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.

Rapid depletion of fossil fuels due to the growing demand for energy has resulted in a worldwide concern to improve energy conversion efficiency. Yet, the energy conversion of conventional fossil fuel power generation plants remains relatively low (less than 40%) and a huge amount of energy is wasted in the form of heat, leading to global warming issues. Recycling and recuperating even a small portion of energy losses could provide a huge impact on energy saving and minimize the reliance on fossil fuels. Thermophotovoltaic system appears to be a potential candidate to capture, recover, and convert waste heat energy into useful electricity. This paper presents an overview of the recent development of thermophotovoltaic technology for waste heat recovery applications. Each component in the thermophotovoltaic system including thermophotovoltaic generator/heat source, thermal emitter, spectral filter and thermophotovoltaic cells is vital and can be engineered to achieve a better heat-to-electricity conversion efficiency. Recently, researchers have shown great interest in near-field thermophotovoltaic systems where higher power intensity can be captured by the thermophotovoltaic cell, thus improving the overall system performance. Furthermore, the potential locations for energy scavenging in thermal power plants is investigated based on the on-site temperature measurement. In Malaysia, it is estimated that around 3,831 GWh of waste heat energy could be saved in operational thermal power plants. This review will contribute to the knowledge for future development thermophotovoltaic systems in waste heat recovery applications while summarizing the potential locations for energy scavenging in thermal power plants.

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The optimization of thermophotovoltaic (TPV) cell efficiency is essential since it leads to a significant increase in the output power. Typically, the optimization of In0.53Ga0.47As TPV cell has been limited to single variable such as the emitter thickness, while the effects of the variation in other design variables are assumed to be negligible. The reported efficiencies of In0.53Ga0.47As TPV cell mostly remain < 15%. Therefore, this work develops a multi-variable or multi-dimensional optimization of In0.53Ga0.47As TPV cell using the real coded genetic algorithm (RCGA) at various radiation temperatures. RCGA was developed using Visual Basic and it was hybridized with Silvaco TCAD for the electrical characteristics simulation. Under radiation temperatures from 800 to 2000 K, the optimized In0.53Ga0.47As TPV cell efficiency increases by an average percentage of 11.86% (from 8.5 to 20.35%) as compared to the non-optimized structure. It was found that the incorporation of a thicker base layer with the back-barrier layers enhances the separation of charge carriers and increases the collection of photo-generated carriers near the band-edge, producing an optimum output power of 0.55 W/cm2 (cell efficiency of 22.06%, without antireflection coating) at 1400 K radiation spectrum. The results of this work demonstrate the great potential to generate electricity sustainably from industrial waste heat and the multi-dimensional optimization methodology can be adopted to optimize semiconductor devices, such as solar cell, TPV cell and photodetectors.

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The authors gratefully acknowledge the Tenaga Nasional Berhad (TNB) seeding fund (Project code: U-TG-RD-18-04) that is managed by UNITEN R&D Sdn. Bhd. and the BOLD Refresh Publication Fund 2021 (J5100D4103).

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