Exploring the interplay of the water–methanol solvent admixture on the optoelectronic properties of spray pyrolyzed fluorine-doped tin oxide thin films and their potential use in solar cell fabrication

Abstract

Transparent conducting oxide thin films have attracted significant research attention owing to their potential applications in solar cells and other optoelectronic devices. Herein, the influence of solvent admixtures containing methanol (CH₃OH) and water (H₂O) in varying ratios on the optoelectronic characteristics of fluorine-doped tin oxide (FTO) thin films prepared by the spray pyrolysis method has been explored. Several analytical techniques were employed to understand the relationship of solvent composition with the structure, morphology, and topography of the grown FTO thin films. Scanning electron microscopy analysis showed a decrease in the thickness of the thin films from 8.2 μm for M0 (0 vol% CH₃OH) to 456 nm for M90 (90 vol% CH₃OH), which was attributed to the change in mist formation dynamics. The average transmittance (T) of FTO thin films in the visible range increased when the CH₃OH content was increased in the spraying solution due to the decreased thickness and Urbach energy and increased band gap. On increasing the CH₃OH content in the spraying solution, the sheet resistance (R_s) decreased due to increased carrier density and enhanced mobility. The best sample prepared (M90), with pyramidal surface morphology, showed promising T (400–800 nm) and R_s of 73% and 8 Ω □⁻¹, respectively. M90, exposed to harsh thermochemical conditions, i.e. 550 °C (3 h), 1 M H₂SO₄ (72 h), and 1 M KOH (72 h), retained its optoelectronic characteristics well. The figure of merit, determined by taking into account both T and R_s, was also found to be the highest for M90. To demonstrate the utility of the prepared FTO thin films in different optoelectronic devices, Cs_0.05(FA_0.92MA₀.₀₈)Pb(I_0.92Br₀.₀₈)₃ perovskite solar cells were prepared on M90 in an inverted configuration, and a power conversion efficiency of 14% was realized under standard AM 1.5G illumination. The series of prepared solar cells on M90 is on par with the other high-efficiency solar cells, demonstrating its superior electrical characteristics and reliability to be used for various applications.