Enhanced open-circuit voltage of dye-sensitized solar cells using Bi-doped TiO2 nanofibers as working electrode and scattering layer

Doping metal-ion into TiO2 materials is an effective method for enhancing the performance of dye-sensitized solar cells (DSSCs). In order to develop materials that are easy to produce even in industrial quantities, we established a facile method by hydrothermal synthesis and subsequent heat treatment to prepare bismuth doped titanium dioxide nanofibers (Bi-doped TiO2 NFs). At first, we adopt Bi-doped TiO2 NFs as the working electrode to further study in DSSCs. Serving as working electrode, Bi-doped TiO2 NFs can remarkably improve open-circuit voltage (VOC). The VOC was significantly enhanced from 0.633 V to 0.800 V compared with pristine TiO2 does. However, this leads to a smaller JSC and a poorer overall performance for such devices. In order to improve the performance of DSSCs, we adopt Bi-doped TiO2 NFs as the scattering layer of DSSCs, and various thicknesses of meso-TiO2 nanoparticles (meso-TiO2 NPs) were used as working electrode to increase the short-circuit current (JSC). The incorporated Bi-doped TiO2 NFs can help the electron transport and may reduce the possibility for electron-hole recombination. After optimizing the device's parameter, the overall performance of the meso-TiO2 NPs/Bi-doped TiO2 NFs devices was dominated by JSC until a maximum efficiency was attained with a meso-TiO2 NPs thickness of 12 μm. Such optimized DSSCs exhibited high open circuit voltage of 0.787 V, high fill factor of 78.2%, and high power conversion efficiency of 8.89%.