Professor Ji‑Hun Lim of Jeonbuk National University (JBNU)(Department of Semiconductor Science and Technology) has analyzed the performance and cost‑effectiveness of thermophotovoltaic cells, which can produce higher power per unit area than conventional solar cells, and proposed criteria for selecting semiconductor materials suitable for waste‑heat recovery and thermal energy storage, along with a system design roadmap.

These research results were published in the international journal in the field of energy conversion ‘Energy Conversion and Management’ (IF=11.8, top 1.9%), in a paper titled ‘Optimizing III-V thermophotovoltaic bandgaps for cost-effective thermal energy conversion’.

Thermophotovoltaic cells (Thermophotovoltaic cell, TPV) are a technology that directly converts radiation emitted from high‑temperature heat sources into electricity using semiconductor devices. They can utilize industrial waste heat, the heat of high‑temperature reactors, and concentrated solar thermal energy, and can be coupled with latent heat storage systems using phase‑change materials or with thermal batteries that store electricity as heat. In particular, by storing excess renewable electricity as heat and reconverting it to electricity when needed, they can help mitigate the intermittency of generation caused by variations in sunlight and wind.

The key technology to improve thermophotovoltaic efficiency is ‘photon recycling’, which returns photons not used for electricity generation back to the heat source. This is achieved by reflecting photons with energy lower than the semiconductor bandgap so they can be reused by the heat source. Even when using very high‑temperature heat sources above 1,000°C, this approach reduces unwanted heat absorption by the device and energy loss, thereby improving conversion efficiency.

Professor Lim conducted opto‑electrothermal integrated analyses that account for optical and resistive losses and device temperature rise for various III-V compound semiconductors with bandgaps ranging from 0.74 eV (InGaAs) to 1.42 eV (GaAs). He evaluated not only conversion efficiency but also the total energy produced during operation and the costs of generation and storage, and showed that the material with the highest efficiency is not necessarily the most advantageous economically.

The analysis found that low‑bandgap materials were limited to a maximum power density of 5 W/cm2 or less due to resistive losses at high current and Joule heating. By contrast, GaAs showed conversion efficiencies above 40% and a maximum power density of 10 W/cm2. This is approximately 400–500 times higher than the power density of solar cells with 20–25% conversion efficiency under standard irradiance of 1,000 W/m2 (0.02–0.025 W/cm2). This indicates that by harnessing the strong radiative energy of a high‑temperature heat source, high power can be produced from a small device area.

Materials that are advantageous from an economic standpoint varied by application. In continuous heat‑supply waste‑heat recovery environments, InGaAs and InGaAsP were found to be favorable, while GaAs was advantageous for thermal energy storage applications that convert stored heat into electricity. On that basis, he presented application‑specific design guidelines that consider not only conversion efficiency and power density but also heat‑source temperature, operating mode, and total energy production.

This study is significant as the first domestic integrated comparison of performance and economics of III-V thermophotovoltaic bandgaps across the two application fields of waste‑heat recovery and thermal energy storage, and for proposing a roadmap for selecting optimal semiconductor materials by application. With related research actively pursued by institutions such as the University of Michigan, MIT, and the National Renewable Energy Laboratory (NREL), this work is expected to broaden the domestic research base that links device development, system design, and economic evaluation.

Professor Lim stated, “Thermophotovoltaic cells are a technology that can recover waste heat into useful electricity, and, when combined with thermal batteries, can help compensate for the intermittency of renewable energy”, adding “To develop this domestically as a next‑generation energy technology, it is important to establish a research base that encompasses semiconductor device development, system design, and economic evaluation”.

He continued “Continuous research support and the cultivation of specialized personnel in related fields are necessary”, and “he expressed hope that this study will serve as the starting point for Korea's independent development and commercialization of thermophotovoltaic technology”.

Meanwhile, this research was carried out with support from the National Research Foundation of Korea(JBNU G‑Lamp Project Group).