plasmonic nature allows for high-power and stable high-temperature operation. Our simulations include modeling of free-carrier absorption in both cell electrodes and temperature dependence of the emitter properties. At high temperatures, the efficiency enhancement via resonant mode cross-coupling and matching can be extended to even higher power, by appropriately patterning the silver back electrode to enforce also an absorber effective surface-plasmon-polariton mode. Our proposed designs can therefore lead the way for mass-producible and low-cost ThermoPhotoVoltaic micro-generators and solar cells.
Highlights
We numerically demonstrate near-field planar ThermoPhotoVoltaic systems with very high efficiency and output power, at large vacuum gaps
The currently most developed TPV systems use the emitter far-field radiation to transfer thermal energy across a mm-scale vacuum gap to the PV cell, so their output power density is limited by the blackbody radiation limit
We propose a planar TPV system and a key design method to accomplish ‘squeezed’ narrowband near-field thermal-power transmission, with record-high heat-to-electricity efficiencies, at variably-high power levels, from low up to extremely-high emitter temperatures, with realistic material parameters and a large vacuum gap
Summary
We numerically demonstrate near-field planar ThermoPhotoVoltaic systems with very high efficiency and output power, at large vacuum gaps. Example performances include: at 1200 °K emitter temperature, output power density 2 W/cm[2] with ~47% efficiency at 300 nm vacuum gap; at 2100 °K, 24 W/cm[2] with ~57% efficiency at 200 nm gap; and, at 3000 °K, 115 W/cm[2] with ~61% efficiency at 140 nm gap Key to this striking performance is a novel photonic design forcing the emitter and cell single modes to cros resonantly couple and impedance-match just above the semiconductor bandgap, creating there a ‘squeezed’ narrowband near-field emission spectrum. ThermoPhotoVoltaics (TPV)[1,2,3,4] is a heat-to-electricity conversion mechanism, wherein Thermal radiation is absorbed by a semiconductor PhotoVoltaic (PV) cell It is very favorable, as it involves no moving parts, allowing the possibility for compact, light ( portable), quiet and long-lived generators, powerable from numerous sources, such as high-energy-density hydrocarbon[5] or nuclear[6] fuels, or solar irradiation[7,8,9]. Semiconductor emitters are limited by their relatively low melting temperatures and their bandgap shift and smearing at high temperatures[32]
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