Thermophotovoltaic cells are similar to solar cells, but instead of converting solar radiation to electricity, they are designed to utilize locally radiated heat. Development of high-efficiency thermophotovoltaic cells has the potential to enable widespread applications in grid-scale thermal energy storage 1 , 2 , direct solar energy conversion 3 – 8 , distributed co-generation 9 – 11 and waste heat scavenging 12 . To reach high efficiencies, thermophotovoltaic cells must utilize the broad spectrum of a radiative thermal source. However, most thermal radiation is in a low-energy wavelength range that cannot be used to excite electronic transitions and generate electricity. One promising way to overcome this challenge is to have low-energy photons reflected and re-absorbed by the thermal emitter, where their energy can have another chance at contributing towards photogeneration in the cell. However, current methods for photon recuperation are limited by insufficient bandwidth or parasitic absorption, resulting in large efficiency losses relative to theoretical limits. Here we demonstrate near-perfect reflection of low-energy photons by embedding a layer of air (an air bridge) within a thin-film In 0.53 Ga 0.47 As cell. This result represents a fourfold reduction in parasitic absorption relative to existing thermophotovoltaic cells. The resulting gain in absolute efficiency exceeds 6 per cent, leading to a very high power conversion efficiency of more than 30 per cent, as measured with an approximately 1,455-kelvin silicon carbide emitter. As the out-of-band reflectance approaches unity, the thermophotovoltaic efficiency becomes nearly insensitive to increasing cell bandgap or decreasing emitter temperature. Accessing this regime may unlock a range of possible materials and heat sources that were previously inaccessible to thermophotovoltaic energy conversion. An air gap embedded within the structure of a thermophotovoltaic device acts as a near-perfect reflector of low-energy photons, resulting in their recovery and recycling by the thermal source, enabling excellent power-conversion efficiency.

中文翻译：

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气桥热光伏电池中近乎完美的光子利用

热光伏电池类似于太阳能电池，但它们不是将太阳辐射转换为电能，而是设计为利用局部辐射热。高效热光伏电池的开发有可能在电网规模的热能储存 1 、 2 、直接太阳能转换 3 – 8 、分布式热电联产 9 – 11 和废热回收 12 中得到广泛应用。为了达到高效率，热光伏电池必须利用辐射热源的广谱。然而，大多数热辐射处于低能量波长范围内，不能用于激发电子跃迁和发电。克服这一挑战的一个有希望的方法是让低能光子被热发射器反射和重新吸收，他们的能量可以有另一个机会为细胞中的光生成做出贡献。然而，目前用于光子回收的方法受到带宽不足或寄生吸收的限制，导致相对于理论极限的较大效率损失。在这里，我们通过在薄膜 In 0.53 Ga 0.47 As 电池中嵌入一层空气（空气桥）来展示低能光子的近乎完美的反射。这一结果表明，相对于现有的热光伏电池，寄生吸收减少了四倍。由此产生的绝对效率增益超过 6%，从而产生超过 30% 的非常高的功率转换效率，用大约 1,455 开尔文的碳化硅发射极测量。随着带外反射率接近统一，热光伏效率对增加电池带隙或降低发射器温度几乎不敏感。访问该机制可能会解锁一系列可能的材料和热源，而这些材料和热源以前无法用于热光伏能量转换。嵌入在热光伏器件结构中的气隙充当低能光子的近乎完美的反射器，导致它们被热源回收和再循环，从而实现出色的功率转换效率。