Thermally enhanced photoluminescence for heat harvesting in photovoltaics

Abstract

The maximal Shockley–Queisser efficiency limit of 41% for single-junction photovoltaics is primarily caused by heat dissipation following energetic-photon absorption. Solar-thermophotovoltaics concepts attempt to harvest this heat loss, but the required high temperatures (T>2,000 K) hinder device realization. Conversely, we have recently demonstrated how thermally enhanced photoluminescence is an efficient optical heat-pump that operates in comparably low temperatures. Here we theoretically and experimentally demonstrate such a thermally enhanced photoluminescence based solar-energy converter. Here heat is harvested by a low bandgap photoluminescent absorber that emits thermally enhanced photoluminescence towards a higher bandgap photovoltaic cell, resulting in a maximum theoretical efficiency of 70% at a temperature of 1,140 K. We experimentally demonstrate the key feature of sub-bandgap photon thermal upconversion with an efficiency of 1.4% at only 600 K. Experiments on white light excitation of a tailored Cr:Nd:Yb glass absorber suggest that conversion efficiencies as high as 48% at 1,500 K are in reach.

Photoluminescence of Doped YAG Transparent Ceramics Fabricated by Spark Plasma Sintering

“…After optimization of the fabrication process for single‐doped YAG, SPS can now be applied to develop multi‐doped YAG for more advanced and innovative applications. As an example, it is demonstrated for such materials which could be used to tailor the sunlight spectrum for more efficient solar energy harvesting . Potentially, a photoluminescent absorber/emitter material (such as multi‐doped ceramics) would be set between the sun and the solar cell.…”

Thermally enhanced photoluminescence for ultra-high-efficiency photovoltaics

“…On the basis of our successful experiments, we have recently proposed a TEPL-based PV converter. 6 At the heart of this device-see Figure 3(a)-is a PL material that has an absorption cut-off energy (E Abs ). In the converter, the absorption of solar photons excites PL and raises the absorber's temperature (because of the electron thermalization that follows energetic photon absorption).…”

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

“…By coupling the blueshifted emission of a low bandgap PL absorber to a high bandgap PV cell, we benefit from a high current and high voltage, potentially surpassing the SQ limit. The theoretical maximal efficiency for such a concept is 70% and a practical device is expected to work at efficiencies as high as 45% [7], exceeding the SQ limit of 32% and 38% for single junction solar cells under 1 and 1000 suns, respectively. These high efficiencies also require efficient photonic management, where nonabsorbed photons are re-absorbed into the PL material.…”

“…Thus far, TEPL was demonstrated only as a proof of concept with up-conversion efficiency of 2.5% at narrow band excitation [7], as the materials used were not optimized for maximal solar absorption or for retaining the high emission external quantum efficiency (EQE) at high temperatures.…”

“…Here we study the performance of various absorber materials for TEPL under simulated solar excitation-specifically, Nd 3+ sensitized by Cr 3+ in YAG and GSGG crystal matrices. To better understand the criterion for a 'good' TEPL absorber, we examine its role as laid out in reference [7]. It must, as its name suggests, absorb the solar spectrum effectively, transforming this excitation into PL emission.…”