DOE PAGES title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Understanding Interfacial Alignment in Solution Coated Conjugated Polymer Thin Films

Journal Article · · ACS Applied Materials and Interfaces

Domain alignment in conjugated polymer thin films can significantly enhance charge carrier mobility. However, the alignment mechanism during meniscus-guided solution coating remains unclear. Furthermore, interfacial alignment has been rarely studied despite its direct relevance and critical importance to charge transport. In this study, we uncover a significantly higher degree of alignment at the top interface of solution coated thin films, using a donor–acceptor conjugated polymer, poly(diketopyrrolopyrrole-co-thiopheneco- thieno[3,2-b]thiophene-co-thiophene) (DPP2T-TT), as the model system. At the molecular level, we observe in-plane π–π stacking anisotropy of up to 4.8 near the top interface with the polymer backbone aligned parallel to the coating direction. The bulk of the film is only weakly aligned with the backbone oriented transverse to coating. At the mesoscale, we observe a well-defined fibril-like morphology at the top interface with the fibril long axis pointing toward the coating direction. Significantly smaller fibrils with poor orientational order are found on the bottom interface, weakly aligned orthogonal to the fibrils on the top interface. The high degree of alignment at the top interface leads to a charge transport anisotropy of up to 5.4 compared to an anisotropy close to 1 on the bottom interface. We attribute the formation of distinct interfacial morphology to the skin-layer formation associated with high Peclet number, which promotes crystallization on the top interface while suppressing it in the bulk. As a result, we further infer that the interfacial fibril alignment is driven by the extensional flow on the top interface arisen from increasing solvent evaporation rate closer to the meniscus front.

Research Organization:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Grant/Contract Number:
AC02-06CH11357
OSTI ID:
1376901
Journal Information:
ACS Applied Materials and Interfaces, Journal Name: ACS Applied Materials and Interfaces Journal Issue: 33 Vol. 9; ISSN 1944-8244
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English

References (60)

