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.