Structural, optical, and electrical properties of p-type NiO films and composite TiO 2/NiO electrodes for solid-state dye-sensitized solar cells

Abstract

p-Type nickel oxide thin films were prepared by sol–gel method, and their structural, optical and electrical properties were investigated. The Ni(OH) 2 sol was formed from nickel (II) acetate tetrahydrate, Ni(CH 3COO) 2·4H 2O, in a mixture of alcohol solution and poly(ethylene glycol), and deposited on an ITO substrate by spin coating followed by different heat treatments in air (50–800 °C). The formation and composition of NiO thin film was justified by EDX analysis. It is found that the thickness of the NiO film calcined at 450 °C for 1 h is about 120 nm with average particle size of 22 nm, and high UV transparency (∼75%) in the visible region is also observed. However, the transmittance is negligible for thin films calcined at 800 °C and below 200 °C due to larger particle size and the amorphous characteristics, respectively. Moreover, the composite electrode comprising n-type TiO 2 and p-type NiO is fabricated. The current–voltage ( I– V) characteristics of the composite TiO 2/NiO electrode demonstrate significant p-type behavior by the shape of the rectifying curve in dark. The effect of calcination temperature on the rectification behavior is also discussed.