Nano-Gap Thermophotovoltaic Generation of Electricity using Spectral Controlled Near-Field Radiation

研究了近场辐射（倏逝波）对热光伏发电的增强作用。在真空室中，将钨发射极和GaSb TPV电池面对面放置在一起。用CO_2激光器加热发射体，并保持在950 K。将TPV电池安装在水冷铜块上并保持在大气温度下。在差距小于50μm的条件下，由于传输辐射的视角因子几乎为1，输出功率基本不变。另一方面，在间隙进一步减小到小于1 μ m时，由于近场效应，开路电压和短路电流分别增加1.4倍和4倍。其结果是，在近场辐射的情况下的最大功率是5.6倍高于通常的传播辐射。在这种情况下，商业TPV电池在其表面上具有指状电极;使得其不适合于纳米间隙TPV能量转换系统。因此，利用分子束外延设备，我们尝试制作一个原始的电池，其中电极将浸没在p型半导体中以制作平坦的表面。在高真空室中，在n型GaSb衬底上生长了p型GaSb层。电池的载流子密度和迁移率分别为5.73 × 10^7cm ^2<-3>和1.35 × 10^2cm ^2/Vs。此外，GaSb TPV电池在0.8 - 1.8μm波长范围内是有效的。因此，来自发射器的辐射集中在这个波长范围内。具有微腔的表面可用于辐射发射的光谱控制。具有500 × 500 × 500nm^3微腔的表面在0.8μm至1.5μm波长范围内具有高发射率。因此，可以预期，只要将这些结合起来，通过近场效应从热能到电能的新的复杂的能量转换系统将在不久的将来被成功地开发。

Effect of near-field radiation (evanescent wave) to enhancement of thermophotovoltaic (TPV) generation of electricity has been investigated in the current study. A tungsten emitter and a GaSb TPV cell were put together in face to face in vacuum chamber. The emitter was heated by CO_2 laser and kept at 950K. The TPV cell was mounted on a water-cooled copper block and kept at atmospheric temperature. Under the condition of the gap less than 50μm, the output power does not change since the view factor is almost unity for the propagating radiation. On the other hand, on further decrease in gap to less 1 pm, the open circuit voltage and the short circuit current increase by a factor of 1.4 and 4, respectively due to the near-field effect. As a result, the maximum power in the case of near-field radiation is 5.6 times higher than that of usual propagating radiation. In this case, the commercial TPV cell has finger electrodes on its surface; so that it is not suitable for the nano-gap TPV energy-conversion system. Therefore, using the MBE equipment, we tried to fabricate an original cell, in which the electrode will be submerged in the p-type semiconductor to make a flat surface. In a high vacuum chamber, p-type GaSb layer was grown on the n-type GaSb substrate. The carrier density and the mobility of cell were 5.73x10^7cm^<-3> and 1.35x10^2cm^2/Vs, respectively. Furthermore, the GaSb TPV cell is active for the wavelength from 0.8 to 1.8μm. So, the radiation come from the emitter is concentrated in this wavelength range. A surface with micro-cavities is useful for the spectral control of emission of radiation. A surface with micro-cavities of 500x500x500nm^3 has a high emittance in the wavelength range from 0.8μm to 1.5μm. Consequently, it will be expected that, provided that those are combined, a new sophisticated energy conversion system from thermal energy to electricity through near-field effect will be developed successfully in near future.