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Photophysical and morphological implications of single-strand conjugated polymer folding in solution

Journal Article · · Chemistry of Materials
 [1];  [2];  [3];  [3];  [2];  [1]
  1. Northwestern Univ., Evanston, IL (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
  2. The Univ. of Chicago, Chicago, IL (United States)
  3. Northwestern Univ., Evanston, IL (United States)
Organic semiconductors have garnered substantial interest in optoelectronics, but their device performances exhibit strong dependencies on material crystallinity and packing. In an effort to understand the interactions dictating the morphological and photophysical properties of a high-performing photovoltaic polymer, PTB7, a series of short oligomers and low molecular weight polymers of PTB7 were synthesized. Chain-length dependent optical studies of these oligomers demonstrate that PTB7’s low-energy visible absorption is largely due to self-aggregation-induced ordering, rather than in-chain charge transfer, as previously thought. By examining molecular weight and concentration dependent optical properties, supplemented by molecular dynamics simulations, we attribute polymeric PTB7’s unique midgap fluorescence and concentration independent absorption spectrum to an interplay between low molecular weight unaggregated strands and high-molecular weight self-aggregated (folded) strands. Specifically, we propose that the onset of PTB7 self-folding occurs between 7 and 13 repeat units, but the aggregates characteristic of polymeric PTB7 only develop at lengths of ~30 repeat units. Atomistic molecular dynamics simulations of PTB7 corroborate these conclusions, and a simple relation is proposed which quantifies the free-energy of conjugated polymer folding. Lastly, this study provides detailed guidance in the design of intra- and interchain contributions to the photophysical and morphological properties of polymeric semiconductors.
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:
1350686
Journal Information:
Chemistry of Materials, Journal Name: Chemistry of Materials Journal Issue: 8 Vol. 28; ISSN 0897-4756
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English

References (48)

Effective conjugation length and UV/vis spectra of oligomers journal September 1997
Photovoltaic Function and Exciton/Charge Transfer Dynamics in a Highly Efficient Semiconducting Copolymer journal July 2013
Optical Bandgaps of π-Conjugated Organic Materials at the Polymer Limit: Experiment and Theory journal January 2007
When Function Follows Form: Effects of Donor Copolymer Side Chains on Film Morphology and BHJ Solar Cell Performance journal November 2010
A Mechanistic Understanding of Processing Additive-Induced Efficiency Enhancement in Bulk Heterojunction Organic Solar Cells journal October 2013
Understanding Low Bandgap Polymer PTB7 and Optimizing Polymer Solar Cells Based on It journal March 2014
Microcavity-Enhanced Light-Trapping for Highly Efficient Organic Parallel Tandem Solar Cells journal August 2014
Matrix formulation of the transition from a statistical coil to an intramolecular antiparallel β sheet journal September 1984
Fast Parallel Algorithms for Short-Range Molecular Dynamics journal March 1995
Time-resolved fluorescence studies on thiophene oligomers in solution journal September 1993
Synthesis of polystyrene-poly-3 hexylthiophene block copolymers and characterization by x-rays and neutron scattering journal January 1997
Efficiency of bulk-heterojunction organic solar cells journal December 2013
Combined Raman, electrochemical and DFT studies on a series of α, α′-thiophene-phosphole oligomers and their corresponding polymers journal September 2005
Study of Optical Properties and Molecular Aggregation of Conjugated Low Band Gap Copolymers: PTB7 and PTB7-Th journal October 2015
Effect of PTB7 Properties on the Performance of PTB7:PC 71 BM Solar Cells journal June 2015
From Short Conjugated Oligomers to Conjugated Polymers. Lessons from Studies on Long Conjugated Oligomers journal January 2011
Mechanistic Studies of Effect of Dispersity on the Photovoltaic Performance of PTB7 Polymer Solar Cells journal January 2015
Effects of Additives on the Morphology of Solution Phase Aggregates Formed by Active Layer Components of High-Efficiency Organic Solar Cells journal December 2011
Examining the Effect of the Dipole Moment on Charge Separation in Donor–Acceptor Polymers for Organic Photovoltaic Applications journal December 2011
Controlling Conformations of Conjugated Polymers and Small Molecules: The Role of Nonbonding Interactions journal May 2013
Development of New Semiconducting Polymers for High Performance Solar Cells journal January 2009
Conformational Order in Aggregates of Conjugated Polymers journal May 2015
Influence of Regio- and Chemoselectivity on the Properties of Fluoro-Substituted Thienothiophene and Benzodithiophene Copolymers journal June 2015
Microscopic Inhomogeneity and Ultrafast Orientational Motion in an Organic Photovoltaic Bulk Heterojunction Thin Film Studied with 2D IR Vibrational Spectroscopy journal December 2006
Electronic Processes in Conjugated Diblock Oligomers Mimicking Low Band-Gap Polymers: Experimental and Theoretical Spectral Analysis journal November 2010
Revealing Exciton Dynamics in a Small-Molecule Organic Semiconducting Film with Subdomain Transient Absorption Microscopy journal October 2013
Solution Phase Exciton Diffusion Dynamics of a Charge-Transfer Copolymer PTB7 and a Homopolymer P3HT journal December 2014
Exciton Structure and Dynamics in Solution Aggregates of a Low-Bandgap Copolymer journal December 2014
Aggregation Quenching of Luminescence in Electroluminescent Conjugated Polymers journal February 1999
Chromophore-Controlled Self-Assembly of Highly Ordered Polymer Nanostructures journal July 2013
Electroluminescence from Substituted Poly(thiophenes): From Blue to Near-Infrared journal October 1995
Mediating Solar Cell Performance by Controlling the Internal Dipole Change in Organic Photovoltaic Polymers journal July 2012
From Single Chains to Aggregates, How Conjugated Polymers Behave in Dilute Solutions journal July 2013
Polyfluorene Derivatives:  Effective Conjugation Lengths from Well-Defined Oligomers journal March 1998
The Role of N-Doped Multiwall Carbon Nanotubes in Achieving Highly Efficient Polymer Bulk Heterojunction Solar Cells journal May 2013
Molecular Order in High-Efficiency Polymer/Fullerene Bulk Heterojunction Solar Cells journal September 2011
Unmasking Bulk Exciton Traps and Interchain Electronic Interactions with Single Conjugated Polymer Aggregates journal December 2011
Aggregation and morphology control enables multiple cases of high-efficiency polymer solar cells journal November 2014
Resonant energy transfer of triplet excitons from pentacene to PbSe nanocrystals journal October 2014
A quantum-chemical perspective into low optical-gap polymers for highly-efficient organic solar cells journal January 2011
Highly-efficient charge separation and polaron delocalization in polymer–fullerene bulk-heterojunctions: a comparative multi-frequency EPR and DFT study journal January 2013
Characterization of electronic transitions in complex molecules journal January 1950
Resonance energy transfer from organic chromophores to fullerene molecules journal May 2006
A statistical mechanical model for antiparallel β-sheet/coil equilibrium journal December 2008
Interplay between intrachain and interchain interactions in semiconducting polymer assemblies: The HJ-aggregate model journal May 2012
Experimental evidence that short-range intermolecular aggregation is sufficient for efficient charge transport in conjugated polymers journal August 2015
H- and J-Aggregate Behavior in Polymeric Semiconductors journal April 2014
Excitons in Conjugated Oligomer Aggregates, Films, and Crystals journal May 2006

