We demonstrate an inverted metamorphic multijunction (IMM) photovoltaic cell comprising lattice-mismatched 1.2 eV AlGaInAs and 1.0 eV GaInAs junctions optimized for high-temperature thermophotovoltaic (TPV) applications. This device differs from traditional IMM solar cells because the mismatched junctions are grown at a single lattice constant. This architecture enables removal of the compositionally graded buffer that otherwise filters light from the junctions below and absorbs sub-bandgap light via free-carrier absorption. Sub-bandgap absorption dramatically reduces the efficiency of TPV systems using high reflectivity cells to enable band edge spectrum filtering. Three components required development to enable this device: (1) a lattice-mismatched 1.2 eV AlGaInAs junction, (2) a metamorphic contact layer grown after the graded buffer, and (3) a transparent tunnel junction that sits in front of the 1.0 eV GaInAs junction. Growth conditions that minimize oxygen defect incorporation maximize AlGaInAs cell quality, enabling a 0.41 V bandgap open circuit voltage offset at 22 mA/cm2 under AM1.5D. A mismatched GaInAs:Se layer is developed as a low resistance contact. Lastly, we develop a GaAsSb:C/GaInP:Se tunnel junction suitable for high-power densities with more transparency than the GaAsSb:C/GaInAs:Se structure used in past IMM cells. We characterize the tandem device under a high-intensity spectrum that approximates the emission from a 2150 °C blackbody radiator and deduce a projected ideal TPV efficiency of 39.9% at ∼30% of the blackbody irradiance and 36% ideal TPV efficiency under the full 118 W/cm2 irradiance. Improvements to the back-surface reflectivity and series resistance are expected to increase the ideal TPV efficiency well above 40%.

中文翻译：

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设计用于热能电网存储应用的倒变质 AlGaInAs/GaInAs 串联热光伏电池

我们展示了一种包含晶格失配的 1.2 eV AlGaInAs 和 1.0 eV GaInAs 结的倒变质多结 (IMM) 光伏电池，这些结针对高温热光伏 (TPV) 应用进行了优化。该器件不同于传统的 IMM 太阳能电池，因为失配结以单一晶格常数生长。这种架构能够去除成分渐变的缓冲液，否则该缓冲液会过滤来自下方结的光并通过自由载流子吸收吸收子带隙光。子带隙吸收显着降低了 TPV 系统的效率，该系统使用高反射率电池来实现带边缘频谱过滤。需要开发三个组件才能启用该器件：(1) 晶格失配的 1.2 eV AlGaInAs 结，(2) 在渐变缓冲之后生长的变质接触层，(3) 位于 1.0 eV GaInAs 结前面的透明隧道结。最大限度地减少氧缺陷掺入的生长条件可最大限度地提高 AlGaInAs 电池质量，从而在 AM1.5D 下以 22 mA/cm2 实现 0.41 V 带隙开路电压偏移。失配的 GaInAs:Se 层被开发为低电阻接触。最后，我们开发了适用于高功率密度的 GaAsSb:C/GaInP:Se 隧道结，其透明度比过去 IMM 电池中使用的 GaAsSb:C/GaInAs:Se 结构更高。我们在接近 2150 °C 黑体辐射器发射的高强度光谱下表征串联器件，并推导出在约 30% 的黑体辐照度下预计的理想 TPV 效率为 39.9%，在全 118°C 下的理想 TPV 效率为 36%。 W/cm2 辐照度。