Panchromatic Conjugated Polymers Containing Alternating Donor/Acceptor Units for Photovoltaic Applications

Abstract

We designed and synthesized a series of conjugated polymers containing alternating electron-donating and electron-accepting units based on (4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b‘]dithiophene), 4,7-(2,1,3)-benzothiadiazole, and 5,5‘-[2,2‘]bithiophene. These polymers possess an optical band gap as low as 1.4 eV (i.e., in the case of poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b‘]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)]), and their absorption characteristics can be tuned by adjusting the ratio of the two electron-donating units: (4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b‘]dithiophene) and 5,5‘-[2,2‘]bithiophene. The desirable absorption attributes of these materials qualify them as excellent candidates for light-harvesting materials in organic photovoltaic applications allowing for high short-circuit current. Electrochemical studies indicate sufficiently deep HOMO/LUMO levels that enable a high photovoltaic device open-circuit voltage when fullerene derivatives are used as ...