Titanium Dioxide Nanotubes Decorated with Nanoparticles for Dye Sensitized Solar Cells
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Titanium Dioxide Nanotubes Decorated with Nanoparticles for Dye Sensitized Solar Cells Xuan Pan1, Yong Zhao1, Changhong Chen1,2, and Zhaoyang Fan1 1
Nano Tech Center and Dept. of Electrical and Computer Engineering, Texas Tech University, Lubbock, TX, United States. 2 Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, China. ABSTRACT
The titanium dioxide (TiO2) nanoparticle (NP) structure has higher surface area and dye loading value to increase photon absorption while the nanotube (NT) can suppress the random walk phenomena to enhance carrier collection. In this work, hydrothermal method was utilized to infiltrate the TiO2 nanotube array by TiO2 nanoparticles with the aim of combining the advantages of both nanostructures to improve dye sensitized solar cells (DSSCs) efficiency. Structure morphology, device performance, and electrochemical properties were investigated. SEM observation confirmed that around 10 nm TiO2 nanoparticles uniformly covered the NT wall. TiO2 NT samples at three different lengths: 8 μm, 13 μm and 20 μm, decorated with different amount of nanoparticles were studied to optimize the structure for light absorption and electron transport to achieve high solar conversion efficiency. Electrochemical impedance spectroscopy (EIS) was also employed to investigate the cells’ parameters: electron lifetime (τ), diffusion length (Ln) et al, to gain insight on the device performance. The incident photon conversion efficiency (IPCE) was also reported. INTRODUCTION Since the emergence of dye-sensitized mesoporous TiO2 solar cells [1, 2], it has received considerable attention as a potential alternative to conventional p-n junction solar cells, due to the features of cost effectiveness, exceptional stability and a commercially feasible efficiency. The efficiency of a DSSC can be enhanced by optimizing the TiO2 architecture, sensitizer, and electrolyte, and a good amount of efforts have been devoted in the arrangement of the nanocrystals. In a TiO2 nanoparticles (NPs) film [3], electrons perform random walks over this disordered framework leading to increased scattering and recombination at the surfaces and interfaces, thereby lowering electron collecting efficiency. To reduce the electron loss related with the random transport, TiO2 nanotubes (NTs) arrays, aligned parallel to the electroncollecting direction [4], were utilized to construct mesoporous films [5]. One of the significant advantages of NT-based DSSCs over NP-based cells is observably higher charge collection efficiencies owing to direct pathways for species (electrons, holes and ions) to be transported through the ordered tube walls or pores. However, highly ordered NTs has a relatively smaller surface area in comparison with compacted NPs, therefore leading to lower dye absorption and then a reduction of the light harvesting. Our work is focused on infiltrating the TiO2 NT arrays with TiO2 NPs so as to combine the merits of both structures and also studying the DSSC properties based on this mixe
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