Ag Nanoparticle-Functionalized Open-Ended Freestanding TiO2 Nanotube Arrays with a Scattering Layer for Improved Energy Conversion Efficiency in Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) were fabricated using open-ended freestanding TiO2 nanotube arrays functionalized with Ag nanoparticles (NPs) in the channel to create a plasmonic effect, and then coated with large TiO2 NPs to create a scattering effect in order to improve energy conversion efficiency. Compared to closed-ended freestanding TiO2 nanotube array-based DSSCs without Ag or large TiO2 NPs, the energy conversion efficiency of closed-ended DSSCs improved by 9.21% (actual efficiency, from 5.86% to 6.40%) with Ag NPs, 6.48% (actual efficiency, from 5.86% to 6.24%) with TiO2 NPs, and 14.50% (actual efficiency, from 5.86% to 6.71%) with both Ag NPs and TiO2 NPs. By introducing Ag NPs and/or large TiO2 NPs to open-ended freestanding TiO2 nanotube array-based DSSCs, the energy conversion efficiency was improved by 9.15% (actual efficiency, from 6.12% to 6.68%) with Ag NPs and 8.17% (actual efficiency, from 6.12% to 6.62%) with TiO2 NPs, and by 15.20% (actual efficiency, from 6.12% to 7.05%) with both Ag NPs and TiO2 NPs. Moreover, compared to closed-ended freestanding TiO2 nanotube arrays, the energy conversion efficiency of open-ended freestanding TiO2 nanotube arrays increased from 6.71% to 7.05%. We demonstrate that each component-Ag NPs, TiO2 NPs, and open-ended freestanding TiO2 nanotube arrays-enhanced the energy conversion efficiency, and the use of a combination of all components in DSSCs resulted in the highest energy conversion efficiency.