Visible-to-Near-IR Wide-Range Light Harvesting by Interfacial Charge-Transfer Transitions between TiO2 and p-Aminophenol and Evidence of Direct Electron Injection to the Conduction Band of TiO2
Visible-to-Near-IR Wide-Range Light Harvesting by Interfacial Charge-Transfer Transitions between TiO2 and p-Aminophenol and Evidence of Direct Electron Injection to the Conduction Band of TiO2
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DOI：
10.1021/acs.jpcc.7b06012
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发表时间：
2017-08-31
影响因子：
3.7
通讯作者：
Hanayat, Minoru
中科院分区：
文献类型：
--
作者：
Fujisawa, Jun-ichi;Eda, Takumi;Hanayat, Minoru
二氧化钛等宽禁带无机半导体与有机化合物之间的界面电荷转移(ICT)跃迁是一种特有的电子跃迁，即使使用无色的低分子有机化合物也能吸收可见光，也能直接将电子注入到二氧化钛中。由于这些特点，ICT转变有望成为光伏等太阳能转换中光吸收和光诱导电荷分离的一种新机制。然而，事实上，到目前为止报告的几乎所有信通技术过渡都局限在可见区域。通过ICT转换的可见光到近红外大范围光收集太阳能是这类应用的一个重要课题。此外，通常使用的ICT跃迁直接电子注入二氧化钛导带的图像仍有待于清楚地演示。为了解决这两个问题，本文研究了化学吸附了邻氨基苯酚、间氨基苯酚和对氨基苯酚的锐钛矿型纳米二氧化钛的ICT跃迁，这些纳米颗粒在不同的位置都含有一个给电子基。我们证明了由ICT跃迁产生的可见光到近红外光的大范围吸收是由对氨基苯酚产生的，最高可达1.1微米。此外，对ICT谱带的分析表明，ICT跃迁是从吸附的对氨基苯酚的最高占据分子轨道(HOMO)到二氧化钛的连续导带，而不是到离散的表面局域能级。这一结果为通过ICT跃迁直接将电子注入到二氧化钛的导带中提供了直接证据。我们的研究为ICT跃迁的光吸收和电子转移特性在太阳能转换中的应用提供了新的知识。
Interfacial charge-transfer (ICT) transitions between wide band gap inorganic semiconductors such as titanium dioxide (TiO2) and organic compounds are characteristic electronic transitions which enable the absorption of visible light even using colorless low-molecular-weight organic compounds and also direct electron injection into TiO2. Because of these features, ICT transitions are expected to be a new mechanism of light absorption and photoinduced charge separation for solar energy conversions such as photovoltaics. However, in fact, almost all ICT transitions reported so far are limited in the visible region. Visible-to-near-IR wide-range light harvesting of solar energy by ICT transitions is an important subject for such applications. In addition, the conventionally used picture of the direct electron injection into the conduction band of TiO2 by ICT transitions still remains to be demonstrated clearly. In order to solve the two issues, in this paper we study ICT transitions in anatase TiO2 nanoparticles chemically adsorbed with o-, m-, and p-aminophenol, which possess an electron-donating amino group at different positions. We demonstrate that visible-to-near-IR wide-range light absorption due to ICT transitions up to ca. 1.1 mu m is generated by using p-aminophenol. In addition, we reveal from the spectral analysis of the ICT band that the ICT transitions take place from the highest occupied molecular orbital (HOMO) of p-aminophenol adsorbates to the continuous conduction band of TiO2, not to discrete surface localized levels. This result offers a direct evidence of the direct electron injection into the conduction band of TiO2 by the ICT transitions. Our research provides novel, knowledge on the light absorption and electron transfer properties of ICT transitions for their applications to solar energy conversions.