High efficiency dye-sensitized solar cells based on the ZnO nanoparticle aggregation sphere

Abstract

Sub-micrometer-sized ZnO spheres have been prepared from methanolic zinc acetate dihydrate solution through the aggregation of ZnO nanocrystallites. The ZnO nanocrystallites were aggregated through the hydrolysis reaction of the zinc hydroxide complex due to the decrease of the surface free energy in the precursor solution, finally constructing a hierarchical ZnO nanoparticle aggregation sphere (NAS). Since the ZnO NAS is consisted of the ZnO nanocrystallites and are submicrometer-sized, it is function as efficient light scatters while the nanocrystallites provide the high internal surface area for the dye molecule adsorption in the dye sensitized solar cells (DSSC). The ZnO NAS is quite different from general ZnO colloidal nanocrystal clusters (CNC) in that the structure of ZnO NAS, due to the interconnected nanoparticles, can allow more efficient electron transport and charge collection through a designed path in the solar cell. Owing to the favorable charge collection, long charge diffusion length, and long electron life time, DSSC based on ZnO NAS showed photocurrent density (Jsc) and fill factor (FF) higher than that of ZnO CNC; also, an overall power conversion efficiency of 6.01% was obtained, which represented a remarkable increase compared to that of ZnO CNC (η = 4.59%) which had a similar film thickness.