Enhanced Efficiency in Dye-Sensitized Solar Cells by Electron Transport and Light Scattering on Freestanding TiO2 Nanotube Arrays

Dye-sensitized solar cells (DSSCs) were fabricated with closed- or open-ended freestanding TiO2 nanotube arrays as photoelectrodes that were decorated with carbon materials and large TiO2 nanoparticles (NPs) to enhance energy conversion efficiency. The energy conversion efficiency of DSSCs based on open-ended freestanding TiO2 nanotube arrays increased from 4.47% to 5.39%, compared to the DSSCs based on closed-ended freestanding TiO2 nanotube arrays. In DSSCs based on the open-ended freestanding TiO2 nanotube arrays, the energy conversion efficiency with carbon materials increased from 5.39% to 6.19% due to better electron transport, and that with a scattering layer from 5.39% to 6.24% due to more light harvesting compared to the DSSCs without carbon materials or scattering layer. Moreover, the energy conversion efficiency of DSSCs based on the open-ended freestanding TiO2 nanotube arrays with both carbon materials and scattering layer increased from 5.39% to 6.98%, which is an enhancement of 29.50%. In DSSCs based on the TiO2 nanotube arrays, the carbon materials can improve electron transport by π-π conjugation, and the large TiO2 NPs can enhance the capacity to light-harvest by scattering