Refrigeration is an intrinsic feature of light-emitting diodes, a fact that was recognized decades ago but has so far eluded direct experimental observation at practical power densities. The problem is insufficient external luminescence efficiency; for net cooling to occur, the losses in the device must be close to zero, and a sufficiently efficient LED has yet to materialize. We propose a possible structure for such an LED, and predict that with existing optoelectronic material quality and device processing, electroluminescent refrigeration is not only possible but is potentially more efficient than its solid-state alternatives, particularly at low temperature.
In this work, we first proposed a comprehensive numerical simulation for luminescent coupling efficiency (LCE) in a complete multi-junction (MJ) configuration and discussed its dependencies on temperature, incident light spectrum and bias voltage. We used finite difference time domain (FDTD) method and detailed balance principle to establish an optical transfer model. Based on that, we revealed the predominant influence factors of the simulation results in detail. This work will certainly fill a knowledge gap in understanding LCE and provide guidance to MJ photovoltaic device design and optimization as well.
The new breakthrough in photovoltaics, exemplified by the slogan “A great solar cell has to be a great light-emitting diode (LED)”, has led to all the major new solar cell records, while also leading to extraordinary LED efficiency. As an LED becomes very efficient in converting its electrical input into light, the device cools as it operates because the photons carry away entropy as well as energy. If these photons are absorbed in a photovoltaic (PV) cell, the generated electricity can be used to provide part of the electrical input that drives the LED. Indeed, the LED/PV cell combination forms a new type of heat engine with light as the working fluid. The electroluminescent refrigerator requires only a small amount of external electricity to provide cooling, leading to a high coefficient of performance.
We present the theoretical performance of such a refrigerator, in which the cool side (LED) is radiatively coupled to the hot side (PV) across a vacuum gap. The coefficient of performance is maximized by using a highly luminescent material, such as GaAs, together with device structures that optimize extraction of the luminescence. We consider both a macroscopic vacuum gap and a sub-wavelength gap; the latter allows for evanescent coupling of photons between the devices, potentially providing a further enhancement to the efficiency of light extraction. Using device assumptions based on the current record-efficiency solar cells, we show that electroluminescent cooling can, in certain regimes of cooling power, achieve a higher coefficient of performance than thermoelectric cooling.