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Building Blocks for High‐Efficiency Organic Photovoltaics: Interplay of Molecular, Crystal, and Electronic Properties in Post‐Fullerene ITIC Ensembles
Author(s) -
Swick Steven M.,
Gebraad Tim,
Jones Leighton,
Fu Bo,
Aldrich Thomas J.,
Kohlstedt Kevin L.,
Schatz George C.,
Facchetti Antonio,
Marks Tobin J.
Publication year - 2019
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201900793
Subject(s) - methylene , materials science , crystal (programming language) , crystallography , organic solar cell , fullerene , crystal structure , diffraction , acceptor , molecule , chemistry , polymer , organic chemistry , optics , physics , condensed matter physics , computer science , composite material , programming language
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 π–π distances ranging from 3.28–3.95 Å. Additionally, edge‐to‐face packing is observed with S⋯π interactions as short as 3.21–3.24 Å. Moreover, ITIC end group identities and side chain substituents influence the nature and strength of noncovalent interactions (e. g. H‐bonding, π–π) 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 π‐π 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.