Influence of Different Solvents on the Formation of Uniform Titanium Dioxide (TiO₂) Thin Film by Sol-Gel

Abstract

Abstract. Uniform Titanium dioxide (TiO 2 ) thin film is essential for application in high performance solar cells. A low cost approach using TiO 2 nanopowder extracted from tin mining waste to deposit TiO 2 thin films is demonstrated in this paper. Furthermore, the influence of different solvents (ethanol, acetone, isopropanol and ethylene glycol) on the formation of uniform TiO 2 thin films in sol-gel technique is studied. The films were characterized by an atomic force microscope (AFM), ultra violet -visible spectrometer (UV-Vis) and a current-voltage (I-V) measurement system. The correlations of the structural, optical and electrical behavior to the type of solvent used were discussed in details. IntroductionTitanium dioxide (TiO 2 ) or known as titania is a unique IV-VI semiconductor where it has three different polymorps. The naturally occurring polymorph is brookite and extremely difficult to synthesize. While the most commonly researched polymorphs are anatase and rutile. When the sintering temperature is over 500°C, brookite will transform to anatase form [1]. The anatase will transform to rutile when the temperature is over 600°C [2]. Anatase is proven recently as the most photocatalytically active and more ionic of the three polymorphs. In addition, the conduction band is better around 0.3 eV more positive than rutile phase [3].In practical technological applications, anatase TiO 2 is widely used for light emitting diodes, laser diodes and solar cells [4]. It shows magnificent performance when combined with organic dye in dye-sensitized solar cells (DSCs) which demonstrated by Gratzel [5][6]. On the other hand, the emerging of organic solar cells also requires TiO 2 nanolayer to improve the solar cell performance [7]. TiO 2 films also reported to have possibility to reduce air pollution when it absorbed carbon monoxide (CO) when coat on buildings [8]. There are several more reports have been found on the relevance of TiO 2 for the application of high technological devices. Therefore, it is essential to study the process of synthesizing TiO 2 thin films to improve the performance and to reduce the processing cost for manufacturing.There are several methods to synthesize TiO 2 thin films such as r.f. sputtering [9], laser ablation [10] and chemical vapor deposition (CVD) [11]. However, these methods require expensive and sophisticated equipments where not only the return of investment (ROI) is longer, the mass production also will be an issue. Sol-gel spin coating is a cost effective method and capable for mass production [12]. In this paper, nano-TiO 2 powder which was synthesized from local tin mining waste has been used as the starting material. Our initial works has been reported by M.Z. Sahdan et al. [13] demonstrating the effects of mass concentration and catalyst volume on the uniformity and performance of the TiO 2 thin films. In this study, different solvents have been used to synthesize