A dual-functional double-layer film with indium-doped ZnO nanosheets/nanoparticles structured photoanodes for dye-sensitized solar cells

Abstract

A double-layer film composed of an upper-layer of indium-doped ZnO (IZO) nanosheets and a lower-layer of IZO nanoparticles structure (designated as DL-NS,s/NP,s:IZO) has been successfully synthesized by a simple two step electrospray method and studied as the dye-sensitized solar-cell (DSSCs) electrodes with the aim of developing a cost-effective alternative fabrication method and improving the performance of ZnO-based DSSCs. The XRD patterns demonstrated that the films exhibited the hexagonal wurtzite structure with preferential orientation along the (0 0 2) crystal plane and all the peaks slightly shifted toward the larger angle side due to the indium (In) doping. The composition of the doped ZnO films was confirmed with the help of X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS) and X-ray photospectroscopy (XPS). The upper-layer made of upright-standing IZO nanosheets (NS,s:IZO) acts as scattering centers to utilize more light as well as the direct pathway for the electrons to move towards the electrodes. The lower-layer composed of nonporous IZO nanoparticles increases the dye adsorption and also allowed for the suppression of the recombination of injected electrons. It was found that the DL-NS,s/NP,s:IZO film could significantly improve the efficiency (6.9%) of DSSCs owing to its enhanced light-scattering capability as well as intrinsic components of films, the photon-to-electron transfer process of the cells and relatively high surface area. This efficiency was significantly improved over the 4.8% obtained for double light-scattering-layer with DL-NS,s/NP,s:ZnO film and was also higher than the 3.2% achieved for single-layer of NP,s-IZO film. The fabricated cells showed highly durable cell performance, even after 40 days under atmospheric conditions. The efficiency achieved for the best DSSCs in this work is the highest ever reported value for a double light-scattering-layer ZnO film-based DSSCs.