The bandgap of CuIn1- x Gax Se2 (CIGS) chalcopyrite semiconductors can be tuned between ≈1.0 and ≈1.7 eV for Ga contents ranging between x = 0 and x = 1. While an optimum bandgap of 1.34 eV is desirable for achieving maximum solar energy conversion in solar cells, state-of-the-art CIGS-based devices experience a drop in efficiency for Ga contents x > 0.3 (i.e., for bandgaps >1.2 eV), an aspect that is limiting the full potential of these devices. The mechanism underlying the limited performance as a function of CIGS composition has remained elusive: both surface and bulk recombination effects are proposed. Here, the disentanglement between surface and bulk effects in CIGS absorbers as a function of Ga content is achieved by comparing photogenerated charge carrier dynamics in air/CIGS and surface-passivated ZnO/CdS/CIGS samples. While surface passivation prevents surface recombination of charge carriers for low Ga content (x < 0.3; up to 1.2 eV bandgap), surface recombination dominates for higher-bandgap materials. The results thus demonstrate that surface, rather than bulk effects, is responsible for the drop in efficiency for Ga contents larger than x ≈ 0.3.

中文翻译：

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CdS / CuIn1- x Gax Se2接口处的成分相关钝化效率。

对于Ga含量在x = 0和x = 1之间的CuIn1-x Gax Se2（CIGS）黄铜矿半导体，其带隙可以在≈1.0和≈1.7eV之间调整。在太阳能电池转换中，基于CIGS的最先进器件在Ga含量x> 0.3（即，带隙> 1.2 eV）时效率会下降，这是限制这些器件的全部潜力的一个方面。作为CIGS成分的函数，有限的性能所依据的机理仍然难以捉摸：提出了表面和本体复合效应。在这里，通过比较空气/ CIGS和表面钝化的ZnO / CdS / CIGS样品中的光生电荷载流子动力学，可以实现CIGS吸收剂中表面效应和体积效应之间的纠缠与Ga含量的关系。虽然表面钝化阻止了低Ga含量（x <0.3；高达1.2 eV带隙）的载流子的表面重组，但对于带隙较高的材料，表面复合起着主导作用。因此结果表明，Ga含量大于x≈0.3时，效率下降是由表面而不是体积效应引起的。