The remarkable morphology regulatory effect of NH4+ ions on TiO2 nanorod arrays and their application in dye-sensitized solar cells
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Nitrogen doping is often used to expand the response range of wide-bandgap semiconductors to improve their photoelectrical properties. Unique morphology regulatory effect of NH4+ ions on one-dimensional TiO2 nanorod arrays (TNAs) is proved in this research for the first time, but nitrogen-doping effect is hardly detected. Once NH4Cl is added, the growth of TNAs is greatly promoted especially in radial direction, but little amount of nitrogen from NH4+ ions can enter the modified TNAs (N-TNAs). Furthermore, the bandgap energy of N-TNAs is almost unchanged compared with TNAs, meaning that trace nitrogen doping does not affect response ability to irradiation. When fabricated into dye-sensitized solar cells (DSSCs) with N-TNAs, the optimal photoelectrical conversion efficiency (3.16%) is nearly twice that with TNAs (1.62%). It is worth noting that the increased efficiency mainly results from the photoinduced current but not voltage. Second, the change of conversion efficiency is related to nanorod length. In summary, the improvement of photoelectrical property is caused by the directional growth of nanorods, which results from the addition of NH4+ ions as an effective structure regulatory agent.
This work was partially supported by the National Natural Science Foundation of China (21776147, 21606140, and 61604086), the Open Project Program of the State Key Laboratory of Photocatalysis on Energy and Environment (SKLPEE-KF201707) at Fuzhou University, the Department of Science and Technology of Shandong Province (2016GGX104010 and ZR2018BB066), and the Department of Education of Shandong Province (J16LA14 and J17KA013). L. F. Dong also thanks financial support from the Malmstrom Endowment Fund of Hamline University.