A new wide bandgap small molecular acceptor based on indenofluorene derivatives for fullerene-free organic solar cells

An efficient wide bandgap small molecular electron acceptor 2,2'-((2Z,2′Z)-(((6,6,12,12-tetraoctyl-6,12-dihydroindeno[1,2-b]fluorene-2,8-diyl)bis(thiophene-5,2-diyl))bis(methanylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (IFTIC) based on indenofluorene for organic solar cells was developed. With strong and broad absorption in shortwave region (470-690 nm) and suitable energy levels (HOMO = −5.42 eV, LUMO = −3.85 eV), this newly designed wide bandgap acceptor was able to preferably match the most typical low bandgap polymer donor material poly({4,8-bis[(5-(2-ethylhexyl)-2-thienyl]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7-Th). Benefit from its up-shifted LUMO energy level and complementary absorption spectrum, the inverted device based on IFTIC and PTB7-Th processed power conversion efficiencies (PCE) up to 6.56% and relatively high open circuit voltage (Voc) value (0.92 V). These results demonstrate that the indenofluorene type wide bandgap small molecule could be the promising electron acceptor in organic solar cells.