Bifacial near-field thermophotovoltaic converter with transparent intermediate substrate

Abstract

Thermophotovoltaic (TPV) converters generate electricity from thermal radiation by hot emitters powered by various heat sources. Near-field TPV converters achieve a significant increase in power output density through a sub-micron vacuum gap between the emitter and the photovoltaic (PV) cell, exploiting near-field thermal radiation. Recently, bifacial TPV converters, operating in the far-field regime, have been demonstrated to enhance efficiency by effectively recycling the sub-bandgap energy radiation. However, it brings a cooling challenge for the PV cell, necessitating lateral heat transfer to side edge cooling channels and demanding meticulous thermal engineering, especially at high power outputs. In this research, a bifacial near-field TPV converter with transparent intermediate substrates is introduced to boost both the power output density and efficiency. Intrinsic Si intermediate substrates envelop the PV cell, providing lateral cooling and mitigating surface mode photonic losses. Through a detailed analysis of design parameters, the efficacy of the design is demonstrated utilizing InAs cell to harvest 4.38 W/cm2 of electricity at 26.8% efficiency from 1000 K graphite emitters separated by 100 nm vacuum gaps. Despite the cooling challenge, the bifacial NF-TPV converter shows 2.4 times larger power output with a 2.7% point greater efficiency compared to conventional near-field TPV converter.