Low temperature carving of ZnO nanorods into nanotubes for dye-sensitized solar cell application

• Large scale arrays of highly oriented ZnO NTs have been fabricated and investigated.
• The DSSCs made of these 2.5 μm NRs and NTs resulted in conversion efficiencies of 0.34% and 0.9%, respectively.
• EIS measurements have demonstrated that the NTs could acquire a higher electron lifetime compared to NRs.
• Twofold electron lifetime electron accompanied by half electron transport time for ZnO NTs compared to NRs.

High aspect ratio zinc oxide (ZnO) nanotubes (NT) were synthesized based on a two-steps approach. In the first step, ZnO nanorod (NR) arrays were prepared by chemical bath deposition from an aqueous of zinc nitrate. In the second step, the cores of ZnO NRs were carved selectively in a KCl solution, resulting in the formation of a tubular structure. The influence of KCL concentration, temperature, and immersion time on the ZnO NT formation process was completely characterized and investigated. 12.5 μm NRs and NTs have been utilized to manufacture dye-sensitized solar cells (DSSCs) and as a result, conversion efficiencies of 1.06% and 2.87% were obtained, respectively. Electrochemical impedance spectroscopy measurements have demonstrated that the NTs could acquire a higher electron lifetime compared to NRs which causes a faster electron collection. The overall improvement in NT-based DSSC performance demonstrates a new approach to enhance the efficiency of dye-sensitized solar cells.