Novel triple-layered photoanodes based on TiO2 nanoparticles, TiO2 nanotubes, and β-NaYF4:Er3+,Yb3+@SiO2@TiO2 for highly efficient dye-sensitized solar cells

Based on TiO2 nanoparticles (TNPs), open-ended TiO2 nanotube arrays (TNTs), and highly uniform double shell beta-NaYF4:Er3+, Yb3+@SiO2@TiO2 submicron-sized plates (NYFEY@S@T), novel triple-layered photo anodes were developed for highly efficient dye-sensitized solar cells (DSSCs). For triple-layered photoanodes, 0-D TNPs were grown as a first layer on fluorine-doped tin oxide (PTO) glass substrate with the thickness of 6 mu m to create a good contact and high specific surface area for loading the greater amount of dyes. To improve the dye-sensitized solar cells (DSSCs) efficiency, the 1-D TNTs were deposited as a second layer with five different thicknesses (9, 14, 24, 32, and 46 pm) due to their favorable electron transport rate. However, the photoelectric conversion efficiency of TNPs and TNTs layers is still low because of inefficiency of scattering and upconverting. Further, the 2-D NYFEY@S@T/TNPs (85% TNPs+15% NYFEY@S@T was also deposited onto the top surface of the TNTs film as a scattering and upconverting layer with the thickness of 7 mu m. The short-circuit current density (Jsc) of 17.47 mA cm(-2) and an efficiency (n) of 9.11% were achieved for the DSSCs with TNPs/TNTs/ NYFEY@S@T-TNPs photoanode with the TNTs layer thickness of 24 mu m and NYFEY@S@T content of 15 wt%, which were increased significantly by 38.1% and 16.6% in comparison with that of the DSSCs with single TNPs and bilayer TNPs/TNTs photoanodes. The obtained results indicated that significant enhancement in the performance of the DSSCs with TNPs/TNTs/NYFEY@S@T-TNPs photoanode is attributed to the peculiar triple-layered structure allowing the loading of more dye molecules, good light scattering and upconverting, and longer electron lifetime.