Abstract
Granular ZnO nanostructures of single-crystalline wurtzite hexagonal phases were synthesized by a facile and low-cost chemical method in aqueous condition. The average size of ZnO nanograin increased with reflux time, and it significantly affected the open circuit potential(Voc)while the short circuit current density(Jsc)was not changed much. The overall energy conversion efficiency was 1.82% with the smaller grain size ofca.250 nm when it was used as photoelectrode of DSSCs. The positive shifting of the Fermi energy (EF) and low density of surface states (DOS) were consistent with the reduction of the recombination of excited electron with electrolyte for smaller grains.
Highlights
Zinc oxide (ZnO) is unique in exhibiting both semiconducting and piezoelectric properties [1]
It was partly because there was no exciton generation in Z1 nanograins during the operation of dye-sensitized solar cells (DSSCs) and the source of electron was from dyes, which were mostly excited by visible light under AM 1.5 condition
Crystalline ZnO nanograins being synthesized by a facile hydrothermal method in aqueous system were used as photoanodes in DSSCs
Summary
Zinc oxide (ZnO) is unique in exhibiting both semiconducting and piezoelectric properties [1]. The less population of deep traps in ZnO nanostructures compared with TiO2 nanoparticles induced the longer electron lifetime [2]. In spite of these superior physical properties of ZnO, the photoconversion efficiency of TiO2-based DSSC is generally much higher than ZnO. This was mainly attributed to the acidity of the binding groups of dyes (e.g., N719, N3, and black dyes, etc.), which reduced the chemical stability of ZnO by dissolving it to form a precipitation of dye-Zn2+. The effects of the size of ZnO nanograin on the photovoltaic performances of DSSCs were studied in conjunction with their morphology as well as the optical and the electronic properties
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