Design and integration of a versatile thermophotovoltaic sub-system – DIVERSITY

The main objective of the project is to design and fabricate a thermophotovoltaic sub-system (hot body at a temperature comprised between 1000 and 1500 °C – called emitter –, low bandgap [0.5 to 0.6 eV] photovoltaic cells, included within a closed cavity), with record performances (sub-system efficiency significantly larger than 12%) and integrable into various thermophotovoltaic systems.
Sub-objective 1 aims at optimizing heat transfer in the sub-system. Research paths involve specific photonic design of the PV cells, and the optical and thermal design of the cavity, with appropriate selection of geometry, dimensions and materials. Sub-objective 2 aims at optimizing photovoltaic conversion on areas larger than 1 cm². Research paths involve high quality semiconductor mid-infrared absorbers, efficient passivation techniques, thinning the absorber layer, using thick top contacts and/or diluting radiation, and fabricating an array of PV cells. Sub-objective 3 aims at demonstrating high-performance TPV sub-systems. Research paths involve a first demonstration in controlled lab-conditions using a blackbody emitter. The second demonstration consists in integrating the developed TPV sub-system into a solar-TPV system operating in real conditions.
An analysis of the state-of-the-art reveals that there is currently a gap between the record TPV pairwise efficiency (over 40%) and the record TPV system efficiency (11.2%). One possible reason for this gap is the challenge of developing simultaneously high-performance elements (emitter, cavity, TPV cells). The first ambition of the project is to address this challenge. Even though some of the best pairwise efficiencies were achieved with InGaAs TPV cells, using lower-bandgap InGaAsSb TPV cells is more appropriate for emitter temperatures comprised between 1000 and 1500 °C. The second ambition of the project is to design and fabricate InGaAsSb TPV cells, and also modules, with record-breaking performance. Finally, even though there are articles dealing with optimizing the cavity between the emitter and the TPV cells, these articles are quite limited in number and applied to specific configurations. The last ambition of the project is to contribute to meeting the challenge of demonstrating an efficient and versatile TPV sub-system in lab conditions, and by integrating it in a solar-TPV system operating in real solar illumination conditions.
The methodology consists of one coordination and three scientific tasks. The first task will involve photonics simulations for meeting requirements on spectral selectivity, optics simulations for minimizing losses in the cavity, and multi-physics simulations for minimizing all heat losses in the sub-system. The second task will be dedicated to the TPV cells and modules. Opto-electronics simulations will be made for minimizing losses in the TPV cells. Then TPV cells and modules will be fabricated using Molecular Beam Epitaxy, semiconductor device cleanroom processes, and their performances will be assessed using optical and electrical characterization platforms. Photonic components ensuring spectral selectivity will be fabricated using patterning and coating technologies and evaluated using optical characterization platforms. The third task will be dedicated to TPV sub-systems and systems. A TPV sub-system operating in laboratory conditions will be fabricated and characterized. This subsystem will be integrated into a solar-TPV system and its performances will be characterized under concentrated sunlight. A final sub-task will consist in performing environmental footprint and up-scaling analyses.
To implement this research program, an interdisciplinary consortium brings together experts in various fields: photonics and thermophotovoltaics (LAAS-CNRS), III-Sb semiconductor physics and epitaxial growth (IES), multi-physics analysis and instrumentation of PV converters under high-illumination (PROMES).