Control of tin oxide film morphology by addition of hydrocarbons to the chemical vapour deposition process H.M. Yates a, ⁎, P. Evans a , D.W. Sheel a , Z. Remes b , M. Vanecek b a Engineering and Physical Sciences, University of Salford, Manchester, M5 4WT, UK b Institute of Physics of the ASCR, v. v. i. Cukrovarnicka 10, CZ-162 00 Praha 6, Czech Republic abstract article info Article history: Received 26 March 2010 Received in revised form 17 September 2010 Accepted 20 September 2010 Available online 29 September 2010 Keywords: Tin oxide Chemical vapour deposition Morphology Alcohol In this paper we have shown that it is possible to modify and control the surface morphology of doped SnO 2 transparent conducting oxide thin films deposited by atmospheric pressure chemical vapour deposition by use of additives during the deposition process. A range of volatile organic compounds were explored, which caused changes of differing magnitude to the growth rates, crystallographic preferences, size and shape of the surface features and optical transmittance. Of the additives tested methanol and tertiary butanol were found to have the most significant influence allowing the surface to be modified from small, round features to much more elongated, sharp, pyramidal features. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Transparent conductive oxide (TCO) films are widely used in many consumer products with applications in flat screen high-definition televisions, computer screens, low emissivity and electrochromic windows [1], within thin film photovoltaic (PV) cells [2] and a wide range of other display type devices [3–5]. Surface morphology is an important property in transparent conducting oxides, which can critically affect the efficiency of the application. TCO's are used for both low emissivity coatings (low scatter required) and for photo- voltaic applications where surface control can be used to improve the light scattering properties of the front electrical contact on thin film solar cells and hence improve the efficiency of the cells. One of the dominant materials is F-doped SnO 2 which is extensively used for low emissivity windows (e.g. K Glass TM [6]), deposited inline by a chemical vapour deposition process. For this process, the optimum film is highly transparent, has low visible light scattering, low resistivity and low emissivity (0.16). For a different industrial area, for example, the thin film PV area (especially a-Si based), the exact specifications for the TCO will be different. A key objective for the PV industry is to further reduce the cost per unit of energy generated. This can be achieved both by reducing the manufacturing costs—where atmospheric pressure chemical vapour deposition (APCVD) has major potential and by increasing the efficiency of the PV cell. Transparent conducting oxide films have a key role in optimising efficiency, particularly in enhancing the light collection performance of cells, whilst using the minimum amount of absorber material. For TCO films to maximise (thin film) solar cell conversion efficiency, they must satisfy three conditions: advanced light trapping [7], high transparency and low resistance (10 Ω/sq). All three properties are linked via TCO film structure and composition, so optimisation of performance requires a careful compromise. For example, increased thickness, would increase surface roughness and generally enhance total scattering of incident light (by changing, shaping or sizing of features), but would also reduce the transparency and more importantly increase the optical absorbance of the TCO and hence lead to less light reaching the active part of the solar cell and detract from the overall efficiency. It has been previously shown that reducing the optical losses in the TCO is a decisive factor for ultimate efficiency due to light trapping [8,9]. In this paper we focus on producing thin films with specific morphologies that would have the potential to improve the light absorption in the active absorber layers and hence efficiency of thin film PV cells. For this application the TCO acts as the front electrical contact in the cell and has been previously found to be critical to the efficiency of the final solar cell [10]. As previously described, the film must be of high optical transparency and relatively low resistivity. In addition, an ability to control the surface roughness and feature shape would be highly advantageous, by influencing the amount of light reaching the absorber layers by introducing a transition layer, which acts similarly to a graded refractive index layer and thereby reduces the reflection losses at the TCO interface. A further effect of increasing surface roughness is the enhancement of light scattering, leading to “light trapping” as a result of total internal reflections, which leads to enhanced absorption within the active part of the cell. Increased Thin Solid Films 519 (2010) 1334–1340 ⁎ Corresponding author. Tel.: + 44 161 295 3115; fax: + 44 161 295 5111. E-mail address: H.M.Yates@salford.ac.uk (H.M. Yates). 0040-6090/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2010.09.037 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf