Solar Energy Materials & Solar Cells 91 (2007) 174–179 Crystalline silicon surface passivation by amorphous silicon carbide films M. Vetter à , I. Martı´n, R. Ferre, M. Garı´n, R. Alcubilla Department Enginyeria Electronica, Universitat Politecnica de Catalunya, C/ Jordi Girona 1-3, E-08034 Barcelona, Spain Received 13 February 2006; accepted 15 August 2006 Available online 2 October 2006 Abstract This article reviews the surface passivation of n- and p-type crystalline silicon by hydrogenated amorphous silicon carbide films, which provide surface recombination velocities in the range of 10 cm s 1 . Films are deposited by plasma-enhanced chemical vapor deposition from a silane/methane plasma. We determine the passivation quality measuring the injection level (Dn)-dependent lifetime (t eff (Dn)) by the quasi-steady-state photoconductance technique. We analyze the experimental t eff (Dn)-curves using a physical model based on an insulator/semiconductor structure and an automatic fitting routine to calculate physical parameters like the fundamental recombination velocities of electrons and holes and the fixed charge created in the film. In this way, we get a deeper insight into the effect of the deposition temperature, the gas flow ratio, the doping density of the substrate and the film thickness on surface passivation quality. r 2006 Elsevier B.V. All rights reserved. Keywords: Crystalline silicon; Amorphous silicon carbide; Passivation; Lifetime 1. Introduction In research-level crystalline silicon (c-Si) solar cells electronic surface passivation has been recognized as a crucial issue to achieve high conversion efficiencies. Improvements in this field have opened the door to enhance conversion efficiency up to date’s world record of 24.7% [1] under 1 sun illumination. Up to now, it has not been necessary to apply all the acquired knowledge about c-Si surface passivation to commercial c-Si solar cells. In this case and for cost reasons, the initial silicon material is low quality with a high amount of impurities and/or crystal defects. Hence, commercial c-Si solar cells are typically limited by bulk recombination. However, driven by the strong increase of the photovoltaic market in the last years and the limited availability of silicon from the feedstock of the electronic industry, solar cell manufactures are compelled to use the silicon material more economic- ally. Therefore, thickness reduction of the initial silicon wafer appears to be a straightforward and technologically feasible way for substantial material savings. Importantly, it has been demonstrated that conversion efficiencies beyond 20% can be achieved with thicknesses lower than 80 mm [2]. Collection efficiency of the photogenerated carriers in such thin devices is controlled by the back surface recombination rate as demonstrated by many theoretical studies [3]. A definitive solution to passivate the back surface is still not established. The most effective way to passivate the silicon surface is the growth of a thermal oxide at high temperatures (E1000 1C), which is used for high-efficiency laboratory solar cells. However, this method is for cost reasons not applicable in industrial processes. Silicon nitride (SiN x ) deposited by plasma-enhanced chemical vapor deposition (PECVD) seems to have certain advan- tage, since its properties are suitable for photovoltaic applications [4]. Apart from this, among all the available solutions for c-Si surface passivation, amorphous semi- conductors deposited by PECVD at low temperature (p400 1C) have revealed excellent surface passivation quality [5,6]. The c-Si surface passivating properties of hydrogenated amorphous silicon carbide films (a-SiC x :H) have been ARTICLE IN PRESS www.elsevier.com/locate/solmat 0927-0248/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.solmat.2006.08.004 à Corresponding author. Tel.: +34 93 401 7488; fax: +34 93 401 6756. E-mail address: mvetter@eel.upc.edu (M. Vetter).