Improved Electron Transfer between TiO₂ and FTO Interface by N‑Doped Anatase TiO₂ Nanowires and Its Applications in Quantum Dot-Sensitized Solar Cells

The growth of anatase TiO₂ nanowires (NWs) on fluorine doped tin oxide (FTO) substrates through hydrothermal reaction has attracted wide attention and research, especially in the case of the solar cells. Actually, the built-in electric field at the anatase TiO₂ NWs/FTO interface leads to the photoexcited holes transfer to FTO conductive substrates because the Fermi energy of anatase TiO₂ NWs film is higher than that of FTO substrates. Yet efficient transport of photoexcited electron to the FTO conductive substrates is desirable. Hence, the built-in electric field at the pure TiO₂ NWs/FTO interface has prevented anatase TiO₂ NWs-based solar cells from achieving a higher photoelectric performance. In this work, we elaborately design and construct the N-doped anatase TiO₂ NWs/FTO interface with the desirable orientations from FTO toward N-doped anatase TiO₂ NWs, which favors the photoexcited electron transfer to the FTO conductive substrates. The surface photovoltage (SPV) and Kelvin probe measurements demostrate that the N-doped anatase TiO₂ NWs/FTO interface favors the photoexcited electron transfer to the FTO conductive substrates due to the fact that the orientation of the built-in electric field at the N-doped TiO₂ NWs/FTO interface is from FTO toward TiO₂. The photoexcited charge transfer dynamics of CdS QD-sensitized TiO₂ NWs and N-doped TiO₂ NWs electrodes was investigated using the transient photovoltage (TPV) and transient photocurrent (TPC) technique. Benefiting from the desirable interface electric field, CdS-based quantum dot-sensitized solar cells (QDSCs) with the optimal N doping amount exhibit a remarkable solar energy conversion efficiency of 2.75% under 1 sun illumination, which is 1.46 times enhancement as compared to the undoped reference solar cells. The results reveal that the N-doped anatase TiO₂ NWs electrodes have promising applications in solar cells