Photovoltaic performance of an ultrasmall band gap polymer

A conjugated polymer (PBTTQ) that consists of alternating electron-rich bithiophene and electron-deficient thiadiazoloquinoxaline units was synthesized via Yamamoto polymerization with Ni(cod)(2) and provides a band gap of 0.94 eV. This represents one of the smallest band gaps obtained for a soluble conjugated polymer. When applied in a bulk heterojunction solar cell together with [84]PCBM as the electron acceptor, the polymer affords a response up to 1.3 mu m

Fine-Tuning of Molecular Energy Level of Alternating Copolymers On the basis of [1,2,5]Thiadiazolo[3,4- g

A series of low-bandgap alternating copolymers consisting of electron-accepting [1,2,5]thiadiazolo[3,4-g]quinoxaline (TQ) derivatives and electron-donating fluorene or carbazole were synthesized via the Suzuki coupling reaction. For the purpose to fine-tune the molecular energy level of alternating copolymers and thus to improve charge transfer between polymers and PCBM, two different TQ derivatives substituted with strongly electron-donating butoxy group or weakly electron-donating thienyl group were synthesized and used as a building block of alternating copolymers. Copolymers with butoxy-substituted TQ have proper lowest unoccupied molecular orbital (LUMO) energy levels for effective charge dissociation between polymer and PCBM, whereas the LUMO levels of copolymers with thienyl-substituted TQ are too close to that of PCBM to be effective for charge dissociation. The power conversion efficiency was achieved up to 2.17%, which is the highest value among the TQ:based polymer solar cells, when the blend of copolymer with butoxy-substituted TQ and [6,6]phenyl-C-71-butyric acid methyl ester was used as an active layer material in bulk heterojunction solar cells.N