Alexander Uhl, University of Washington
Solution-Processed Chalcopyrite-Perovskite Tandem Solar Cells in Bandgap-Matched Two-Terminal Architectures
Written by Xiwen Gong
Tandem solar cells exhibit great promise in improving solar power conversion efficiency by making better use of the solar spectrum. In stark contrast with single junction solar cells, which can only absorb photons above the bandgap, tandem cells combine high bandgap material with a low bandgap one, extending their absorption range further toward the short or long wavelength region.
Cu(In,Ga)(S,Se)2 (CIGS) and perovskite solar cells both show the highest efficiency of 22% in a single junction configuration. If we combine these two cells together in a tandem cell, the highest theoretical power conversion efficiency (PCE) can be raised to 45%, with perovskite (1.6 eV) as top cell and CIGS (1.0 eV) as bottom cell.
Alexander Uhl from the University of Washington introduced their work in chalcopyrite perovskite tandem solar cells in the morning session on Thursday. The researchers started from making high efficiency single junction cells made from solution-processed CIGS or CIS (CuIn(S,Se)2). The PCE of 14.7% and 13.0% were achieved from CIGS and CIS, respectively. However, when illuminated with near-infrared light, the fill factor (FF) of the CIS cells can drop dramatically by almost 50%. The researchers solved this FF issue by increasing the concentration of sulfur: the FF kept constant when illuminated in the near-infrared wavelength region when sulfur ratio was increased from 1% to 6%. By delicate design of the tandem cell structure (MAPbI3 on top of CIS), Uhl reported the record high efficiency of 18.5% among solution-processed two-terminal chalcogenide-perovskite tandem solar cells.