An Improved Optical Method for Determining the Order Parameter in Thin Oriented Molecular Films and Demonstration of a Highly Axial Dipole Moment for the Lowest Energy π–π* Optical Transition in Poly(9,9- dioctylfluorene-co-bithiophene) journal February 2007
Temperature-Resolved Local and Macroscopic Charge Carrier Transport in Thin P3HT Layers journal June 2010
Anisotropy of Charge Transport in a Uniaxially Aligned and Chain-Extended, High-Mobility, Conjugated Polymer Semiconductor journal January 2011
Anisotropic Structure and Charge Transport in Highly Strain-Aligned Regioregular Poly(3-hexylthiophene) journal August 2011
The Importance of Bridging Points for Charge Transport in Webs of Conjugated Polymer Nanofibers journal January 2012
Effects of Confinement on Microstructure and Charge Transport in High Performance Semicrystalline Polymer Semiconductors journal November 2012
Morphological Origin of Charge Transport Anisotropy in Aligned Polythiophene Thin Films journal February 2014
High‐Performance Organic Thin‐Film Transistors through Solution‐Sheared Deposition of Small‐Molecule Organic Semiconductors journal July 2008
Charge-Transport Anisotropy Due to Grain Boundaries in Directionally Crystallized Thin Films of Regioregular Poly(3-hexylthiophene) journal April 2009
Molecular Characterization of Organic Electronic Films journal August 2010
High-Performance Ambipolar Diketopyrrolopyrrole-Thieno[3,2- b ]thiophene Copolymer Field-Effect Transistors with Balanced Hole and Electron Mobilities journal October 2011
High-Mobility Field-Effect Transistors Fabricated with Macroscopic Aligned Semiconducting Polymers journal February 2014
Highly Oriented Polymer Semiconductor Films Compressed at the Surface of Ionic Liquids for High-Performance Polymeric Organic Field-Effect Transistors journal August 2014
Charge-Transport Anisotropy in a Uniaxially Aligned Diketopyrrolopyrrole-Based Copolymer journal October 2015
On the Extraction of Charge Carrier Mobility in High-Mobility Organic Transistors journal November 2015
Enhanced Polymer Thin Film Transistor Performance by Carefully Controlling the Solution Self-Assembly and Film Alignment with Slot Die Coating journal June 2015
Low-flow limit in slot coating of dilute solutions of high molecular weight polymer journal April 2004
Shear Induced Alignment of Low Aspect Ratio Gold Nanorods in Newtonian Fluids journal September 2015
Modeling Flow Coating of Colloidal Dispersions in the Evaporative Regime: Prediction of Deposit Thickness journal December 2016
NEXAFS Spectroscopy Reveals the Molecular Orientation in Blade-Coated Pyridal[2,1,3]thiadiazole-Containing Conjugated Polymer Thin Films journal September 2015
Direct Uniaxial Alignment of a Donor–Acceptor Semiconducting Polymer Using Single-Step Solution Shearing journal March 2016
Microfluidic Crystal Engineering of π-Conjugated Polymers journal July 2015
Reversible Soft-Contact Lamination and Delamination for Non-Invasive Fabrication and Characterization of Bulk-Heterojunction and Bilayer Organic Solar Cells journal August 2010
Charge Transport in Organic Semiconductors journal April 2007
Quantitative Determination of Organic Semiconductor Microstructure from the Molecular to Device Scale journal June 2012
Lamination Method for the Study of Interfaces in Polymeric Thin Film Transistors journal November 2004
Observation of a Distinct Surface Molecular Orientation in Films of a High Mobility Conjugated Polymer journal January 2013
Alignment of Dispersions of Plate-Like Colloidal Particles of Ni(OH) 2 Induced by Elongational Flow journal April 2011
Drying of a Solution in a Meniscus: A Model Coupling the Liquid and the Gas Phases journal September 2010
Large Scale Alignment and Charge Transport Anisotropy of pBTTT Films Oriented by High Temperature Rubbing journal May 2013
High Mobility Field Effect Transistors Based on Macroscopically Oriented Regioregular Copolymers journal February 2012
Microstructure of Polycrystalline PBTTT Films: Domain Mapping and Structure Formation journal January 2012
Controlling the Orientation of Terraced Nanoscale “Ribbons” of a Poly(thiophene) Semiconductor journal March 2009
Charge separation in localized and delocalized electronic states in polymeric semiconductors journal April 1998
Capillary flow as the cause of ring stains from dried liquid drops journal October 1997
Tuning charge transport in solution-sheared organic semiconductors using lattice strain journal December 2011
Approaching disorder-free transport in high-mobility conjugated polymers journal November 2014
Mobility overestimation due to gated contacts in organic field-effect transistors journal March 2016
Molecular origin of high field-effect mobility in an indacenodithiophene–benzothiadiazole copolymer journal July 2013
Macroscopic and high-throughput printing of aligned nanostructured polymer semiconductors for MHz large-area electronics journal September 2015
Highly oriented crystals at the buried interface in polythiophene thin-film transistors journal February 2006
Large modulation of carrier transport by grain-boundary molecular packing and microstructure in organic thin films journal November 2009
A molecular design principle of lyotropic liquid-crystalline conjugated polymers with directed alignment capability for plastic electronics journal March 2013
A general relationship between disorder, aggregation and charge transport in conjugated polymers journal August 2013
Exploring the origin of high optical absorption in conjugated polymers journal May 2016
A nanogroove-guided slot-die coating technique for highly ordered polymer films and high-mobility transistors journal January 2016
Control of mesoscale and nanoscale ordering of organic semiconductors at the gate dielectric/semiconductor interface for organic transistors journal January 2010
Rotation and alignment of rods in two-dimensional chaotic flow journal April 2011
Solution-processed, high-performance n-channel organic microwire transistors journal March 2009
Anisotropic particles align perpendicular to the flow direction in narrow microchannels journal April 2013
Chain conformations dictate multiscale charge transport phenomena in disordered semiconducting polymers journal September 2013
Optical constants of highly stretch-oriented poly( p -phenylene-vinylene): A joint experimental and theoretical study journal October 2000
Transverse Alignment of Fibers in a Periodically Sheared Suspension: An Absorbing Phase Transition with a Slowly Varying Control Parameter journal December 2011
Reduction and analysis of SANS and USANS data using IGOR Pro journal November 2006
The 30 m Small-Angle Neutron Scattering Instruments at the National Institute of Standards and Technology journal June 1998
The dedicated high-resolution grazing-incidence X-ray scattering beamline 8-ID-E at the Advanced Photon Source journal June 2012
GIXSGUI : a MATLAB toolbox for grazing-incidence X-ray scattering data visualization and reduction, and indexing of buried three-dimensional periodic nanostructured films journal April 2015
Evaluating Rigid and Semiflexible Fiber Orientation Evolution Models in Simple Flows journal October 2016
Numerical simulation of complex fluid drying in a Hele-Shaw cell journal March 2013
Engineering semiconducting polymers for efficient charge transport journal June 2015

Cited By (4)

Enhancing Molecular Alignment and Charge Transport of Solution-Sheared Semiconducting Polymer Films by the Electrical-Blade Effect journal May 2018
Quantitative Image Analysis of Fractal‐Like Thin Films of Organic Semiconductors journal August 2019
Increased charge carrier mobility and molecular packing of a solution sheared diketopyrrolopyrrole-based donor–acceptor copolymer by alkyl side chain modification journal January 2019
Design rules for dynamic-template-directed crystallization of conjugated polymers journal January 2020