This report shares project results and lessons learnt midway through the ‘Earth-abundant, RoHS-compliant antimony chalcogenide: top cell alternative for silicon tandem cells’ project.
The project aims to improve the cost effectiveness of current mass-market Silicon (Si) solar panels by developing high efficiency Si-based tandem cells with our proposed antimony chalcogenide (Sb2(S,Se)3) thin film photovoltaic (PV) material. To achieve lower levelized cost of energy (LCOE) of Si tandem cell than Si cells, while with improved efficiency, the requirement for low degradation rate of Si tandems is also critical. According to International Technology Roadmap for Photovoltaic (ITRPV), a Si-based tandem cell needs to follow the criteria of <2% degradation after the first year of operation and 0.5% per year afterwards. Despite the reported progress on the high bandgap top cells, there is no affirmable top cell solution yet to meet the above requirements of stability, cost-effectiveness and high-efficiency due to either the poor stability, toxicity (perovskite solar cells), and/or scarce constituent (high bandgap Copper Indium Gallium Sulfide, CIGS, solar cells), and/or relatively low performance (high bandgap kesterite solar cells), compromising the possible availability of a fully sustainable thin film PV technology for Si-based tandem cells in a reasonable time-frame. Our project focusses on an alternative top cell which is ultra thin, uses abundant and Restriction of Hazardous Substances (RoHS)-compliant materials and has long-term stable performance. Besides, it can be manufactured using a highly compatible and cost-effective process thus providing an appealing option for Si-based tandem solar cells.