Cyclopentadithiophene-based co-oligomers for solution-processed organic solar cells

A new family of low band-gap co-oligomers based on 4H-cyclopenta[2,1-b:3,4-b']dithiophene (CPDT) and thieno[3,2-b]thiophene (TT) units as central electron-donor cores has been synthesized and characterized for use as electron-donor materials in solution-processed bulk-heterojunction organic solar cells. An in-depth study into the role played by the hexyl chains linked to the thienylenevinylene-based π-bridge has been carried out. Power conversion efficiencies (PCE) of up to 4% and external quantum efficiencies as high as 50% have been achieved. Experiments carried out after solvent vapour annealing (SVA) as a post-treatment led to a doubling of the fill factor (FF) and PCE.