Electrochemical Etching of Fluorine-Doped Tin Oxide (FTO): Effects on Morphological, Electrical, Physical and Optical Properties

Abstract

In this study, the effect of electrochemical etching time on the layer thickness, electrical, optical, and physical properties of fluorine-doped tin oxide (FTO) films are reported. The electrochemical etching was carried out for various durations, up to 40 min, using an electrolyte composed of zinc acetate dihydrate dissolved in hydrochloric acid. The etching kinetics, which are defined by the gradual decrease in layer thickness, were thoroughly examined and correlated to the material’s electrical, optical, and wetting properties as well as surface chemistry. Surface passivation progressively impedes FTO dissolution, causing the etching rate to decrease exponentially. During the first 5 min of FTO etching, the sheet resistivity and surface energy increased from 13.2 to 109.0 Ω/□ and from 27.4 to 29.3 mN/m, respectively, accompanied by a gradual increase in charge-transfer resistance. This indicates the need of an optimized etching time that balances electrical, optical, and surface properties. A detailed analysis of FTO’s optical characteristics at various etching periods was conducted. The gradual alterations in the FTO surface chemistry and surface-related characteristics that were dependent on the etching time were primarily responsible for the observed changes in the physical, electrical, wetting, and optical properties. Additionally, a stronger surface-related influence on the charge carrier dynamics and recombination in the perovskite layer was demonstrated by the exponential decline in photoluminescence intensity of the MAPbI 3 films on the etched FTO substrates with increasing etching time. This study provides a deeper understanding of the electrochemical etching of FTO and highlights the potential for enhancing its structural, electrical, and wetting properties to improve performance in optoelectronic devices.