Introduction

The transparent conducting oxide (TCO) coated glass substrates are widely used as front electrode in thin film Photovoltaic (PV) solar cells. The TCO film is deposited by Chemical Vapour Deposition (CVD) technique using various liquid chemicals namely water (H2O), methanol (CH3COOH), Hydrofluoric acid (HF), Tin Tetrachloride (SnCl4) etc. All these chemicals are vaporized using non-openable SS bubblers (sealed through welding joints). Quite often, it is observed that during the deposition process of TCO film, the Tin tetrachloride (SnCl4) bubbler get chocked inside due to formation of particulate material at the outlet of bubbler and as well as at the diffuser bulb. In addition to this, various pipe joints that are welded on the top of the bubbler, also get corroded over a period of time and start leaking. As the bubbler is a sealed container, it is virtually impossible to remove the particulate material form the bubbler. Especially during the process, if the bubbler gets chocked, the process gets interrupted. To clean the bubbler, expensive SnCl4 liquid has to be drained out through SS tubes to glass bottles by pressurizing the bubbler. This is a cumbersome exercise. Invariably some vapours do come out and cause corrosion, as SnCl4 spontaneously reacts with air and produces HCl vapours. These HCl vapours attack all the SS pipelines carrying other process gases and their associated heater assemblies, the SS valves, thin-walled bellows and even the metallic portions of the mass flow controllers which get corroded over a period of time and become useless. This causes loss of time and money. To circumvent this problem, a new bubbler has been designed without welding any SS pipe to the metal flange and sealing with viton ‘O’ ring has been provided between the two SS flanges. Acid resistant PFA (perfluoroalkoxy) valves have been used in place of SS valves. One PFA pipefitting has been suitab- - ly modified for fixing and sealing the new improved diffuser bulb and tube made of Teflon material. Objective of the present work is to design a weld free, openable SS bubbler sealed with ‘O’ ring, with corrosion free Teflon tubing & PFA valves, compatible for various corrosive liquids at temperatures less than 100°C, for trouble free operation.