Dicyanovinylene-Substituted Selenophene-Thiophene Co-oligomers for Small-Molecule Organic Solar Cells

We report on the design, synthesis, and characterization of a series of terminal dicyanovinylene-substituted quinquechalcogenophenes as light-harvesting small-molecule donor materials for organic solar cells. The spectroscopic, electrochemical, and thermal properties of these pentamers were investigated. The replacement of thiophene unit(s) by selenophene(s) results in a bathochromic shift of the longest wavelength absorption band with concomitant increase of the molar extinction coefficient. Cyclic voltammetry measurements revealed fully reversible oxidation and irreversible reduction processes. The highest occupied and lowest unoccupied molecular orbital (HOMO/LUMO) energy levels were determined from electrochemical measurements and lie in the range of -5.6 and -3.8 eV. Vacuum-deposited bulk-heterojunction solar cells fabricated with the novel chalcogenophenes as donor and C-60 as acceptor displayed high open-circuit voltages of up to 1 V, short-circuit currents close to 8 mA.cm(-2), and power conversion efficiencies over 3%.