Uniformity and Quality of Monocrystalline Silicon Passivation by Thin Intrinsic Amorphous Silicon in a New Generation Pl
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rsUniformity and quality of monocrystalline silicon passivation by thin intrinsic amorphous silicon in a new generation plasma-enhanced chemical vapor deposition reactor B. Strahm1, Y. Andrault1, D. Bätzner1, D. Lachenal1, C. Guérin1, M. Kobas1, J. Mai2, B. Mendes1, T. Schulze2, G. Wahli1, A. Buechel1 1 Roth & Rau Switzerland SA, Rue de la Maladière 23, CH-2000 Neuchâtel, Switzerland. 2 Roth & Rau AG, An der Baumschule 6-8, D-09337 Hohenstein-Ernstthal, Germany. ABSTRACT This work reports the first results of a new generation plasma-enhanced chemical vapor deposition (PECVD) reactor manufactured by Roth and Rau. This large area parallel plate reactor has been especially designed for the manufacturing of silicon heterojunction solar cells which are made of very thin amorphous silicon films over monocrystalline silicon substrates. Layer thickness uniformity below ± 3 % is reported for both intrinsic and doped layer over a 400 x 400 mm2 area. Moreover, it is shown that the passivation quality is excellent with life-times up to 4.15 ms on n-type FZ silicon substrates. A ± 0.6 % uniformity in open circuit voltage (mean value of 701.4 mV) is achieved over 32 devices having a 4 cm2 area and an average conversion efficiency of 19.5 %. INTRODUCTION Silicon heterojunction technology (Si-HJT) made of thin silicon layers on monocrystalline silicon substrate is an excellent candidate to reach photovoltaic solar cells with light conversion efficiencies above 20 %, even at the industrial production level[1]. High efficiency, low temperature processing, simple device structure, compatibility with thin wafers (< 100 µm) or small temperature coefficient are some of the advantages of Si-HJT that enable a considerable reduction of the manufacturing costs per Watt peak. As shown in Figure 1, Si-HJT, cells built on n-type substrates, are constituted on the font (illumination) side successively by an intrinsic amorphous silicon passivation layer and a pdoped amorphous silicon emitter both deposited by plasma enhanced chemical vapor deposition (PECVD). On top of the silicon layers, an antireflective transparent conductive oxide (TCO) is deposited by physical vapor deposition (PVD) and the charge collection is made by a screen printed metallic contacting grid. On the back side, the stack is realized of an intrinsic amorphous silicon passivation layer, a back-surface field (BSF) layer made of n-type amorphous silicon both deposited by PECVD, a TCO layer and a metallic contacting layer. For a successful mass production of Si-HJT cells, PECVD and PVD large area deposition reactors have to fulfill several criteria. The two most important are: • A very high uniformity to reduce the intra-run spread in passivation quality in order to achieve narrow distribution in final cell performances. • A very well controlled discharge ignition to guarantee inter-run reproducibility and a thickness control at the sub-nanometer level, since the layers are extremely thin (10 nm range). In contrast to reactors used for the production of thin film so
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