Improvement of the optoelectronic and photovoltaic properties of a cyanopyrid-2,6-dione-based donor via molecular engineering

Through the molecular engineering of cyanopyrid-2,6-dione functionality, herein we report the design and synthesis of a novel, small molecule electron donor, (Z)-5-((5'-(4-(diphenylamino)phenyl)-[2,2′-bithiophen]-5-yl)methylene)-1-(4-(hexyloxy)phenyl)-4-methyl-2,6-dioxo-1,2,5,6-tetrahydropyridine-3-carbonitrile (coded as CP2), which exhibits improved optoelectronic and photovoltaic properties when compared with its structural analogue (E)-5-((5'-(4-(diphenylamino)phenyl)-[2,2′-bithiophen]-5-yl)methylene)-1-(2-ethylhexyl)-4-methyl-2,6-dioxo-1,2,5,6-tetrahydropyridine-3-carbonitrile (coded as CP1). The molecular engineering helps to achieve more desirable energy levels together with bathochromic shift in the absorption spectrum, which improves the short-circuit current density. A high conversion efficiency of 6.28% was obtained in simple devices (CP2: PC61BM 1: 1) which is one of the best results in the current literature for cyanopyrid-2,6-dione-based small molecule donors.