Hotspots, frontiers, and emerging trends of tandem solar cell research: A comprehensive review

A tandem solar cell (TSC) is a kind of special photovoltaic (PV) device with two or further sub-cells stacked in it. On the basis of Web of Science database and CiteSpace software, the literature about TSC research from 2000 to 2019 is reviewed. The top 10 hotspots are deduced (efficiency, performance, film, silicon, design, open circuit voltage, polymer, morphology, oxide, and growth), yielding prominence of the primary roles of devices and materials in PV research. The top 10 research clusters are analyzed (organic compounds, polymer solar cells, perovskite, non-fullerene acceptors, silicon, high frequency-glow discharge, solution process, light trapping, liquid phase epitaxy, and water splitting), revealing the development orientation of TSC research. High co-citation, strong burst citation, and representative frontier literature are highlighted. Five evolution trends/clusters are examined. Organic solar cells are the mainstream of TSC research and are gradually replaced by the emerging trend of non-fullerenes. Perovskite solar cells are a typical emerging trend, which rejuvenates the traditional silicon solar cells. This review provides a visual panorama of TSC research over the past two decades.