Solid solutions between ZnSe and Cu(In, Ga)Se₂ (ZnSe:CIGS) have promising properties as photocathodes for solar hydrogen production from water, such as a long absorption edge of about 900 nm and a large driving force for reaction, >0.9 V, originated by a deep valence band maximum of 1.0–1.1 V vs normal hydrogen electrode (NHE). However, their performance is limited with an incident photon-to-current conversion efficiency (IPCE) of 65% at 400 nm and a half-cell solar-to-hydrogen energy conversion efficiency (HC-STH) of 3.6% so far. Te addition during ZnSe:CIGS thin film deposition by vacuum co-evaporation clearly decreased the optimal deposition temperature from 450 to 380 °C and resulted in columnar shaped grains of submicrometer size in diameter and with almost no grain boundary between the film surface and the backside electrode of Mo, which is significantly larger than the case of without Te addition. Interestingly, a Ga/In compositional ratio gradient was further introduced to the depth profile, which can facilitate charge separation. Structural characterizations using XRD and cross-sectional transmission electron microscopy revealed that the composition gradient was mainly formed by the diffusion of In through grain boundaries in the Ga-rich layer, and thus, the mixing between the Ga-rich and In-rich layers was more significant at a lower deposition temperature owing to the smaller grain size. The photocathode fabricated from the ZnSe:CIGS thin film with the composition gradient showed a very high IPCE of 89% at 540 nm and 0 V vs the reversible hydrogen electrode, and HC-STH of 3.7%, which is higher than values reported thus far. In conclusion, it is clarified that the potential gradient, which can be introduced by composition gradient, is beneficial for photoelectrodes and photocatalysts to achieve higher performance.

中文翻译：

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ZnSe 和 Cu(In, Ga)Se2 之间具有成分梯度的固溶体组成的薄膜光电阴极上从水有效析氢

ZnSe 和 Cu(In, Ga)Se ₂之间的固溶体(ZnSe:CIGS) 作为太阳能从水中制氢的光电阴极具有有前途的特性，例如约 900 nm 的长吸收边和大的反应驱动力，> 0.9 V，源于 1.0-1.1 的深价带最大值V vs 普通氢电极 (NHE)。然而，到目前为止，它们的性能受到 400 nm 处 65% 的入射光子到电流转换效率 (IPCE) 和 3.6% 的半电池太阳能到氢能转换效率 (HC-STH) 的限制。通过真空共蒸发在 ZnSe:CIGS 薄膜沉积过程中添加 Te 明显将最佳沉积温度从 450°C 降低到 380°C，并导致直径亚微米级的柱状晶粒，并且薄膜表面和背面之间几乎没有晶界钼电极，这明显大于不添加 Te 的情况。有趣的是，在深度剖面中进一步引入了 Ga/In 组成比梯度，这可以促进电荷分离。使用XRD和横截面透射电子显微镜的结构表征表明，成分梯度主要由In通过富Ga层中的晶界扩散形成，因此，富Ga层和富In层之间的混合是由于较小的晶粒尺寸，在较低的沉积温度下更显着。由具有组成梯度的 ZnSe:CIGS 薄膜制成的光电阴极与可逆氢电极相比，在 540 nm 和 0 V 下显示出 89% 的非常高的 IPCE，以及​​ 3.7% 的 HC-STH，高于迄今为止报道的值. 综上所述，