Miriyala Kumaraswamy, Shor Peled Sa'ar, Klotz Dino, Grave Daniel A
Department of Materials Engineering, Ben-Gurion University of the Negev Beer Sheva 8410500 Israel
Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev Beer Sheva 8410500 Israel.
J Mater Chem A Mater. 2024 Dec 18;13(4):2965-2973. doi: 10.1039/d4ta05448b. eCollection 2025 Jan 21.
Zinc ferrite (ZnFeO, ZFO) has gained attention as a candidate material for photoelectrochemical water oxidation. However, champion devices have achieved photocurrents far below that predicted by its bandgap energy. Herein, strong optical interference is employed in compact ultrathin film (8-14 nm) Ti-doped ZFO films deposited on specular back reflectors to boost photoanode performance through enhanced light trapping, resulting in a roughly fourfold improvement in absorption as compared to films deposited on transparent substrates. The spatial charge carrier collection profile and wavelength-dependent photogeneration yield of mobile charge carriers was then extracted spatial collection efficiency analysis based on optical and external quantum efficiency measurements. We demonstrate that despite the enhanced performance enabled by the light trapping structure, substantial recombination occurs for thin film ZFO photoanodes even within the space charge region of an ultrathin film photoanode. Furthermore, the excitation-wavelength-dependent yield of mobile charge carriers in ZFO is shown to be less than unity across the visible spectrum, ultimately limiting the attainable photocurrent density. These results explain the underperformance of ZFO as a photoanode material and suggest that reduction of the mobile charge carrier yield due to the existence of ligand field states is a dominant loss mechanism for metal-oxides containing Fe metal centers with open d-shell configuration.
铁酸锌（ZnFeO，ZFO）作为一种用于光电化学水氧化的候选材料受到了关注。然而，目前的最佳器件所实现的光电流远低于其带隙能量所预测的值。在此，在沉积于镜面背反射器上的致密超薄膜（8 - 14纳米）掺钛ZFO薄膜中利用强光学干涉，通过增强光捕获来提高光阳极性能，与沉积在透明基板上的薄膜相比，吸收提高了约四倍。然后基于光学和外量子效率测量，通过空间收集效率分析提取了空间电荷载流子收集分布以及移动电荷载流子的波长相关光生率。我们证明，尽管光捕获结构提高了性能，但即使在超薄膜光阳极的空间电荷区域内，薄膜ZFO光阳极仍会发生大量复合。此外，ZFO中移动电荷载流子的激发波长相关产率在整个可见光谱范围内都小于1，最终限制了可达到的光电流密度。这些结果解释了ZFO作为光阳极材料性能不佳的原因，并表明由于配体场态的存在导致移动电荷载流子产率降低是具有开放d壳层构型的含Fe金属中心的金属氧化物的主要损耗机制。
