Improving Solid-State Cooling with Multijunction Design

Stanford University researchers conducted a theoretical analysis of the cooling power density and coefficient of performance in a multi-layered semiconductor system with a double-junction structure composed of gallium arsenide and indium phosphide. The proposed design highlights the potential of solid-state cooling devices and supports progress in their development. The study was published in PRX Energy.

LEDs operate based on the principle of electroluminescence, which involves injecting charge carriers, such as electrons and holes, into a semiconductor. This process alters the semiconductor's electrical properties, enabling it to emit light photons as the charge carriers recombine.

In some cases, the energy required for light emission exceeds the energy within the semiconductor itself. When this happens, heat from the surrounding environment provides the additional energy, allowing the semiconductor to emit light while cooling down.

In this study, researchers proposed using multilayer semiconductors to improve the performance of electroluminescent cooling systems. This approach, known as a multijunction configuration, is already employed in certain advanced photovoltaic solar cells.

The Impact

This study theoretically analyzed the cooling power of electroluminescent cooling systems, finding that performance can be improved by incorporating additional semiconductor layers. The proposed system demonstrates the potential of solid-state cooling devices while providing scientists with a deeper understanding of the underlying physics.

Summary

Electroluminescent cooling operates as the inverse of photovoltaics, where the energy of emitted photons equals the sum of the electrical energy applied to the semiconductor and the heat extracted from its surroundings.

While scientists have recognized that multijunction configurations can improve semiconductor efficiency in photovoltaics, their application to electroluminescent cooling has not been previously explored.

This study conducted a theoretical analysis of cooling power density and coefficient of performance, using a case study involving a double-junction structure composed of gallium arsenide and indium phosphide. Low-pass energy filters were placed between semiconductor layers, each with a distinct band gap.

Each layer emitted photons toward a black body, acting as a hot reservoir, while connecting to a cold reservoir. An external voltage source supplied energy to each semiconductor layer.

The study revealed that combining multiple layers could achieve performance levels unattainable by individual layers. A key finding was that adding more semiconductor layers reduced the operating voltage required for each layer, thereby improving the coefficient of performance at a given cooling power density. 

Funding

The study was supported by the Department of Energy (DOE) Office of Science and by the DOE Photonics at Thermodynamic Limits Energy Frontier Research Center.

Journal Reference:

‌Park, Y., et al. (2024) Multijunction Electroluminescent Cooling. PRX Energy. doi.org/10.1103/prxenergy.3.033002.