Efficient thin epilayer multicrystalline silicon solar cells

Abstract

Liquid Phase Epitaxy (LPE) is a suitable technique for the growth of thin silicon films for photovoltaics, offering low growth temperatures, high utilisation of silicon, and low cost and complexity. Former modelling results showed that it should be possible to reach efficiencies in excess of 18% although using an opaque as a substrate and no light trapping schemes. However, silicon layers grown by LPE on suitable low cost substrates such as low-grade multicrystalline silicon are often very rough, making the processing of the layers difficult. We have used of a modified LPE technique which incorporates intermittent meltback into the growth process to grow silicon on cast multicrystalline wafers. The use of this technique has resulted in a significantly improved surface morphology, as was confirmed by scanning electron microscopy. This improvement can be explained by considering the transport of solute in the melt during the growth and meltback stages. Solar cells fabricated on these layers have achieved efficiencies up to 15.4%, despite the absence of any light confinement. The results also indicate that further performance boosts up to 17% are possible through further refinement of the cell processing techniques.