The power conversion efficiency of solar cells strongly depends on the open-circuit voltage which, in turn, depends on the recombination activity within the device. A possible source of detrimental charge carrier recombination is band tails. An empirical linear relationship between loss and the Urbach energy of the band tails has been shown in the past. Here we discuss how band tails influence the radiative recombination and the nonradiative recombination in the bulk of the absorber. First, we show through photoluminescence that the band tails can be willfully tuned in state-of-the-art thin-film Cu (In,Ga)Se₂ (CIGSe) absorbers and solar cells on a 20% efficiency level and beyond through the incorporation of alkali atoms. In the second part, we compare our CIGSe results to published results from other solar cell technologies. This comparison reveals that CIGS solar cells follow the previously described empirical trend: an increase in the open-circuit voltage with decreasing band tails. Finally, we model the influence of tail states on the radiative and nonradiative recombination losses: Radiative recombination is increased because carriers thermalize into the tail states and nonradiative recombination of free carriers in the bands is increased because of Shockley–Read–Hall recombination through the tail states. The comparison with experimental data shows that the influence of tail states is even worse than the increase in radiative and SRH recombination predicted by our model. Our results thus suggest that band tails act as one of the main remaining voltage limitations in the majority of state-of-the-art solar cells.

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带尾复合如何影响太阳能电池的开路电压

太阳能电池的功率转换效率很大程度上取决于开路电压，而开路电压又取决于器件内的复合活动。有害电荷载流子重组的一个可能来源是带尾。过去已经显示了损耗和带尾的 Urbach 能量之间的经验线性关系。在这里，我们讨论带尾如何影响吸收体中的辐射复合和非辐射复合。首先，我们通过光致发光表明带尾可以在最先进的薄膜 Cu (In,Ga)Se _{2中任意调节}(CIGSe) 吸收器和太阳能电池通过加入碱原子，效率达到 20% 甚至更高。在第二部分中，我们将我们的 CIGSe 结果与其他太阳能电池技术的已发表结果进行了比较。这种比较表明，CIGS 太阳能电池遵循先前描述的经验趋势：开路电压随着带尾减小而增加。最后，我们模拟了尾态对辐射和非辐射复合损失的影响：由于载流子热化为尾态，辐射复合增加，而带中自由载流子的非辐射复合增加，因为 Shockley-Read-Hall 复合通过尾部状态。与实验数据的比较表明，尾态的影响甚至比我们模型预测的辐射和 SRH 重组的增加还要糟糕。因此，我们的结果表明，带尾是大多数最先进的太阳能电池中主要的剩余电压限制之一。