Light trapping in polycrystalline silicon thin-film solar cells based on liquid phase crystallization on textured substrates

摘要

Liquid phase crystallization (LPC) is a promising technique to fabricate high-quality polycrystalline silicon absorber layers on cheap glass substrates. Recently, we achieved open-circuit voltages above 580mV using a silicon heterojunction and a newly developed single-sided contact system. However, the still moderate efficiency of 5.7% can be attributed to short circuit current densities not exceeding 16mA/cm2, caused by optical losses and absorber recombination. An approach to tackle the first problem is presented in this work. In general, a proper light management concept for thin film devices involve specially designed anti reflective coatings (ARC) and textured surfaces on both sides of the device, to enhance the optical path of the cell. As the crystals achieved using LPC are up to cm in length, commonly used wet chemical treatments using in wafer-based PV are applicable here, too. However providing a texture to the substrate:silicon interface is more complex as the texture as well as all layers deposited before the crystallization process must withstand the high temperatures present during LPC. However it is possible to deposit adequate inter-layers that enable LPC on randomly textured substrates as shown in this work.