Cu modified ZnO nanoflowers as photoanode material for highly efficient dye sensitized solar cells

Abstract

The Cu-modified ZnO nanoflowers as photoanode material for dye sensitized solar cells are synthesized via a cetylmethylammonium bromide-assisted hydrothermal method. The main phase of the synthesized samples well matches the wurtzite type phase of ZnO. And the pure phase of Cu begins to appear and strengthen when the modified-Cu content excesses 1 wt%, indicating that Cu element not only dope into the lattice of ZnO but also cover on its surfaces. It is found that the morphologies of the ZnO samples can be tuned by the change of the modified-Cu content, from irregular nanoplates to cross-linked multileveled porous nanoflowers with a various Cu concentration of 0.5 wt%, 1 wt%, 1.5 wt% and 2 wt%, which further facilitate the dye adsorption and light-scattering. The photocurrent-voltage characteristics and electrochemical impedance spectroscopy are conducted to estimate the electrochemical properties of these solar cells with different Cu modification contents. Compared to the dye-sensitized solar cells with pure ZnO electrode, all the dye-sensitized solar cells with Cu-modified ZnO photoelectrodes present higher photovoltaic performance. The introduction of Cu into ZnO significantly enhances electron transport and retards charge recombination in the ZnO-dye interfaces, which induce the 84% improvement of short-circuit current density and 1.6 times enhancement of the power conversion efficiency for the dye-sensitized solar cells with 1.5 wt% Cu-modified ZnO photoelectrodes.