High deposition rate of low resistive and transparent ZnO:Al on glass with an industrial moving belt APCVD reactor
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High deposition rate of low resistive and transparent ZnO:Al on glass with an industrial moving belt APCVD reactor
A. Illiberi1, B. Kniknie1, H.L.A.H. Steijvers1, D. Habets1, P.J.P.M. Simons1, E.H.A. Beckers1, J. van Deelen 1 Netherlands Organization for Applied Scientific Research (TNO), PO Box 6235, 5600 HE Eindhoven, The Netherlands *Corresponding author: [email protected] ABSTRACT Aluminum doped ZnOx (ZnOx:Al) films have been deposited on glass in an in-line industrialtype reactor by a metalorganic chemical vapor deposition process at atmospheric pressure. ZnOx:Al films can be grown at very high deposition rates of ~ 14 nm/s for a substrate speed from 150 mm/min to 500 mm/min. ZnOx:Al films are highly conductive (R < 9 Ohm/sq, for a film thickness above 1300 nm) and transparent in the visible range (> 80%). Amorphous silicon p-i-n solar cells have been grown on as deposited ZnOx:Al films, without optimizing the surface texturing of ZnOx:Al films to enhance light scattering. An initial efficiency of approximately 8% has been achieved. INTRODUCTION Doped zinc oxide (ZnO) films have received increasing interest in recent years since they combine the common properties of transparent conductive oxides (TCO), i.e. high conductivity and excellent transparency, with low cost, low toxicity, easy fabrication process and patterning [1,2]. In particular, doped ZnO has become a valid alternative to the commonly used indium tin oxide (ITO) as TCO layer for silicon thin-film solar cells, being highly stable in a hydrogen plasma environment [3-5]. Numerous methods for the deposition of ZnOx:Al films have been proposed, including: thermal chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition, magnetron sputtering, pulsed laser deposition, spray pyrolysis and sol-gel process [6-11]. For a large scale production of ZnOx:Al films, it is desirable to use a deposition process with high growth rate, which operates at atmospheric pressure and can be easily applied to continuous, in-line manufacturing [12,13]. In particular for solar cells applications, high deposition rate is important since high production throughputs are required for solar cells manufacturing to decrease the production costs. EXPERIMENTAL ZnOx:Al films have been deposited by using tertiary-butanol [(CH3)3COH, (t-BUT)] as oxidant for diethylzinc [Zn(C2H5)2, (DEZ)] and trimethylaluminium [Al(CH3)3, (TMA)] as dopant gas [14]. A schematic of the deposition set-up is shown in Fig. 1. The liquid precursors (DEZ, t-BUT and TMA) have been vaporized and injected separately into the deposition zone by using nitrogen as carrier gas. The injector is placed parallel to the substrate and it is composed by three different nozzles, one for each gas precursor. Two exhausts limit the deposition zone along the direction of the movable substrate. For the current work, ZnOx:Al
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films have been deposited on a glass substrate (Schott AF 32, 5 x 5 cm2), warmed up to a set temperature of 480°C and moving with a speed from 50 mm/min to 500 mm/min.
Figure 1. Sc
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