Cooling with electroluminescent semiconductors
Theorists propose a new approach to electroluminescent cooling that works like inverted solar photovoltaic cells.
image: Proposed multijunction electroluminescent cooling system, consisting of multiple semiconductor layers with different band gaps (the energy needed to move an electron so it can conduct electricity).
Credit: Image courtesy of Yubin Park
The Science
Electroluminescence is the phenomenon behind how LEDs work. It involves adding charge carriers, either electrons or holes, to a semiconductor. This changes the semiconductor’s properties, including how it conducts or insulates against the movement of electrical charges. In an LED, the charge carriers cause the semiconductor to emit photons of light. This emission can require more energy than is present in the semiconductor. If this is the case, the excess energy to make light comes from heat around the semiconductor. The result—a semiconductor can cool down by emitting light. In this study, researchers proposed a way to improve the performance of this electroluminescent cooling by using multilayer semiconductors. This approach, called a multijunction configuration, is already used in some special photovoltaic solar cells.
The Impact
This study conducted a theoretical analysis of cooling power in electroluminescent cooling systems. It found that increasing the number of semiconductor layers can improve cooling performance. The proposed cooling system highlights the potential of solid-state cooling devices. This work also improves scientists’ understanding of the physics underlying these systems.
Summary
Electroluminescent cooling is the reverse of photovoltaics. The emitted photon energy equals the amount of electrical energy supplied to the semiconductor plus the removal of heat from the semiconductor’s surroundings. In photovoltaics, scientists know that multijunction configurations can improve semiconductor efficiency. However, researchers have not previously explored multijunction configurations for electroluminescent cooling.
This research conducted a theoretical analysis on cooling power density and coefficient of performance. The research used a case study featuring a double-junction structure with gallium arsenide and indium phosphide semiconductor materials. The system consisted of multiple semiconductor layers with different band gaps and low-pass energy filters placed between the layers. Every semiconductor layer was connected to the cold reservoir and emitted photons toward a black body that served as a hot reservoir. External electrical power was provided by applying a voltage to each semiconductor layer. The research showed that the combination of these layers results in performance levels that are unattainable by using each layer individually. One key discovery was that for a given cooling power density, increasing the number of semiconductor layers can lower the operating voltage of each layer, leading to an improved coefficient of performance.
Funding
This research was funded by the Department of Energy (DOE) Office of Science and by the DOE Photonics at Thermodynamic Limits Energy Frontier Research Center.