Near-field thermophotonic system overcoming electrode losses

Current solid-state power generation technologies from mid-grade (∼600 K) heat sources face limitations in electrical power density and efficiency. Near-field thermophotonic systems show promise, leveraging amplified spontaneous emission from a hot LED and enhanced photon tunneling through a nanogap. However, high performance is only predicted when shading and series resistance losses from the front contact electrode (FCE) are not considered. Here, we present a system using indium tin oxide (ITO) FCE to mitigate these losses and achieve high performance. Unlike conventional Au grating FCE, ITO FCE remains transparent in the above-bandgap regime, significantly reducing loss by shading. As a transparent intermediate layer, ITO supports near-field radiative heat transfer at opposing ITO surfaces without significantly impeding photon transmission from LED to PV cell, even when it is relatively thick. This allows for increased thickness of ITO FCE and reduced series resistance. Additionally, mismatched plasma frequencies of the two ITO electrodes suppress low-energy photon transfer via surface modes, enhancing system efficiency. With a 600 K heat source and a 100 nm gap size, the system with ITO electrodes achieves a power density of 0.176 W/cm2 and an efficiency of 10.9 %. Compared to systems with Au grating electrodes, this represents a 3.75-fold increase in power density and a 2.98-fold improvement in efficiency. Wave interference in ITO FCE suggests optimal system parameters. Furthermore, incorporating a multi-junction PV cell provides an additional enhancement of 18.2 % in power density. This work paves the way for high-performance electricity generation from mid-grade heat sources.