Karalis Aristeidis, Joannopoulos J D
Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
Sci Rep. 2017 Oct 25;7(1):14046. doi: 10.1038/s41598-017-13540-8.
Transparent conducting electrodes play a fundamental role in far-field PhotoVoltaic systems, but have never been thoroughly investigated for near-field applications. Here we show, in the context of near-field planar ultra-thin ThermoPhotoVoltaic cells using surface-plasmon-polariton thermal emitters, that the resonant nature of the nanophotonic system significantly alters the design criteria for the necessary conducting front electrode. The traditional ratio of optical-to-DC conductivities is alone not an adequate figure of merit, instead the desired impedance matching between the emitter and absorber modes along with their coupling to the free-carrier resonance of the front electrode are key for optimal device design and performance. Moreover, we demonstrate that conducting electrodes 'opaque' to incoming far-field radiation can, in fact, be used in the near field with decent performance by taking advantage of evanescent photon tunneling from the emitter to the absorber. Finally, we identify and compare appropriate tunable-by-doping materials for front electrodes in near-field ThermoPhotoVoltaics, specifically molybdenum-doped indium oxide, dysprosium-doped cadmium oxide, graphene and diffused semiconductors, but also for 'opaque' electrodes, tin-doped indium oxide and silver nano-films. Predicted estimated performances include output power density ~10 W/cm with >45% efficiency at 2100 °K emitter temperature and 60 Ω electrode square resistance, thus increasing the promise for high-performance practical devices.
透明导电电极在远场光伏系统中起着基础性作用，但从未针对近场应用进行过深入研究。在此，我们表明，在使用表面等离激元极化子热发射器的近场平面超薄热光伏电池的背景下，纳米光子系统的共振特性显著改变了对必要导电前电极的设计标准。传统的光导率与直流电导率之比本身并不是一个足够的品质因数，相反，发射器和吸收器模式之间所需的阻抗匹配以及它们与前电极自由载流子共振的耦合对于优化器件设计和性能至关重要。此外，我们证明，对入射远场辐射“不透明”的导电电极，实际上可以通过利用从发射器到吸收器的倏逝光子隧穿，在近场中以良好的性能使用。最后，我们识别并比较了近场热光伏中前电极适用的可通过掺杂调节的材料，特别是掺钼氧化铟、掺镝氧化镉、石墨烯和扩散半导体，同时也适用于“不透明”电极的掺锡氧化铟和银纳米膜。预测的估计性能包括在2100°K发射器温度和60Ω电极方电阻下，输出功率密度约为10W/cm²，效率大于45%，从而增加了高性能实用器件的前景。
