Optical and electrical properties of single-crystalline zirconium carbide

Performance enhancement of near-field thermoradiative devices using hyperbolic metamaterials

We analyze a near-field thermoradiative device that consists of an indium arsenide-based photodiode under negative illumination. We analyze a possible enhancement of conversion efficiency by use of hyperbolic metamaterial (HMM) in place of bulk metallic heat sink. A stack of alternating thin-films of metal [zirconium carbide (ZrC)] and dielectric [silicon dioxide (SiO₂)] is chosen to be the HMM under investigation. The presence of hyperbolic modes creates additional channels of near-field radiative transfer. An increased power density is predicted without a compromise in system efficiency.

'Squeezing' near-field thermal emission for ultra-efficient high-power thermophotovoltaic conversion

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.