Graded-index structures for high-efficiency solar thermophotovoltaic emitting surfaces

Abstract

This Letter presents a highly efficient emitter structure for solar thermophotovoltaic systems. The structure consists of a graded index on tungsten, shows a spectral efficiency of 59%, or 70% with the use of a back reflector, and is compared to other state-of-the-art emitter structures. The effects of different structures and periodicities on the efficiency of the emitter are explored, as well as the effect of a protective oxide coating. The causes of the antireflection properties of these structures are also explored.

Design of emitter structures based on resonant perfect absorption for thermophotovoltaic applications

“…While a spectrally narrow emission is desired to reduce thermalization loss in the PV cell, some bandwidth is required to increase the power density of the emitted radiation. Systems with extremely narrow emission require a large emitter area, which results in a large PV cell area requirement and a greatly increased system cost [3][4][5][6].…”

“…As a result, STPV systems have the potential to be far more efficient than PV cells. By controlling the optical properties of the STPV emitting surface, its thermal emission can be spectrally matched to a PV cell, resulting in high efficiency operation [3][4][5][6]. Perhaps the most impressive emitters to date have exploited optical resonances resulting from patterned surfaces, including a VO 2 -based photonic crystal with an optimal spectral efficiency (see Eq.…”

“…(1)) of 54% for InGaSb PV cells with a band gap of 0.62 eV [7], W-based graded index structure with an optimal efficiency of 59% for GaSb PV cells with a band gap of 0.73 eV [5], and W-based photonic crystals with an optimal efficiency of 63% for GaSb PV cells with a band gap of 0.73 eV [8]. However, these structures suffer from several key drawbacks: they typically rely on precise fabrication of sub-wavelength structures to tune their resonant properties, and they require high operating temperatures to achieve high spectral efficiencies.…”

Laser processing of materials for renewable energy applications

“…The authors in Ref. 81 have demonstrated a high effi ciency solar receiver by laser sintering of tungsten nanoparticles on a stainless steel substrate. Through the control of laser processing parameters, the morphology of the sintered nanoparticle layer is governed such that high solar absorptance can be achieved with low thermal emittance.…”

The role of photonics in energy

“…182 Another approach employs a graded-index tungsten emitter structure to enhance the spectral efficiency in the solar TPV system. 183 Future advances will result from the development of materials and the structure design of the emitters, filters, and PV cells to optimize the radiant efficiency and spectral and infra-red photon to electron conversion efficiencies of the PV cells in the TPV systems.…”