Revealing the Origin of Fast Electron Transfer in TiO2-Based Dye-Sensitized Solar Cells

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• 作者：Hai Wei ; Jun-Wei Luo ; Shu-Shen Li ; Lin-Wang Wang
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：July 6, 2016
• 年：2016
• 卷：138
• 期：26
• 页码：8165-8174
• 全文大小：527K
• 年卷期：0
• ISSN：1520-5126

文摘

In dye-sensitized solar cells (DSCs), the electron transfer from photoexcited dye molecules to semiconductor substrates remains a major bottleneck. Replacing TiO₂ with ZnO is expected to enhance the efficiency of DSCs, owing to the latter possesses a much larger electron mobility, but similar bandgap and band positions as TiO₂ remain. However, the record efficiency of ZnO-based DSCs is only 7% compared with 13% of TiO₂-based DSCs due to the even slower electron-transfer rate in ZnO-based DSCs, which becomes a long-standing puzzle. Here, we computationally investigate the electron transfer from the dye molecule into ZnO and TiO₂, respectively, by performing the first-principles calculations within the frame of the Marcus theory. The predicted electron-transfer rate in the TiO₂-based DSC is about 1.15 × 10⁹ s^–1, a factor of 15 faster than that of the ZnO-based DSC, which is in good agreement with experimental data. We find that the much larger density of states of the TiO₂ compared with ZnO near the conduction band edge is the dominant factor, which is responsible for the faster electron-transfer rate in TiO₂-based DSCs. These denser states provide additional efficient channels for the electron transfer. We also provide design principles to boost the efficiency of DSCs through surface engineering of high mobility photoanode semiconductors.