Only recently, methods for quality control of multicrystalline silicon wafers have been published, which allow the efficiency of solar cells to be predicted precisely from photoluminescence (PL) images taken in the as-cut state. In this letter it is shown that oxygen precipitates, present in standard Czochralski silicon wafers, can cause efficiency losses of more than 4% (absolute) within an industrial solar cell proc- ess. These efficiency losses correlate with ring-like defect structures of reduced intensity in the PL image. In comparison with QSSPC-based lifetime measurements, we introduce a PL-based method of quality control which allows the critical wafers to be identified and sorted out reliably at an early state of production and thus increases yield and average efficiency of production lines

Defects in multicrystalline silicon for photovoltaic applications and their impact on solar cell parameters have been investigated in the material research network project SolarFocus. A series of multicrystalline silicon ingots of ultrapure feedstock material were cast with intentional addition of typical transition metal impurities (Fe, Cu, Cr) and Ge as doping elements. The results of lifetime measurements, NAA and FTIR analysis, solar cell processing and microscopic investigations are presented in this study. For ingots intentionally contaminated with transition metals, the combined analysis reveals that despite the overall high impurity content, good solar cell efficiencies can be reached. A strong influence of the in-diffusion of metal impurities from the crucible as well as the back-diffusion from the top region of the ingot ca still be observed. All metals show a strong precipitation behaviour throughout the whole ingot. The solar cell efficiency is both limited by multiple recombination active defects and shunts, induced by a high metal contamination via indirect mechanisms. Solar cells with efficiencies up to 15.2% for material contaminated with 20 ppma Fe in the melt, 15.7% for 20 ppma Cu and 15.1% for 20 ppma Cr were processed. A positive effect of Cu added to the feedstock could not be found. Ge-rich ingots showed strong effects of increasing silicon carbide and silicon nitride formation with increasing Ge content larger than 0.5 wt.% thus reducing solar cell efficiency

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Rapid thermal processing can offer many advantages, such as small overall thermal budget and low power and time consumption, in a strategy focused on cost‐effective techniques for the preparation of solar cells in a continuous way. We show here that this very short duration (a few tens of seconds) of isothermal heating performed in a lamp furnace can be used for many thermal steps of silicon solar cell processing. Rapid thermal processing was applied to form the p‐n junction from a phosphorus‐doped spin‐on silica film deposted on (100) silicon substrates at typical processing temperatures between 800 and 1100°C. the solar cells showed conversion efficiencies as good as those processed in a conventional way.