Micron-sized liquid nitrogen-cooled indium antimonide photovoltaic cell for near-field thermophotovoltaics

Electrodeposition of Indium from an Ionic Liquid Investigated by In Situ Electrochemical XPS

The electrochemical behavior and electrodeposition of indium in an electrolyte composed of 0.1 mol/L InCl3 in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py1,4]TFSI) on a gold electrode were investigated. The cyclic voltammogram revealed several reduction and oxidation peaks, indicating a complex electrochemical behavior. In the cathodic regime, with the formation of an In-Au alloy, the reduction of In(III) to In(I) and of In(I) to In(0) takes place. In situ electrochemical X-ray photoelectron spectroscopy (XPS) was employed to investigate the reduction process by monitoring the oxidation states of the components during the cathodic polarization of 0.1 mol/L InCl3/[Py1,4]TFSI on a gold working electrode under ultra-high vacuum (UHV) conditions. The core electron binding energies of the IL components (C 1s, O 1s, F 1s, N 1s, and S 2p) shift almost linearly to more negative values as a function of the applied cell voltage. At −2.0 V versus Pt-quasi reference, In(I) was identified as the intermediate species during the reduction process. In the anodic regime, a strong increase in the pressure in the XPS chamber was recorded at a cell voltage of more than −0.5 V versus Pt quasi reference, which indicated, in addition to the oxidation reactions of In species, that the oxidation of Cl− occurs. Ex situ XPS and XRD results revealed the formation of metallic In and of an In-Au alloy.

A Review on Thermophotovoltaic Cell and Its Applications in Energy Conversion: Issues and Recommendations

Generally, waste heat is redundantly released into the surrounding by anthropogenic activities without strategized planning. Consequently, urban heat islands and global warming chronically increases over time. Thermophotovoltaic (TPV) systems can be potentially deployed to harvest waste heat and recuperate energy to tackle this global issue with supplementary generation of electrical energy. This paper presents a critical review on two dominant types of semiconductor materials, namely gallium antimonide (GaSb) and indium gallium arsenide (InGaAs), as the potential candidates for TPV cells. The advantages and drawbacks of non-epitaxy and epitaxy growth methods are well-discussed based on different semiconductor materials. In addition, this paper critically examines and summarizes the electrical cell performance of TPV cells made of GaSb, InGaAs and other narrow bandgap semiconductor materials. The cell conversion efficiency improvement in terms of structural design and architectural optimization are also comprehensively analyzed and discussed. Lastly, the practical applications, current issues and challenges of TPV cells are critically reviewed and concluded with recommendations for future research. The highlighted insights of this review will contribute to the increase in effort towards development of future TPV systems with improved cell conversion efficiency.

Near-Field Thermophotovoltaic Conversion with High Electrical Power Density and Cell Efficiency above 14

A huge amount of thermal energy is available close to material surfaces in radiative and nonradiative states, which can be useful for matter characterization or energy harvesting. Even though a full class of novel nanoengineered devices has been predicted over the last two decades for exploiting near-field thermal photons, efficient near-field thermophotovoltaic conversion could not be achieved experimentally until now. Here, we realize a proof of principle by using a micrometer-sized indium antimonide photovoltaic cell cooled at 77 K and approached at nanometer distances from a hot (∼730 K) graphite microsphere emitter. We demonstrate a near-field power conversion efficiency of the cell above 14% and unprecedented electrical power density outputs (0.75 W cm^-2), which are orders of magnitude larger than all previous attempts. These results highlight that near-field thermophotovoltaic converters are now competing with other thermal-to-electrical conversion devices and also pave the way for efficient photoelectric detection of near-field thermal photons.

New insights into the thermal behavior and management of thermophotovoltaic systems

The thermal behavior of a thermophotovoltaic system composed of a metallo-dielectric spectrally selective radiator at high temperature and a GaSb photovoltaic cell in the far field is investigated. Using a coupled radiative, electrical and thermal model, we highlight that, without a large conductive-convective heat transfer coefficient applied to the cell, the rise in temperature of the photovoltaic cell induces dramatic efficiency losses. We then investigate solutions to mitigate thermal effects, such as radiative cooling or the decrease of the emissivity or the temperature of the radiator. Without extending the radiating area beyond that of the cell, gains by radiative cooling are marginal. However, for a given radiator temperature, decreasing its emissivity is beneficial to conversion efficiency and, in cases of limited conductive-convective cooling capacities, even leads to larger electrical power outputs. More importantly, for a realistic radiator structure made of tungsten and hafnium oxide, larger conversion efficiencies are reached with smaller radiator temperatures because thermal losses and thus needs for cooling are less.

Harvesting the Electromagnetic Energy Confined Close to a Hot Body

In the close vicinity of a hot body, at distances smaller than the thermal wavelength, a high electromagnetic energy density exists due to the presence of evanescent fields radiated by the partial charges in thermal motion around its surface. This energy density can surpass the energy density in vacuum by several orders of magnitude. By approaching a photovoltaic (PV) cell with a band gap in the infrared frequency range, this nonradiative energy can be transferred to it by photon tunnelling and surface mode coupling. Here we review the basic ideas and recent progress in near-field energy harvesting.