Preparation and characterization of sol-gel derived copper-strontium-oxide thin films

P-type transparent conductive oxides have potential applications in photovoltaics, transparent electronics, and organic optoelectronics. In this paper, results are presented on the synthesis of Cu2SrO2 thin films, a p-type transparent conducting oxide by a sol-gel route. Cu(II)methoxide and Sr-metal dissolved in anhydrous isopropanol were used as precursor for the sol preparation. For potassium (K) doping, K-acetate dissolved in anhydrous isopropanol was used as the precursor. Films were spin-coated onto substrates and partially pyrolysed in air at 225deg. C. After partial pyrolization, a two stage annealing sequence was used to achieve the final film microstructure and composition. Although combinations of oxygen pressure, annealing time, and annealing temperature were used to obtain phase pure Cu2SrO2 thin films, X-ray diffraction consistently showed the presence of Cu2O as a second phase with Cu2SrO2-the desired phase. Microstructural studies showed similar phase separation in the films and confirmed the microcrystalline nature. The best conductivities obtained for the undoped and 1% K-doped films were 2 x 10-3 and 1.2 x 10-2 S/cm, respectively. Both films showed a broad optical absorption edge in the visible range