Efficiencies above 16% on Novel Quasi-mono RGS Material

Abstract

To date, solar cells made from kerf-less and cost-effective Ribbon Growth on Substrate (RGS) Si material suffered heavily from shunting problems. In combination with the low material quality, this led to decreased fill factor values and thus to significantly lower efficiency values compared to block-cast multicrystalline (mc) Si. In this study, a novel RGS material seeded on silicon substrate is investigated. Solar cells made from this new ‘quasi-mono’ material using a lab-type process show VOC values >600 mV and average fill factor values >78%, similar to standard mc-Si. This leads to cell efficiencies >16% (certified by ISE CalLab), which is an enormous progress compared to the former efficiency record of 14.4%. The obtained higher fill factor values are most probably due to the absence of current collecting structures, in contrast to standard RGS material, as shown by infrared microscopy investigation. This was also found comparing Internal Quantum Efficiency topograms and Electroluminescence maps. For this new material, minority carrier lifetime is in the range of 18 μs (after P-gettering and hydrogenation) and hence approximately two times higher than for standard RGS, which explains the higher achieved VOC. Furthermore, the bulk quality of this novel RGS material is more homogeneous and its grain orientation is predominantly (100), allowing the use of an alkaline texture.