High energy yield Bifacial-IBC solar cells enabled by poly-SiOx carrier selective passivating contacts

Abstract

Carrier selective passivating contacts (CSPC) are promising contact structures for high efficiency silicon solar cells. They provide silicon surface passivation as well as high carrier selectivity. In this thesis, the bifacial interdigitate back contacted cell concept (bifacial IBC) is combined with the interdigitated back-contacted (IBC) structure with the bifacial concept for the purpose of further improve the solar cell output. It is enabled by poly-SiOX as CSPCs. The main aim of this thesis project is the preparation of proof of concept bifacial IBC cells. In this work, two process flowcharts for bifacial IBC solar cell fabrication are presented: (1) poly-SiOX fingers patterned by ion-implantation through photoresist masking layer, (2) wet chemical patterning of in-situ doped poly-SiOX. In the first process, the optimization of poly-SiOx passivating contact was performed by varying the intrinsic a-SiOx:H layer thickness. The best passivation results obtained from this approach was 646 mV, and 623 mV for the n+ and p+ layer, respectively. In the second process, the thickness of doped p+ and n+ poly-SiOx layers was also optimized for the symmetrical test samples based on the requirement of bifacial IBC solar cell flowchart. As a consequence, a 25 nm thick p+ poly-SiOx layer and a 40 nm thick n+ poly-SiOx layer recorded highest iVOC performance. Next, the hydrogenation treatment is applied to further optimize the samples passivation quality. This results in an overall passivation of 714 and 730 mV for p+ and n+ poly-SiOX symmetrical samples, owed to the fact that the high hydrogen content in SiNX layer boosting the passivation properties of the poly-SiOX passivating contacts.These findings of the optimized poly-SiOX passivation contacts are used to fabricate the bifacial-IBC solar cell. As a result, using the wet-etching patterning of in-situ poly-SiOX CSPC flow chart, a demonstration proof of this cell principle is obtained with VOC of 649 mV, FF of 44,3 %, JSC of 40,7 mA/cm2, and efficiency of 12% for the best solar cell. The losses analysis of such cell performance was also conducted.