The space charges and the radiation heat in the interelectrode space have been thought as the sources of the major irreversible losses of micro-scale vacuum gap thermionic emission devices. By focusing on the photo-enhanced thermionic emission (PETE) solar cell, the space-dependent expressions of the space charge effect and near field radiation loss are derived. The coupled balance equations of energy and carrier are considered to determine the carrier concentration and temperature of the cathode. The space charge limited regions and principal energy fluxes of the cathode are discussed at different interelectrode spaces and environmental changes. The maximum efficiency is calculated by optimizing the operating voltage and interelectrode space. The optimal gap ranges are also revealed, which is comparable to the characteristic wavelength of thermal radiation given by Wien’s displacement law. Our investigation will provide an effective way to optimally design the structure of the PETE device.

电极间空间中的空间电荷和辐射热被认为是微型真空间隙热电子发射装置的主要不可逆损耗的来源。通过关注光增强热电子发射（PETE）太阳能电池，推导了空间电荷效应和近场辐射损耗的空间依赖表达式。考虑能量和载流子的耦合平衡方程，以确定阴极的载流子浓度和温度。在不同的电极间空间和环境变化下讨论了阴极的空间电荷受限区域和主能通量。通过优化工作电压和电极间空间可以计算出最大效率。最佳间隙范围也被揭示出来，这可以与维恩位移定律给出的热辐射特征波长相媲美。我们的研究将为优化设计PETE装置的结构提供一种有效的方法。