Preparation And Physical Properties Of CuO Films By Sol-gel Technique

CuO is p-type semiconductor with narrow band gap.CuO films are widely used in solar cells,gas sensors and photochemical cells.The sol-gel method is simple and easy to control the composition and microstructure of the film.Furthermore,the composition of precursor is the main factor affecting film formation and membrane structure.In this paper,different precursors were prepared by three different sources of copper(copper chloride dihydrate,copper acetate monohydrate,copper nitrate trihydrate).The sol-gel spin coating technique was used to prepare CuO thin films with different microstructure.The phase structure,surface morphology,optical and electrical properties were characterized and analyzed.The details are as follows.First,CuO thin films were prepared by the precursor prepared from copper chloride dihydrat(CuCl2·2H2O).CuO thin films were annealed at 500?,the preferred orientation growth of(111)/(200)was more obvious with the annealing time prolonged.After annealing,the CuO film has good crystal,compact morphology,good optical and electrical properties,which is suitable for the absorption layer of solar cells.In addition,it was found that Cl~-was one of the important factors to make the CuO films compact and well-crystallized.Second,copper acetate monohydrate(Cu(CH3COOH)2·H2O)was as the source of copper.Then a fast pyrolysis heat treatment method was adopted to heat CuO thin films.The prepared films were with porous morphology(similar to the wormhole).Otherwise,based on the previous conclusion about the introduction of Cl~-,Cl~-was introduced to the precursor to explore the changes of CuO film morphology.It was found when the monohydrate copper acetate precursor was prepared with introducing a small amount of Cl~-,the prepared CuO thin films obviously became compact from porous,and its particle size was significantly larger.Moreover,the preferred orientation growth changed,and its optical and electrical propertiy has become better.The effects of different pyrolysis temperatures on the crystallinity,morphology and optical and electrical properties of CuO films were also investigated.Third,the precursors were prepared with copper nitrate trihydrate(Cu(NO3)2·3H2O).It was found that the CuO films has new morphology which completely different from the foregoing.It was not compact like the CuO thin film prepared by copper chloride dihydrate,but the surface of the thin film was relatively flat.In this experiment,the effects of different pyrolysis temperatures on the properties of the films were investigated.Similarly,Cl~-was also introduced into the precursor.Under the same preparation conditions,the morphology changed significantly,and all the surface cracks in the original morphologies were"bridged".The films'surfaces became particularly uniform and compact,and the roughness of CuO thin films increased.The particles were larger with the transverse size of particles up to about 700nm.In general,based on sol-gel method,controlling the precursor components and adopting the heat treatment scheme of rapid pyrolysis and slow annealing,CuO films were prepared which have different morphologies.The CuO films are expected to be used in the field of optical electrical field.