Donor and Acceptor Unit Sequences Influence Material Performance in Benzo[1,2-b:4,5-b′]dithiophene-6,7-Difluoroquinoxaline Small Molecule Donors for BHJ Solar Cells
Wolf, Jannic Sebastian
Hansen, Michael Ryan
KAUST DepartmentKAUST Solar Center (KSC)
Physical Sciences and Engineering (PSE) Division
Materials Science and Engineering Program
KAUST Grant NumberCRG_R2_13_BEAU_KAUST_1
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AbstractWell-defined small molecule (SM) donors can be used as alternatives to π-conjugated polymers in bulk-heterojunction (BHJ) solar cells with fullerene acceptors (e.g., PC61/71BM). Taking advantage of their synthetic tunability, combinations of various donor and acceptor motifs can lead to a wide range of optical, electronic, and self-assembling properties that, in turn, may impact material performance in BHJ solar cells. In this report, it is shown that changing the sequence of donor and acceptor units along the π-extended backbone of benzo[1,2-b:4,5-b']dithiophene-6,7-difluoroquinoxaline SM donors critically impacts (i) molecular packing, (ii) propensity to order and preferential aggregate orientations in thin-films, and (iii) charge transport in BHJ solar cells. In these systems (SM1-3), it is found that 6,7-difluoroquinoxaline ([2F]Q) motifs directly appended to the central benzo[1,2-b:4,5-b']dithiophene (BDT) unit yield a lower-bandgap analogue (SM1) with favorable molecular packing and aggregation patterns in thin films, and optimized BHJ solar cell efficiencies of ≈6.6%. 1H-1H DQ-SQ NMR analyses indicate that SM1 and its counterpart with [2F]Q motifs substituted as end-group SM3 possess distinct self-assembly patterns, correlating with the significant charge transport and BHJ device efficiency differences observed for the two analogous SM donors (avg. 6.3% vs 2.0%, respectively). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
CitationWang K, Liang R-Z, Wolf J, Saleem Q, Babics M, et al. (2016) Donor and Acceptor Unit Sequences Influence Material Performance in Benzo[1,2-b:4,5-b′]dithiophene-6,7-Difluoroquinoxaline Small Molecule Donors for BHJ Solar Cells. Advanced Functional Materials 26: 7103–7114. Available: http://dx.doi.org/10.1002/adfm.201602162.
SponsorsK.W. and R.-Z.L. contributed equally to this work. This publication is based upon work supported by the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under Award No. CRG_R2_13_BEAU_KAUST_1. The authors acknowledge concurrent support under Baseline Research Funding from KAUST. The authors thank KAUST ACL for technical support in the mass spectrometry analyses. M.R.H. acknowledges the Villum Foundation, Denmark under the Young Investigator Programme (VKR023122). P.M.B. and P.W. thank Dr. Mahesh K. Ravva for useful technical discussions and input in our DFT studies.
JournalAdvanced Functional Materials