Highly doped polysilicon (poly-Si) on ultra-thin oxide layers are highlighted as they allow both carrier collection efficiency with a low contact resistivity and an excellent surface passivation. Their integration at the rear surface of a highquality single-crystalline silicon solar cell allows to achieve a record conversion efficiency of 25.7% for a double-side contacted device. However, so far, only a very few studies investigate the interactions between poly-Si passivating contacts and low-quality cheaper silicon wafers. Thus, this study focuses on the external gettering response of both boron (B) and phosphorus (P) in situ doped poly-Si passivating contacts on high-performance multicrystalline silicon. Wafers are extracted from five ingot heights and experience P-and B-doped poly-Si passivating contact fabrication processes. Subsequently, the bulk carrier lifetime and interstitial iron (Fe i ) concentration are characterized and compared with conventional POCl 3 and BCl 3 thermal diffusion steps, and as-cut references. The P-doped poly-Si contact fabrication process results in gettering more than 99% of the Fe i , which leads to an increase in the bulk carrier lifetime. Interestingly, the B-doped poly-Si contact also develops a substantial external gettering action, and allows removing 96% of the Fe i from the bulk.

We studied the influence of copper (Cu) on the performances of conventional photovoltaic (PV) solar cells by growing two multicrystalline (mc) boron‐doped silicon (Si) ingots from ultra‐pure feedstocks, one of these feedstocks being deliberately contaminated with 90 ppm wt of Cu. Industrial‐like solar cells were fabricated and the associated external gettering and hydrogenation effects were studied. An originality of our approach consisted in evaluating the forward but also reverse current‐voltage (I‐V) characteristics of the fabricated cells. Furthermore we assessed the stability under illumination of the PV parameters as Cu is known to be responsible for light‐induced degradations (LID) of the carrier lifetime. On the one hand we unexpectedly showed that the PV conversion efficiency (η) was not affected by the initially large Cu concentrations. We demonstrated that it was due to the complementary actions of the external gettering effect developed by the phosphorus‐diffusion and the bulk hydrogenation. The Cu‐addition slightly enhanced the pn junction hard breakdown, however the extracted junction breakdown voltages fulfilled the common industrial requirements for this parameter. On the other hand we highlighted significant decreases under illumination of the PV performances for the Cu‐contaminated solar cells fabricated from wafers coming from the upper part of the ingot (i.e., samples with the highest Cu concentration). These decreases could be explained by the previously proposed mechanisms in the literature, which argue that the excess charge carriers could reduce the electrostatic repulsion between interstitial Cu ions and Cu precipitates, this effect enhancing the Cu precipitation. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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