物理学报2018，Vol.67Issue(2)：121-129,9.DOI:10.7498/aps.67.20171531
用于热光伏系统的近场辐射光谱控制表面结构
Surface structure for manipulating the near-field spectral radiative transfer of thermophotovoltaics
摘要
Abstract
To improve the efficiency and output power of the nano-gap thermophotovoltaic (TPV) power generation system, surface rectangular grating structures are added to the top surface of the group III-V semiconductor cell to control the spectrum of near-field radiative transfer. Doped zinc oxide that supports surface waves at near-infrared wavelengths is selected as the TPV emitter. When paired with GaSb grating structures, the surface plasmon polariton excited by the emitter and the light trapping effect by the grating tunnels will be coupled,which results in a significantly and selectively enhanced near-field radiative heat flux within a narrow spectral region above the cell bandgap,thereby fulfilling the design purpose. This physical mechanism is explained by a direct finite-difference time-domain(FDTD)simulation based on the Langevin approach. The material volume meshgrids filled with random dipole sources can act as the thermal emission source and the radiative heat flux is calculated by solving the Maxwell equations numerically. The spectral results show that adding rectangular grating structures to GaSb not only increases radiative transfer in the expected wavelength region over the unstructured case, resulting in a heat flux surpassing that of a far-field blackbody source at the same temperature, but also suppresses the unwanted long-wavelength heat flux that causes radiative loss and cell heating. With a vacuum gap of 200 nm between the emitter and the cell, using a bulk GaSb cell with rectangular gratings can double the spectral flux of the blackbody emitter case, and using an ultrathin GaSb cell with surface structures and back reflectors further increases this ratio to 2.84 due to the total internal reflection controlled by the cell thickness. The amplitude and wavelength of the spectral peak are controlled by the grating size parameters. Low filling ratio gratings with lower-aspect-ratio grating channels generally have sharper enhancement peaks but lower total radiative heat flux, while high filling ratio structures with higher-aspect-ratio channels have better heat flux improvement but might also result in lower conversion efficiency due to the broader spectrum. The rigorous approach reveals the detailed physical mechanism that is otherwise unseen with effective medium approaches for inhomogeneous structures or the Derjaguin proximity approximation. Overall the results of this study enable an enhancement of near-field radiative heat flux limited within a narrow wavelength range shorter than the cell bandgap, offering practical benefit to the application of TPV power generation with higher feasible power and conversion efficiency.关键词
近场辐射/光谱控制/热光伏系统/时域有限差分法Key words
near-field radiation/spectral control/thermophotovoltaic system/finite-difference time-domain method引用本文复制引用
于海童,刘东,杨震,段远源..用于热光伏系统的近场辐射光谱控制表面结构[J].物理学报,2018,67(2):121-129,9.基金项目
国家自然科学基金(批准号:51621062, 51606099)资助的课题. Project supported by the National Natural Science Foundation of China (Grant Nos. 51621062, 51606099). （批准号:51621062, 51606099）
