Influence of ZnO/p + a-Si:H Microcrystallization and Antireflection Coatings on pin a-Si:H Solar Cells Performance
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Influence of ZnO/p+a-Si:H Microcrystallization and Antireflection Coatings on pin a-Si:H Solar Cells Performance Andrzej Kolodziej, Pawel Krewniak, Stanislaw Nowak Institute of Electronics, University of Mining and Metallurgy, al.Mickiewicza 30, 30-059 Kraków, Poland ABSTRACT In general terms this paper analyzes effectiveness of ZnO/p+/i a-Si:H/n+/Al solar cells made on commercial glass substrate with double-sided antireflection coatings. The primary topic, however, is the ZnO/p+/i a-Si:H junction based on layers obtained by the reactive magnetron sputtering (RMS) of Si:B, Si:P, Al, Zn:Al targets, where the “i” layer is a protocrystalline RFCVD layer. These single layers, as well as the respective structures, were studied using primarily Grazing Incidence X Ray Analyzes and AFM spectroscopy. In particular, the microcrystallization, surface roughness and chemical composition of the films were studied with respect to film thickness, RMS power and hydrogen dilution. The nature of the influence of ZnO/p+/i a-Si:H crystallization on pin a-Si:H solar cells performance is presented. Optical transmission and reflection measurements were used to measure the light flux reaching the “i” layer. We determined the experimentally observed angular distribution of scattered light in transmittance through glass/ZnO:Al/p+ silicon and double antireflection coatings on glass/ ZnO:Al/p+ silicon junctions. The optoelectronic properties of glass/ZnO/pin a-Si:H/Cr/Al cells are examined by systematic investigation of their I-V characteristics subsequent to steady-state conditions. INTRODUCTION Double-sided antireflection coatings have recently been taken under consideration by several different solar cell companies as components improving pin a-Si:H solar cell performance. The purpose of this article is to add further experimental results involving our solar cells made on glass substrates. The research described in the paper is intended to prepare the technological groundwork for ZnO/p+/i a-Si:H/n+ junctions, based on layers obtained by the reactive magnetron sputtering (RMS) of the Si:B, Si:P, Al, Zn:Al targets, where the “i” layer is a protocrystalline RFCVD layer [1-5]. There is a great uncertainty concerning the repeatability of the manufactured structures of solar cells. It is therefore extremely difficult to draw univocal conclusions. Accordingly, we repeatedly return to previously published experimental works and verify the results once again. In particular, recurrent problems with the deposition rate of a-Si:H layers by means of RFCVD and the utilization of B2H6 and PH3 inclined us to renew trials with the method of reactive magnetron sputtering (RMS) under conditions of higher pressure, regarding the front side and back side of the solar cell structure, i.e. glass/TCO/p+ a-Si:H and n+ a-Si:H/ZnO/Al. In the paper we attempt to answer the following questions: 1. Are there any advantages to be derived from using double-sided antireflection coatings? 2. Which of the structures obtained by means of RMS, ZnO/p+ or ITO/p+, better enhances
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