Cited By (16)

Fully Conjugated Porphyrin Glass: Collective Light-Harvesting Antenna for Near-Infrared Fluorescence beyond 1 μm journal April 2018
Ultrafast bridge planarization in donor-π-acceptor copolymers drives intramolecular charge transfer journal November 2017
Chain length-dependent luminescence in acceptor-doped conjugated polymers journal August 2019
Bulk Heterojunction Solar Cells: Impact of Minor Structural Modifications to the Polymer Backbone on the Polymer-Fullerene Mixing and Packing and on the Fullerene-Fullerene Connecting Network journal January 2018
Hole-Transfer Dependence on Blend Morphology and Energy Level Alignment in Polymer: ITIC Photovoltaic Materials journal December 2017
Semiconducting Polymer Thin Films Used in Organic Solar Cells: A Scanning Tunneling Microscopy Study journal December 2018
Photoactive Blend Morphology Engineering through Systematically Tuning Aggregation in All-Polymer Solar Cells journal January 2018
In Situ Analysis of Solvent and Additive Effects on Film Morphology Evolution in Spin-Cast Small-Molecule and Polymer Photovoltaic Materials journal May 2018
Solution-Processable, Solid State Donor-Acceptor Materials for Singlet Fission journal September 2018
Polymersolarzellen: Fortschritt, Herausforderungen und Perspektiven journal March 2019
All-Polymer Solar Cells: Recent Progress, Challenges, and Prospects journal February 2019
Adjustment of the solid fluorescence of a chalcone derivative through controlling steric hindrance journal January 2017
Understanding the structure-determining solid fluorescence of an azaacene derivative journal January 2017
Organic electronics by design: the power of minor atomic and structural changes journal January 2018
Deconstructing the behavior of donor–acceptor copolymers in solution & the melt: the case of PTB7 journal January 2019
Aggregation control in natural brush-printed conjugated polymer films and implications for enhancing charge transport journal November 2017

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