Thermophotovoltaic energy conversion in far-to-near-field transition regime

TL;DR

This study experimentally demonstrates oscillatory near-field thermophotovoltaic energy conversion in the far-to-near-field transition regime, revealing phenomena caused by interference of propagating waves and suggesting alternative design strategies for improved TPV systems.

Contribution

It uncovers the oscillatory behavior of TPV energy conversion in the transition regime and shows that comparable photocurrents can be achieved at different gaps, offering new design insights.

Findings

Photocurrent oscillates with vacuum gap size.

Same photocurrent at 870 nm and 322 nm gaps, exceeding far-field performance.

Interference of propagating waves influences near-field TPV energy conversion.

Abstract

Recent experimental studies on near-field thermophotovoltaic (TPV) energy conversion have mainly focused on enhancing performance via photon tunneling of evanescent waves. In the sub-micron gap, however, there exist peculiar phenomena caused by the interference of propagating waves, which is seldom observed due to the dramatic increase of the radiation by evanescent waves in full spectrum range. Here, we experimentally demonstrate the oscillatory nature of near-field TPV energy conversion in the far-to-near-field transition regime (250-2600 nm), where evanescent and propagating modes are comparable due to the selective spectral response by the PV cell. Noticeably, it was possible to produce the same amount of photocurrent at different vacuum gaps of 870 and 322 nm, which is 10\% larger than the far-field value. Considering the great challenges in maintaining nanoscale vacuum gap in practical devices, this study suggests an alternative approach to the design of a TPV system that will outperform conventional far-field counterparts.