Tin dioxide thin films deposited by sol – gel technique

Wide band gap metal oxide semiconductors are an important material base in optoelectronic industry. Dye sensitized solar cells and especially the organometallic perovskite ones present a new way of application of these materials with specific requirements for their properties. Therefore the reduction of production costs in relation to the efficiency is an important factor for its commercialization. In this work we present sol-gel approach to form dense, uniform and voids free electron selective layers of intrinsic SnO₂ for application in nano-sized organometallic photovoltaics. The purpose is to find conditions for deposition at lowest temperatures of compact and well crystallized SnO₂ thin films with effective electron blocking ability with perspective to apply on polymer substrates. The process of pyrolysis of the precursors into expected SnO₂ was investigated by Differential Scanning Calorimetry. The results were used to have an insight for main reaction steps and to define an adequate annealing regime. The films were characterized by X – ray – photoelectron spectroscopy XPS, diffractometry, UV – Vis spectrophotometry and Scanning Electron Microscopy. Different solvents for the precursor SnCl₄.5H₂O were investigated in order to minimize their influence onto polymeric substrates. In the row between ethanol, methanol and isopropanol the last ones yielded compact layers without pinholes and cracks. The level of electrical leakage was estimated by cyclic voltammetry measurements of residual current in aqueous redox solution. The quality of the coverage depends on the concentration of the precursor solution but at over 0.5 M SnCl₄ the root mean squares (RMS) roughness of the films increases.