Chemical Purity of Chemically Sprayed Thin Films

Abstract

The influence of different experimental parameters to the chemical purity of thin films prepared by chemical spray process is studied. It is shown that the sprayed A 2 B 6 and CuInS 2 thin films contain different solid decomposition products in concentrations that depends on the substrate temperature and ratio of components in the initial solutions. IntroductionThe conversion of sunlight directly into electricity using the photovoltaic properties of materials is the most elegant alternative energy conversion process due to the immense solar energy resource. The limitations of solar energy practical use are high price of produced electricity due to the highly dispersed character of solar radiation, low efficiency and high price of solar cells materials and technologies. Therefore, research into photovoltaic alternatives is imperative to make the technology competitive. This includes the development of low-cost techniques, higher efficiency thin films cells that require less material. Spray pyrolysis method is a widely used process to produce large-area metal oxide and chalcogenide thin films and it seems attractive for depositing low cost films of ternary compounds, too. Large number of investigations are connected with sprayed ZnO, CIS and A 2 B 6 thin films for different applications [1][2][3][4][5][6][7][8][9][10][11] in which the dependence of film properties on the technological parameters has been studied. It is shown that the spray pyrolysis is very suitable to prepare metal oxide thin films due to no need for the use of inert atmospheres [1-3]. The influence of experimental parameters as growth temperature and doping with dopants is investigated with the goal to obtain thin metal oxide films with high optical transparency and electrical conductivity. The effect of the growth temperature on the structure of CIS type films prepared by spray pyrolysis is studied in papers [4][5][6]. The film growth temperature in the range of 300 -400 °C is usually used to deposit the films. It is shown, that the composition of the starting solution (Cu/In and S/Cu) has a strong effect to the composition and structure as well as on the properties of sprayed films [4][5] and that Cu/In ratio is higher in the films than that in starting solution, especially at growth temperatures higher than 400 °C [6]. Copper-rich solutions lead to highly textured films whereas crystal growth in the film is accelerated by presence of copper containing phases which segregate on the surface of the film [4][5]. At the same time there is no studies dealing with the effect of the composition of starting solutions and the spraying process parameters on the impurity concentration and chemical composition of the different films. This paper has the aim to represent our results in this field.Interface Controlled Materials. Edited by M. Rühle and H. Gleiter