IMPROVED CHEMICAL BATH DEPOSITION OF CdS ON FTO COATED GLASS USING A PLASMA SURFACE PRE-TREATMENT F. Lisco 1* , K. Bass 1 , G.Claudio 1 , P. Kaminiski 1 , M Losurdo 2 , B Maniscalco 1 and J M Walls 1 1 CREST, School of Electronic, Electrical and Systems Engineering, Loughborough University, Loughborough, Leicestershire, LE11 3TU, UK; 2 Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR, via Orabona 4, 70126 Bari, Italy *Corresponding author: F.Lisco@lboro.ac.uk Abstract Thin film cadmium telluride (CdTe) photovoltaic technology is a financially viable alternative to crystalline silicon. Thin film CdTe devices are multi-layer systems deposited on glass in a superstrate configuration. A basic CdTe cell consists of a transparent conductive oxide (TCO) top layer, a thin Cadmium Sulphide (CdS) n-type window layer, a thick layer of p- type CdTe absorber and a metallic back contact. In this study, we report on way to improve the quality of a low cost wet chemical process to deposit the cadmium sulphide layer. We report preliminary results on the use of a novel plasma treatment process that increases the surface energy of the TCO coated glass and leads to pinhole free CdS using a chemical bath whose film thickness can be optimized to less than 100nm while maintaining continuity of the film. The plasma treatments were tested by using an Argon/Oxygen mixture in different ratios. The plasma treatment primarily results in increased film density and increased grain size. These conclusions are supported by optical, structural and chemical measurements. Introduction A basic CdTe cell consists of a transparent conductive top layer, a thin cadmium sulphide (CdS) n-type window layer, a thicker layer of p- type CdTe and a metallic back contact [1]. The aim of this work is to investigate the plasma treatment effect on the quality of CdS films grown by chemical bath deposition. The most common TCO used in thin film CdTe is a Fluorine doped tin oxide (TEC 10 or TEC 15 supplied by NSG-Pilkington). These TCO materials are rough enough to increase the light trapping effect on one side but on the other one this can increase the pinholes formation. Here we report on the use of a novel plasma treatment process on TEC15 substrates that from preliminary results increases the surface energy of the substrate and improve the pinhole free growth of CdS by using a chemical bath deposition (CBD). Experimental Different plasma gases were tested on the FTO coated glass substrate. The main parameters involved have been: gas composition, power and treatment time. The power and the time were kept constant respectively at 100W and 300 seconds, while gas composition varied. The process condition analysed were: • 20sccm Ar/30sccm O 2 • 50sccm Ar • 50sccm O 2 • 30sccm Ar/20sccm O 2 • 40sccm Ar/10sccm O 2 • 45sccm Ar/5sccm O 2 Water contact angle measurements, as indication of surface energy of the material, were performed on the surface straight after each treatment. The contact angle measurement used for testing surface cleanliness for both glass and semiconductors [2] reflects the surface energy, according to Young’s equation: . [6] (1) Hence, a surface with higher surface energy has lower contact angle.