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The unique properties of boron dipyrromethene (BODIPY) dyes including facile synthesis, high absorption coefficients, and delocalized molecular orbitals as well as excellent photochemical and thermal stability, make them promising as materials for organic solar cells. Accordingly, in this study three A- D-A structural small molecules of BDTT-BODIPY, FL-BODIPY, and TT-BODIPY have been synthesized, in which two BODIPY acceptor units are symmetrically conjugated to 4,8-bis(5-(2-ethylhexyl) thiophen-2-yl)benzo[1,2-b:4,5-b]dithiophene (BDTT), 9,9-dioctyl-9H-fluorene (FL), and thieno[3,2-b]thiophene (TT) donor cores, respectively. The manipulation of the structural parameters significantly improves the performances of the BHJ OSCs, which show power conversion efficiencies of 4.75 %, 1.51 %, and 1.67 % based on [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) as the acceptor material and BDTT-BODIPY, FL-BODIPY, and TT-BODIPY as the donor materials, respectively. [ABSTRACT FROM AUTHOR]

Highlights: [•] 4,4′-Bipyridyl was used to increase the ordering of the porphyrin π-system. [•] The ordered structure was confirmed by morphology studies, absorption spectra and XRD. [•] A significantly enhanced charge mobility and solar cell performance were obtained. [•] The results demonstrated a new efficient strategy to develop high efficiency OSCs. [Copyright &y& Elsevier]

Abstract: Alternating low bandgap π-conjugated polymers consisting of 5,7-dithien-2-yl-thieno[3-4-b]pyrazine and phenylene linked directly (PP-DTTP) and by ethynylene linkages (PPE-DTTP) have been prepared in high yields by Suzuki coupling polymerization and Sonogashira condensation, respectively. Thin films of PPE-DTTP and PP-DTTP exhibit an optical bandgap of 1.55 and 1.36eV, respectively, and the devices provide estimated power conversion efficiencies (PCE) of 0.82% and 0.30%, respectively, in bulk heterojunction solar cells with [6,6]-phenyl C61 butyric acid methyl ester (PCBM) as the acceptor. Preliminary optimizations of the devices based on PPE-DTTP gave 1.20% PCE, which ranks in one of the best PCEs of thieno[3-4-b]pyrazines based solar cells. After the introduction of ethynylene linkages in PPE-DTTP, a higher open circuit voltage and a higher short circuit current were obtained with no loss of the fill factor though PPE-DTTP has a higher bandgap, therefore PPE-DTTP shows better performance, which was contributed by the more efficient intramolecular electron transport in PPE-DTTP demonstrated by the hole mobility results and quantum chemistry calculations. [Copyright &y& Elsevier]

The cover page of the journal "Chinese Journal of Chemistry" is presented.