基于掺杂PECVD硅膜的钝化接触的N型高效硅太阳膜电池-solarbe文库

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Contents lists available at ScienceDirect Solar Energy Materials and Solar Cells journal homepage www.elsevier.com/locate/solmat High eﬃciency n-type silicon solar cells with passivating contacts based on PECVD silicon ﬁlms doped by phosphorus diﬀusion Di Yan 1 , Sieu Pheng Phang 1 , Yimao Wan, Christian Samundsett, Daniel Macdonald ⁎ , Andres Cuevas ⁎ Research School of Engineering, Australian National University, Canberra, ACT 2601, Australia ARTICLE INFO Keywords Carrier-selective passivating contacts PECVD Amorphous silicon High eﬃciency silicon solar cells ABSTRACT Carrier-selective contacts based on silicon ﬁlms deposited onto a thin SiO x layer combine high performance with a degree of compatibility with industrial solar cell metallization steps. This paper demonstrates an approach to form electron-selective passivating contacts that maximises the overlap with common industrial equipment; it is based on depositing an intrinsic amorphous silicon a-Si layer by PECVD and then doping and re-crystallizing it by means of a thermal phosphorus diﬀusion. By optimizing the intrinsic a-Si thickness and the phosphorus diﬀusion temperature, a low recombination current density J oc ≈3 fA/cm 2 and a low contact resistivity of ρ c ≈3mΩ-cm 2 have been achieved. Additionally, these electrical parameters have been found to be sensitive to the work function of the outer metal electrode. The application of these optimized electron-selective passivating contacts to n-type silicon solar cells has permitted to achieve a conversion eﬃciency of 24.7. A loss analysis has been conducted through Quokka 2 simulations, which together with quantum eﬃciency measurements, indicate that further optimization should focus on the front boron-doped region of the device. 1. Introduction Reducing the already low fabrication costs of silicon PV is chal- lenging, but there are promising opportunities and an increasing need, to improve the performance of average production silicon cells and modules. Among them, passivating contacts based on a layer of doped re-crystallized silicon and an ultra-thin layer of silicon oxide formed on top of the silicon wafers can achieve a very high performance [1–5]. Although the deposited silicon layer may be initially amorphous, it is subsequently re-crystallized at a high temperature, becoming largely polycrystalline. This high temperature step makes the polycrystalline silicon/SiO x approach radically distinctive from that used for silicon heterojunction solar cells, which is based on depositing at relatively low temperatures layers of doped and intrinsic amorphous silicon [6,7].An attraction of the high temperature passivating contact approach is that it can have a relatively large overlap and be generically compatible with current industrial solar cell manufacturing equipment and pro- cesses. The approach presented in this paper is to use μW/RF PECVD mi- crowave/radio-frequency plasma enhanced chemical vapour deposition equipment and silane, both of which are commonly used for SiN x antireﬂection coatings, to deposit an intrinsic a-Si layer and then dope it by conventional phosphorus diﬀusion from POCl 3 . Such a doping step simultaneously serves to crystallize the deposited silicon, and slightly in-diﬀuse the dopant into the silicon wafer, both of which are critical to achieve good contact and passivation properties [8,9]. Examples of such diﬀusion optimization of intrinsic Si layers are given in earlier work by Romer et al. [9] and Yan et al. [8–10]. Recently, Liu et al. have demonstrated that adopting this approach to form the pas- sivating contacts is accompanied by strong impurity gettering eﬀects, which provides additional beneﬁts at no extra cost [11,12]. In this paper, we report further optimization of these electron-selective pas- sivating contacts, we study the impact of metals with diﬀerent work functions, and we demonstrate the potential of this approach by fab- ricating n-type silicon solar cells with a 24.7 conversion eﬃciency. 2. Experimental methods The recombination current density J oc and contact resistivity ρ c test samples were prepared separately high resistivity 50Ω-cm 100 https//doi.org/10.1016/j.solmat.2019.01.005 Received 16 July 2018; Received in revised form 21 December 2018; Accepted 3 January 2019 ⁎ Corresponding authors. E-mail addresses di.yananu.edu.au D. Yan, pheng.phanganu.edu.au S.P. Phang, yimoa.wananu.edu.au Y. Wan, chris.samundsettanu.edu.au C. Samundsett, daniel.macdonaldanu.edu.au D. Macdonald, Andres.Cuevasanu.edu.au A. Cuevas. 1 Equal contribution as the ﬁrst authors Solar Energy Materials and Solar Cells 193 2019 80–84 0927-0248/ © 2019 Elsevier B.V. All rights reserved. T n-type FZ Si wafers with symmetrical surface structure of electron-se- lective passivating contacts were used to obtain J oc ; Cox and Strack structures were fabricated on low resistivity 0.5Ω-cm 100 n-type CZ Si wafer to facilitate the extraction of ρ c values [13]. After saw damage etching and standard RCA cleaning, a thin oxide layer was grown on the substrates by immersion in hot nitric acid 68wt solution at a temperature of 90°C for 30min. The ﬁnal oxide thickness was measured to be approximately 1.4nm by ellipso- metry. Subsequently, intrinsic a-Si layers with thicknesses ranging from 50nm to 200nm were deposited using a laboratory-scale μW/RF PECVD system Roth we found that increasing the diﬀusion temperature is eﬀective for thicker as-deposited a-Si layers. By ad- justing the diﬀusion temperature, a very low recombination current density J oc ≈3 fA/cm 2 together with a low contact resistivity ρ c ≈3mΩ-cm 2 have been achieved for a wide range of a-Si thicknesses. By exploring contact formation with diﬀerent metals, we found that low work function metals, such as Ag, are good candidates for such elec- tron-selective passivating contacts fabricated with the approach pre- sented in this paper. By using the optimized layers and processes, n-type silicon solar cells with rear phosphorus doped passivating contacts have been fabricated, achieving a eﬃciency of 24.7. Device simulations and test samples indicate that the performance of these solar cells could be further increased by improving the quality of the front surface passivation. Acknowledgements The authors wish to acknowledge the support of from the Australian Renewable Energy Agency ARENA through the Solar PV research and Development Programme and via Australian Centre for Advanced Photovoltaics ACAP. Equipment at the Canberra node of the Australian National Fabrication Facility was used for some of the ex- perimental work. References [1] F. Feldmann, M. Bivour, C. Reichel, H. Steinkemper, M. Hermle, S.W. Glunz, Tunnel oxide passivated contacts as an alternative to partial rear contacts, Sol. Energy Mater. Sol. Cells 131 0 2014 46–50. [2] U. 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