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 '-((2Z,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-1H-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 mA cm(-2) and a higher fill factor of 72.78% 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.