Nanocrystalline proprieties of TiO2 thin film deposited by ultrasonic spray pulverization as an anti-reflection coating for solar cells applications

Abstract

Abstract Titanium oxide (TiO2) films have been synthesized on quartz, silicon and textured silicon substrates by chemical ultrasonic spray deposition. The textured silicon substrate was carried out using Na2CO3 solution. The sample surface exhibits uniform pyramids with an average height of 5 µm. In this paper, particular attention is given to the TiO2 films prepared by spray ultrasonic system using Tetra iso-Propoxide Orthotitanate Titanium (TPOT) as a precursor. The solutions were sprayed onto substrates heated at various temperatures 350 - 550 °C. The properties of films as a function of temperature parameter were investigated using structural and optical analysis. According to XRD, FTIR and Micro-Raman spectroscopies, the anatase phase was found and exhibits nanograins of 9 to 15 nm in size. The indirect and direct bad gap were found to increase by increasing substrate temperature due to the decreasing of nanograins size and were estimated to be around 3.28 and 3.38 eV. A transmittance higher than 80% was found. This paper reports on anti-reflection coating application of TiO2 layers due to its good transparency and appropriate refractive index varies between 2.19 - 2.40 at λ = 632.8 nm as a function of temperature determined by UVVisNIR spectrophotometer and Ellipsometry. To achieve optimum anti-reflection characteristics different anti-reflection designs were experimentally examined with polished and textured substrates. The average reflectance of the polished silicon used in this study is 39%, with TiO2 it decreases to 9%. The textured surface reduces the average reflectance of silicon to be around 14% and it decreases dramatically to 5% after deposition of a single layer of TiO2 as an anti-reflection coating. The gain in density of the short-circuit photocurrent assigned to the reduction of reflection losses up to 44% and 58% were predicted with TiO2 single-coating in polished and textured silicon substrates respectively.