A chlorinated low-bandgap small-molecule acceptor for organic solar cells with 14.1% efficiency and low energy loss
A new acceptor-donor-acceptor (A-D-A) type small-molecule acceptor NCBDT-4Cl using chlorinated end groups is reported. This new-designed molecule demonstrates wide and efficient absorption ability in the range of 600–900 nm with a narrow optical bandgap of 1.40 eV. The device based on PBDB-T-SF:NCBDT-4Cl shows a power conversion efficiency (PCE) of 13.1% without any post-treatment, which represents the best result for all as-cast organic solar cells (OSCs) to date. After device optimizations, the PCE was further enhanced to over 14% with a high short-circuit current density (Jsc) of 22.35 mA cm−2 and a fill-factor (FF) of 74.3%. The improved performance was attributed to the more efficient photo-electron conversion process in the optimal device. To our knowledge, this outstanding efficiency of 14.1% with an energy loss as low as 0.55 eV is among the best results for all single-junction OSCs.
Keywordssmall-molecule acceptor low-bandgap chlorinated high performance
This work was supported by the National Natural Science Foundation of China (91633301, 51773095), MoST of China (2014CB643502), Tianjin city (17JCJQJC44500, 17CZDJC31100) and 111 Project (B12015). The authors also thank beamline BL14B1 (Shanghai Synchrotron Radiation Facility) for providing the beam time.
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