20.2% EFFICIENCY WITH A-SI:H/C-SI HETEROJUNCTION SOLAR CELLS ON MONO-LIKE SUBSTRATES F.Jay, D.Muñoz, N.Enjalbert, G.D’Alonzo, J.Stendera, S.Dubois, D.Ponthenier, A.Jouini, P.J.Ribeyron CEA-INES, 50 avenue du lac Leman, BP 332, 73377 Le Bourget du Lac cedex France Corresponding author: frederic.jay@cea.fr ABSTRACT: In this work, we present our first results of heterojunction solar cells fabricated on monocrystalline-like n-type substrates. The mono-like ingot was produced using a combination of quartz rod dipping and a modulated conductive heat extraction system, made in-house, in a directional solidification system. First, we evaluated the material quality with symmetrical SiNx layers deposited on different textured samples from different ingots and ingots height. Then, we performed an external gettering treatment to improve the bulk quality of the wafers to attain higher bulk lifetime permitting higher open-circuit voltages typical of heterojunction devices. Finally, we fabricated 148cm² HET solar cells using the so-called industrial compatible process on n-type 170μm wafers. We achieved efficiencies higher than 19% on complete wafers. Optimized 100cm 2 cells without edge damaging showed record efficiencies over 20%. Keywords: monocrystalline-like, mono-like, heterojunction solar cells, high-efficiency 1 INTRODUCTION Nowadays, cost reduction combined with increasing efficiency is mandatory for photovoltaic industry to be competitive. Concerning crystalline silicon technology, it is necessary to use high quality single-crystalline substrates (i.e, Czochralski (Cz) or Float-Zone (FZ)) to reach high efficiency solar cells. Although these growth techniques offer advantages (very low density of extended crystallographic defects), the downside is that the growth process is very expensive and the silicon wafers represent between 30-50% of the total cell fabrication cost [1]. Therefore, major manufacturers in the solar energy industry focus on the wafer cost reduction by improving the silicon ingots productivity or reducing wafer thickness. On the other side high quality wafers can be obtained by developing the seed growth technique for the production of directionally solidified monocrystalline-like silicon wafers, sometimes called mono-like or quasi-mono silicon [2]. The amorphous/crystalline silicon (a-Si:H/c-Si) heterojunction solar cell technology is highly dependent on bulk quality [3]. The key of the technology is the very high surface passivation quality by the a-Si:H layers allowing record open-circuit (V oc ) values (>740mV). Substrates with bulk lifetimes (τ bulk ) over 1ms are mandatory to reach efficiency above 23.7% (demonstrated by Panasonic- Sanyo on 98μm wafers) [4]. In previous work, we demonstrated high efficiency HET solar cells over 21% efficiency on large area [4] improving all technological aspects. Moreover, the simplification of the fabrication process on an industrial compatible one (considering costs and scaling-up) with Cz-Si wafers allowed us to reach 20% efficiency on 125PSQ wafers [5]. The goal of this work is to evaluate the suitability and limitations of mono-like material for the HET technology. Production of mono-like ingots is significantly less expensive than Cz or FZ materials and would strongly impact the production costs. However, it is important to keep the same solar cell’s performance not to increase the total €/W balance. The ultimate goal of the mono-like silicon is to reduce the multicrystalline and defective area (grain boundaries) [2] to reach the same quality as Cz ingots, allowing the same efficiency levels. In this work, the mono-like ingot and all the solar cells fabrication process was developed and characterized at INES. 2 EXPERIMENTAL 2.1 Wafers used All wafers used in this work are n-type mono-like 12.5×12.5cm² wafers with initial thickness of 180μm, and resistivity around 1-2ohm·cm. The single-crystalline zone was <100> oriented. 2.2 Improvement of quality bulk and wafers selection To evaluate the quality of the bulk, we sampled the ingots on different heights and took representative wafers. After a wet chemical etching, we passivated the wafers by a symmetrical deposit of PECVD SiNx:H. Implied-V oc , effective charge carrier lifetime were measured by Sinton WCT-100 and mapped by μW-PCD (semilab WT-2000). On the finished solar cells the minority carrier diffusion length were determined and mapped from LBIC measurements at various near infrared wavelengths (semilab WT-2000). Moreover, we compared the quality of the bulk along the ingot’s height with and without an optimized external gettering treatment (phosphorus diffusion from a POCl 3 source). 2.3 Heterojunction solar cells On selected samples suitable for HET devices, we fabricated complete solar cells. Details on the used process are described elsewhere [5]. The structure of the final HET solar cells is described in figure 1. Cells were characterized by dark, Suns-Voc and IV