A series of selenium-containing non-fullerene acceptors with side chain engineering for organic solar cells

Abstract

Non-fullerene acceptors (NFAs) have been crucial in improving the efficiency of organic solar cells (OSCs) due to their attractive properties, such as strong light-harvesting ability, easily tunable energy levels, and high crys-tallinity. Nevertheless, general NFAs have limited light absorption, and studies on the design of NFAs that can absorb a broad range of the solar spectrum and that offer complementary absorption to that of donors should be conducted. Because selenium, a chalcogen element, can induce strong intermolecular SeMIDLINE HORIZONTAL ELLIPSISSe interactions, planarity, and extended effective conjugated length in OSC materials, NFAs with selenium usually exhibit redshifted absorption. Here, we synthesized a series of selenium-containing non-fullerene acceptors with different inner alkyl chain lengths, named Se-Y6-BO (2,2'-((2Z, 2 ' Z)-((12,13-bis(2-butyloctyl)-3,9-dinonyl-12,13-dihydroselenopheno[2 '',3":4 ',5']thieno[2 ',3':4,5]pyrrolo[3,2-g]selenopheno[2 ',3':4,5]thieno [3,23,2-b] [1,2,5] thiadiazolo [3,43,4-e]indole-2,10-diyl)bis(methanylylidene))bis(5,6-dichloro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile) and Se-Y6-HD (2,2'-((2Z, 2 ' Z)-((12,13-bis(2-hexyldecyl)-3,9-dinonyl-12,13-dihy-droselenopheno[2 '',3":4 ',5']thieno[2 ',3':4,5]pyrrolo[3,2-g]selenopheno[2 ',3':4,5]thieno [3,23,2-b] [1,2,5]thia-diazolo [3,43,4-e]indole-2,10-diyl)bis(methanylylidene))bis(5,6-dichloro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile). The optical absorption of two selenium-containing NFAs was redshifted compared with that of Y6 due to the effect of selenium atoms in the backbone. The PM6:Se-Y6-BO-based devices achieved a power conversion efficiency (PCE) of 13.8% with an open-circuit voltage (VOC) of 0.81 V, short-circuit current density (JSC) of 24.4 mA cm-2, and a fill factor of 0.70. Similarly, the OSCs based on PM6:Se-Y6-HD achieved a PCE of 13.6% and a JSC of 23.7 mA cm-2.