Thermally enhanced photoluminescence for energy harvesting: from fundamentals to engineering optimization

TL;DR

This paper explores thermally enhanced photoluminescence (TEPL) as a novel method for energy harvesting, demonstrating its fundamental principles, experimental validation, and potential for high-efficiency photovoltaic applications.

Contribution

It advances TEPL from theoretical understanding to practical engineering, using Cr:Nd:YAG as a device material for solar energy conversion.

Findings

TEPL can generate more energetic photons than thermal emission at similar temperatures.

A device using Cr:Nd:YAG can achieve up to 34% power conversion efficiency.

TEPL has potential to reach 45-70% efficiency in photovoltaic energy harvesting.

Abstract

The radiance of thermal emission, as described by Planck law, depends only on the emissivity and temperature of a body, and increases monotonically with the temperature rise at any emitted wavelength. Nonthermal radiation, such as photoluminescence, is a fundamental light matter interaction that conventionally involves the absorption of an energetic photon, thermalization, and the emission of a redshifted photon. Such a quantum process is governed by rate conservation, which is contingent on the quantum efficiency. In the past, the role of rate conservation for significant thermal excitation had not been studied. Recently, we presented the theory and an experimental demonstration that showed, in contrast to thermal emission, that the PL rate is conserved when the temperature increases while each photon is blueshifted. A further rise in temperature leads to an abrupt transition to thermal emission where the photon rate increases sharply. We also demonstrated how such thermally enhanced PL, TEPL, generates orders of magnitude more energetic photons than thermal emission at similar temperatures. These findings show that TEPL is an ideal optical heat pump that can harvest thermal losses in photovoltaics with a maximal theoretical efficiency of 70%, and practical concepts potentially reaching 45% efficiency. Here we move the TEPL concept onto the engineering level and present Cr:Nd:YAG as device grade PL material, absorbing solar radiation up to 1 micrometer wavelength and heated by thermalization of energetic photons. Its blueshifted emission, which can match GaAs cells, is 20% of the absorbed power. Based on a detailed balance simulation, such a material coupled with proper photonic management can reach 34% power conversion efficiency. These results raise confidence in the potential of TEPL becoming a disruptive technology in photovoltaics.