Resumen de Solution Growth and Functional Properties of Vertically Aligned ZnO Nanowires
Jiandong Fan
This dissertation has focused on three main topics: (1) Synthesis and characterization of ZnO:Cl NWs; (2) Hetero and homo nanostructures based on ZnO:Cl NWs for efficient PEC cells; (3) Photovoltaic performance of DSCs based on ZnO NWs. (1) Vertically aligned single-crystal and chlorine-doped ZnO NWs can be grown by a low-cost, high-yield and seed-free electrochemical route with controlled morphology, structural and optoelectronic properties. The carrier concentration of such ZnO:Cl NWs could be tuned in the range between 5× 1017 and 4×1020 cm-3 by varying the Cl doping concentration. Besides, intrinsic ZnO NWs with various lengths of 6-12 ?m and diameters of 40-120 nm can also be obtained by hydrothermal deposition for the application in DSCs. (2) Vertically aligned core@shell ZnO:Cl@ZnO homostructures and ZnO:Cl@ZnS and ZnO:Cl@TiO2 heterostructures NWs can be obtained by electrodeposition and/or SILAR two-step process. The PEC properties of these NWs can be highly enhanced up to a factor 5 with the presence of these shell layers. The enhancement factor depends on the shell thickness. These performances are associated with the improvement of the photogenerated charge carrier separation and surface to neutral inner part transfer capability achieved when increasing the space charge area within the NWs with a built-in electric field introduced by the doping profile. (3) We have employed [Co(bpy)3]2+/3+ redox couple as electrolyte in ZnO NWs-based DSCs. A direct comparison of the performance of [Co(bpy)3]2+/3+ and I?/I3? redox couples demonstrated the higher suitability of the cobalt complex, both in terms of a significantly improved Voc (Delta/Voc~200 mV) and a increased photocurrent (Delta/Jsc ~10%). The post-annealing of the NWs in argon allowed further improving the power conversion efficiency with a value of 30% compared to air. The improved efficiency was dominated by significantly higher photocurrents (Delta/Jsc~50%) measured from Ar-DSCs when compared with Air-DSCs.
