Extraction of mobile charge carrier photogeneration yield spectrum of ultrathin-film metal oxide photoanodes for solar water splitting
Extraction of mobile charge carrier photogeneration yield spectrum of ultrathin-film metal oxide photoanodes for solar water splitting
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DOI：
10.1038/s41563-021-00955-y
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发表时间：
2021-04-19
期刊：
影响因子：
41.2
通讯作者：
Rothschild, Avner
中科院分区：
文献类型：
--
作者：
Grave, Daniel A.;Ellis, David S.;Rothschild, Avner
强关联电子材料中的光吸收可以激发电子和空穴进入各种不同的状态。这些激发中的一些产生移动的电荷载流子，而另一些导致不能对光电流有贡献的局域态。光生产率光谱xi（lambda）表示最终产生移动的电荷载流子的贡献吸收与总吸收之间的波长依赖性比率。尽管它是一种重要的物质属性，但它的特征并不简单。在这里，我们提出了一个经验的方法来提取xi（λ）通过光学和外部量子效率测量的薄膜。我们将此方法应用于赤铁矿光阳极的水的光氧化，并观察到它是自洽的不同的光照条件和施加的电位。我们发现提取的XI（λ）光谱和时间分辨微波电导率测量的光电导谱之间的协议。这些测量结果表明，移动的电荷载流子的产生随着整个赤铁矿的吸收光谱的能量的增加而增加。低能量非贡献吸收从根本上限制了赤铁矿光阳极的光转换效率，并提供了可实现的光电流的上限，该上限基本上低于仅基于带隙以上的吸收所预测的上限。我们将我们的分析扩展到TiO2和BiVO4光阳极，证明了确定xi（lambda）的方法的更广泛的实用性。虽然光生产额光谱是光伏和光电化学电池中光吸收剂的关键特性，但其表征仍然具有挑战性。提出了一种经验方法来提取这个参数，通过量子效率测量的薄膜。
Light absorption in strongly correlated electron materials can excite electrons and holes into a variety of different states. Some of these excitations yield mobile charge carriers, whereas others result in localized states that cannot contribute to photocurrent. The photogeneration yield spectrum, xi(lambda), represents the wavelength-dependent ratio between the contributing absorption that ultimately generates mobile charge carriers and the overall absorption. Despite being a vital material property, it is not trivial to characterize. Here, we present an empirical method to extract xi(lambda) through optical and external quantum efficiency measurements of ultrathin films. We applied this method to haematite photoanodes for water photo-oxidation, and observed that it is self-consistent for different illumination conditions and applied potentials. We found agreement between the extracted xi(lambda) spectrum and the photoconductivity spectrum measured by time-resolved microwave conductivity. These measurements revealed that mobile charge carrier generation increases with increasing energy across haematite's absorption spectrum. Low-energy non-contributing absorption fundamentally limits the photoconversion efficiency of haematite photoanodes and provides an upper limit to the achievable photocurrent that is substantially lower than that predicted based solely on absorption above the bandgap. We extended our analysis to TiO2 and BiVO4 photoanodes, demonstrating the broader utility of the method for determining xi(lambda).Although the photogeneration yield spectrum is a key property for photoabsorbers in photovoltaic and photoelectrochemical cells, its characterization remains challenging. An empirical method to extract this parameter through quantum efficiency measurements of ultrathin films is proposed.