A hot-electron thermophotonic solar cell demonstrated by thermal up-conversion of sub-bandgap photons.

Daniel J Farrell,Masakazu Sugiyama,Yunpeng Wang,Hassanet Sodabanlu,Yoshitaka Okada

doi:10.1038/ncomms9685

Daniel J Farrell, Masakazu Sugiyama + Show 3 more

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https://doi.org/10.1038/ncomms9685

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Abstract

The direct conversion of solar energy to electricity can be broadly separated into two main categories: photovoltaics and thermal photovoltaics, where the former utilizes gradients in electrical potential and the latter thermal gradients. Conventional thermal photovoltaics has a high theoretical efficiency limit (84%) but in practice cannot be easily miniaturized and is limited by the engineering challenges of sustaining large (>1,000 K) temperature gradients. Here we show a hot-carrier-based thermophotonic solar cell, which combines the compact nature of photovoltaic devices with the potential to reach the high-efficiency regime of thermal photovoltaics. In the device, a thermal gradient of 500 K is established by hot electrons, under Stokes illumination, rather than by raising the temperature of the material itself. Under anti-Stokes (sub-bandgap) illumination we observe a thermal gradient of ∼20 K, which is maintained by steady-state Auger heating of carriers and corresponds to a internal thermal up-conversion efficiency of 30% between the collector and solar cell.

Highlights

The direct conversion of solar energy to electricity can be broadly separated into two main categories: photovoltaics and thermal photovoltaics, where the former utilizes gradients in electrical potential and the latter thermal gradients
Single junction solar cells are limited to efficiencies of o31% by the inability to absorb below-bandgap photons and the thermalization of photogenerated carriers to the band edges[1]
We demonstrate a thermophotonic device in which the thermal gradient is maintained by hot electrons in a quantum-well-based solar collector that is directly integrated into the device structure

Summary

Introduction

The direct conversion of solar energy to electricity can be broadly separated into two main categories: photovoltaics and thermal photovoltaics, where the former utilizes gradients in electrical potential and the latter thermal gradients. Photon energy light is transmitted and raises the temperature of the thermal collector located at the rear This configuration relies on thermal up-conversion in the solar collector to increase carrier energy such that some radiative recombination will occur with energy above the bandgap of the solar cell (the blue region in Fig. 1a) and contribute to additional photocurrent generation. In this way the solar collector becomes the second source of photons and the device concept can achieve an efficiency above that of the Shockley–Queisser limit[5]

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