High-efficiency all-small-molecule organic solar cells based on an organic molecule donor with an asymmetric thieno[2,3-f]benzofuran unit

Two p-type small molecules BDTT-TR and TBFT-TR with benzo[1,2-b′:4,5-b′]dithiophene(BDT)and thieno[2,3-f]benzofuran(TBF)as central core units are synthesized and used as donors in all-small-molecule organic solar cells(all-SMOSCs)with a narrow-bandgap small molecule Y6(2,2′-((2 Z,2′Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2″,3’′:4’,5′]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1 H-indene-2,1-diylidene))dimalononitrile)as the acceptor.In comparison to BDTT-TR with centrosymmetric BDT as the central unit,TBFT-TR with asymmetric TBF as the central unit shows red-shifted absorption,higher charge-carrier mobility and better charge pathway in blend films.The power conversion efficiency(PCE)of the all-SMOSCs based on TBFT-TR:Y6 reaches 14.03%with a higher short-circuit current density of 24.59 m A cm-2 and a higher fill factor of72.78%compared to the BDTT-TR:Y6 system.The PCE of 14.03%is among the top efficiencies of all-SMOSCs reported in the literature to date.