Journal
CHEMPHYSCHEM
Volume 20, Issue 20, Pages 2608-2626Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cphc.201900793
Keywords
crystal structure; density functional calculations; molecular modelling; non-fullerene; solar cells
Funding
- Basic Energy Sciences [DE-SC0001059] Funding Source: Medline
- U.S. Department of Energy, Office of Science Funding Source: Medline
- Energy Frontier Research Center Funding Source: Medline
- Center for Light Energy Activated Redox Processes (LEAP) Funding Source: Medline
- U.S. Department of Energy (DOE) [DE-SC0001059] Funding Source: U.S. Department of Energy (DOE)
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Accurate single-crystal X-ray diffraction data offer a unique opportunity to compare and contrast the atomistic details of bulk heterojunction photovoltaic small-molecule acceptor structure and packing, as well as provide an essential starting point for computational electronic structure and charge transport analysis. Herein, we report diffraction-derived crystal structures and computational analyses on the n-type semiconductors which enable some of the highest efficiency organic solar cells produced to date, 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2 ',3 '-d ']-s-indaceno[1,2-b:5,6-b ']dithiophene (ITIC) and seven derivatives (including three new crystal structures: 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-propylphenyl)-dithieno[2,3-d:2 ',3 '-d ']-s-indaceno[1,2-b:5,6-b ']dithiophene (ITIC-C3), 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(3-hexylphenyl)-dithieno[2,3-d:2 ',3 '-d ']-s-indaceno[1,2-b:5,6-b ']dithiophene (m-ITIC-C6), and 3,9-bis(2-methylene-((3-(1,1-dicyanomethylene)-6,7-difluoro)-indanone))-5,5,11,11-tetrakis(4-butylphenyl)-dithieno[2,3-d:2 ',3 '-d ']-s-indaceno[1,2-b:5,6-b ']dithiophene (ITIC-C4-4F). IDTT acceptors typically pack in a face-to-face fashion with pi-pi distances ranging from 3.28-3.95 angstrom. Additionally, edge-to-face packing is observed with SMIDLINE HORIZONTAL ELLIPSIS pi interactions as short as 3.21-3.24 angstrom. Moreover, ITIC end group identities and side chain substituents influence the nature and strength of noncovalent interactions (e. g. H-bonding, pi-pi) and thus correlate with the observed packing motif, electronic structure, and charge transport properties of the crystals. Density functional theory (DFT) calculations reveal relatively large nearest-neighbor intermolecular pi-pi electronic couplings (5.85-56.8 meV) and correlate the nature of the band structure with the dispersion interactions in the single crystals and core-end group polarization effects. Overall, this combined experimental and theoretical work reveals key insights into crystal engineering strategies for indacenodithienothiophene (IDTT) acceptors, as well as general design rules for high-efficiency post-fullerene small molecule acceptors.
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