Germanium solar cells are used as bottom subcells in many multijunction solar cell designs. The question remains whether the thermal load originated by the growth of the upper layers of the multijunction solar cell structure affects the Ge subcell performance. Here, we report and analyze the performance degradation of the Ge subcell due to such thermal load in lattice‐matched GaInP/Ga(In)As/Ge triple‐junction solar cells. Specifically, we have detected a quantum efficiency loss in the wavelength region corresponding to the emitter layer (which accounts for up to 20% loss in equivalent J_SC) and up to 55 mV loss in V_OC of the Ge subcell as compared with analogous devices grown as single‐junction Ge solar cells on the same type of substrates. We prove experimentally that there is no direct correlation between the loss in V_OC and the doping level of the base. Our simulations show that both the J_SC and V_OC losses are consistent with a degradation of the minority carrier properties at the emitter, in particular at the initial nanometers of the emitter next to the emitter/window heterointerface. In addition, we also rule out the gradual emitter profile shape as the origin of the degradation observed. Our findings underscore the potential to obtain higher efficiencies in Ge‐based multijunction solar cells if strategies to mitigate the impact of the thermal load are taken into consideration.

中文翻译：

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多结太阳能电池生长过程中热负荷对Ge子电池的降解

在许多多结太阳能电池设计中，锗太阳能电池都用作底部子电池。问题仍然在于，由多结太阳能电池结构上层的增长引起的热负荷是否会影响Ge子电池的性能。在这里，我们报告并分析了由于晶格匹配的GaInP / Ga（In）As / Ge三结太阳能电池中的此类热负荷而导致的Ge子电池的性能下降。具体而言，我们已经在与发射极层相对应的波长区域中检测到了量子效率损失（这相当于等效J _SC的损失高达20％）和V _OC的损失高达55 mV。与在相同类型的基板上生长为单结Ge太阳能电池的类似设备相比，Ge子电池的性能降低了。我们通过实验证明，存在的损失之间没有直接的关联V _OC和底座的掺杂水平。我们的仿真表明，J _SC和V _OC损耗与发射极处少数载流子特性的下降相一致，特别是在发射极/窗口异质界面旁边的发射极的初始纳米处。此外，我们还排除了逐渐变的发射器轮廓形状是观察到的退化的根源。我们的发现强调了如果考虑缓解热负荷影响的策略，Ge基多结太阳能电池有可能获得更高的效率。