Fabrication of a double layered FTO/AZO film structure having enhanced thermal, electrical and optical properties, as a substitute for ITO films

Abstract

An ideal transparent conducting oxide (TCO) should possess high optical transparency and electrical conductivity along with good chemical and thermal stabilities while it is subjected to high temperature processes. In the present study, a novel TCO film which possesses good figure of merit (ϕ) (i.e. good optical transparency and electrical conductivity) along with good chemical and thermal stabilities and especially which can acts as a substitute for ITO has been realized. To achieve the combined unique characteristics of ZnO (thermal stability) and SnO2 (chemical stability), a double layered structure which consists of fluorine doped tin oxide (FTO) as the top layer on AZO layer, has been deposited using a simplified spray pyrolysis technique. In order to optimize the thickness proportions of FTO/AZO double layer for obtaining improved quality factors, five sets of samples were fabricated with different thickness proportions (1:5, 1:2, 1:1, 2:1 and 5:1) of AZO and FTO layers. Then, for the better understanding of physical properties of FTO/AZO double layered films, structural, optical and electrical studies were carried out and the results are reported. The minimum electrical resistivity of 9.141×10−3Ωcm with 80 % of optical transparency obtained for the FTO/AZO bilayer film having 5:1 thickness proportion, prompts us to conclude that this thickness proportion is suitable to achieve improved quality factor (1.185×10−3 (Ω/□)−1). The quality factor is found to be increased nearly four times after annealing (3.965×10−3 (Ω/□)−1).