Thin-film 'Thermal Well' Emitters and Absorbers for High-Efficiency Thermophotovoltaics

TL;DR

This paper proposes a novel thin-film 'thermal well' design for thermophotovoltaics that significantly enhances efficiency by spectral control and reduced recombination, achieving near-field efficiencies up to 38.7%.

Contribution

It introduces a simple, low-cost thin-film approach to improve TPV efficiency without nanoscale patterning, utilizing photon confinement in waveguide modes.

Findings

Near-field TPV efficiency up to 38.7% with Ge emitter and GaSb cell.

Far-field efficiency predicted at 31.5%, surpassing Shockley Queisser limit.

Spectral selectivity achieved through photon confinement in thin films.

Abstract

A new approach is introduced to significantly improve the performance of thermophotovoltaic (TPV) systems by using low-dimensional thermal emitters and photovoltaic (PV) cells. By reducing the thickness of both the emitter and the PV cell, strong spectral selectivity in both thermal emission and absorption can be achieved by confining photons in trapped waveguide modes inside the thin-films that act as thermal analogs to quantum wells. Simultaneously, photo-excited carriers travel shorter distances across the thin-films reducing bulk recombination losses resulting in a lower saturation current in the PV cell. We predict a TPV efficiency enhancement with near-field coupling between the thermal emitter and the PV cell of up to 38.7% using a germanium (Ge) emitter at 1000 K and a gallium antimonide (GaSb) cell with optimized thicknesses separated by 100 nm. Even in the far-field limit, the efficiency is predicted to reach 31.5%, which is an order of magnitude higher than the Shockley Queisser limit of 1.6% for a bulk GaSb cell and a blackbody emitter at 1000 K. The proposed design approach does not require nanoscale patterning of the emitter and PV cell surfaces, but instead offers a simple low-cost solution to improve the performance of a thermophotovoltaic system.