ELSEVIER Solar Energy Materials and Solar Cells 41/42 (1996) 485-492 sol~ E n ~ IVlatmats and ~ r Solution of the ZnO/p contact problem in a-Si:H solar cells M. Kubon, E. Boehmer, F. Siebke, B. Rech, C. Beneking, H. Wagner Forschungszentrum Jiilich GmbH, ISI-PI~, D-52425 Jiilich, Germany Abstract This paper addresses the problem of preparing a good p-layer contact with zinc oxide as TCO. Our approach was to deposit pin cells with different p-layer recipes on ZnO coated SnO2:F and on uncoated SnO2:F in one run, in order to obtain a direct comparison of the interface properties of the two TCO materials under the condition of as equal as possible surface morphology. The pin cells prepared on the ZnO surface exhibit a lower fill factor (FF). Our experiments demonstrate that the hydrogen interaction with the ZnO surface plays the most decisive role for the ZnO/p contact. We explain the observed effects using a band diagram of the ZnO/p interface and show that the accumulation layer at the ZnO surface -- caused by atomic hydrogen in the plasma -- is responsible for the low FF in pin cells. Based on this model the contact problem is solved by introducing a/xc-n-Si intralayer between ZnO and p-layer resulting in an identical high FF on both ZnO and SnO 2 substrates. 1. Introduction In order to obtain further improvement in stabilized efficiency of a-Si:H solar cells, growing attention is being paid to the transparent conductive oxide (TCO) material that forms the front electrode. Especially the TCO/p contact properties and their influence on solar cell parameters have been the object of a number of investigations. Fluorine doped SnO 2 is a well known material for TCO films, exhibiting favourable surface textures which enhance the conversion efficiency. However, SnO 2 is reduced during the early stages of solar cell deposition, leading to additional absorption [1]. In contrast, aluminum or boron doped ZnO shows higher transparency in the visible range and higher plasma stability [2], but ZnO/p contact problems have been reported [3]. Especially free hydrogen in the plasma has a negative influence on the ZnO surface [4]. 092%0248/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved SSD1 0927-0248(95)00126-3