Solar cells containing a polycrystalline Cu(In,Ga)Se₂ absorber outperform the ones containing a monocrystalline absorber, showing a record efficiency of 22.9%. However, the grain boundaries (GBs) are very often considered to be partly responsible for the enhanced recombination activity in the cell and thus cannot explain the registered record efficiency. Therefore, in the present work, we resolve this conundrum by performing correlative electron beam-induced current–electron backscatter diffraction investigations on more than 700 grain boundaries and demonstrating that 58% of the grain boundaries exhibit an enhanced carrier collection compared to the grain interior. Enhanced carrier collection thus indicates that GBs are beneficial for the device performance. Moreover, 27% of the grain boundaries are neutral and 15% are recombination-active. Correlation with microstructure shows that most of the ∑3 GBs are neutral, whereas the random high-angle grain boundaries are either beneficial or detrimental. Enhanced carrier collection observed for a big fraction of high-angle grain boundaries supports the “type-inversion” model and hence the downward band bending at GBs. The decrease in current collection observed at one of the high-angle grain boundaries is explained by Cu being enriched at this GB and hence by the upward shift of the valence band maximum.

中文翻译：

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Cu（In，Ga）Se ₂晶界中增强的载流子收集的证据：与微观结构的关系。

包含多晶Cu（In，Ga）Se _2的太阳能电池吸收剂的性能优于包含单晶吸收剂的吸收剂，显示出创纪录的22.9％的效率。但是，晶界（GBs）通常被认为是造成细胞中重组活性增强的部分原因，因此不能解释记录的效率。因此，在目前的工作中，我们通过对700多个晶界进行相关的电子束感应电流-电子反向散射衍射研究，并证明与晶粒内部相比，58％的晶界表现出了增强的载流子收集，从而解决了这个难题。因此，增强的载波收集功能表明GB有益于设备性能。此外，27％的晶界是中性的，而15％的是具有重组活性的。与微观结构的关系表明，大多数∑3 GB是中性的，而随机的高角度晶界则是有益的或有害的。对于大部分高角度晶界观察到的增强的载流子收集支持“类型反转”模型，因此支持了GBs处的向下带弯曲。在高角度晶界之一处观察到的电流收集的减少是由于铜在该GB处富集，并因此由价带最大值的向上移动所解释。