skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Every Atom Counts: Elucidating the Fundamental Impact of Structural Change in Conjugated Polymers for Organic Photovoltaics

Journal Article · · Chemistry of Materials
 [1];  [2];  [3]; ORCiD logo [1]; ORCiD logo [4];  [5];  [3]; ORCiD logo [1];  [5]; ORCiD logo [1]; ORCiD logo [5]; ORCiD logo [4]; ORCiD logo [1]; ORCiD logo [3]; ORCiD logo [6]; ORCiD logo [1]
  1. Georgia Inst. of Technology, Atlanta, GA (United States). School of Chemistry and Biochemistry, Center for Organic Photonics and Electronics, Georgia Tech Polymer Network
  2. North Carolina State Univ., Raleigh, NC (United States). Dept. of Physics; Fayetteville State Univ., Fayetteville, NC (United States)
  3. Westfalische Wilhelms-Univ. Munster, Munster (Germany). Inst. of Physical Chemistry
  4. SLAC National Accelerator Lab., Menlo Park, CA (United States)
  5. North Carolina State Univ., Raleigh, NC (United States). Dept. of Materials Science and Engineering
  6. North Carolina State Univ., Raleigh, NC (United States). Dept. of Physics
+ Show Author Affiliations

As many conjugated polymer-based organic photovoltaic (OPV) materials provide substantial solar power conversion efficiencies (as high as 13%), it is important to develop a deeper understanding of how the primary repeat unit structures impact device performance. In this work, we have varied the group 14 atom (C, Si, Ge) at the center of a bithiophene fused ring to elucidate the impact of a minimal repeat unit structure change on the optical, transport, and morphological properties, which ultimately control device performance. Careful polymerization and polymer purification produced three “one-atom change” donor–acceptor conjugated alternating copolymers with similar molecular weights and dispersities. DFT calculation, absorption spectroscopy, and high-temperature solution 1H nuclear magnetic resonance (NMR) results indicate that poly(dithienosilole-alt-thienopyrrolodione), P(DTS-TPD), and poly(dithienogermole-alt-thienopyrrolodione), P(DTG-TPD) exhibit different rotational conformations when compared to poly(cyclopentadithiophene-alt-thienopyrrolodione), P(DTC-TPD). Solid-state 1H MAS NMR experiments reveal that the greater probability of the anticonformation in P(DTS-TPD) and P(DTG-TPD) prevail in the solid phase. The conformational variation seen in solution and solid-state NMR in turn affects the polymer stacking and intermolecular interaction. Two-dimension 1H-1H DQ-SQ NMR correlation spectra shows aromatic–aromatic correlations for P(DTS-TPD) and P(DTG-TPD), which on the other hand is absent for P(DTC-TPD). In a thin-film interchain packing study using grazing incidence wide-angle X-ray scattering (GIWAXS), we observe the π-face of the conjugated backbones of P(DTC-TPD) aligned edge-on to the substrate, whereas in contrast the π-faces of P(DTS-TPD) and P(DTG-TPD) align parallel to the surface. These differences in polymer conformations and backbone orientations lead to variations in the OPV performance of blends with the fullerene PC71BM, with the device containing P(DTC-TPD):PCBM having a lower fill factor and a lower power conversion efficiency. Ultrafast transient absorption spectroscopy shows the P(DTC-TPD):PCBM blend to have a more pronounced triplet formation from bimolecular recombination of initially separated charges. With a combination of sub-bandgap external quantum efficiency measurements and DFT calculations, we present evidence that the greater charge recombination loss is the result of a lower lying triplet energy level for P(DTC-TPD), leading to a higher rate of recombination and lower OPV device performance. In conclusion, importantly, this study ties ultimate photovoltaic performance to morphological features in the active films that are induced from the processing solution and are a result of minimal one-atom differences in polymer repeat unit structure.

Research Organization:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES); US Department of the Navy, Office of Naval Research (ONR)
Grant/Contract Number:
N00014-16-1-2520; N00014-17-1-2243; N00014-17-1-2242; AC02-76SF00515; N00014-17-1-2208
OSTI ID:
1462363
Journal Information:
Chemistry of Materials, Vol. 30, Issue 9; ISSN 0897-4756
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 35 works
Citation information provided by
Web of Science

References (86)

Donor–acceptor conjugated polymers based on multifused ladder-type arenes for organic solar cells journal January 2015
Molecular Design of Benzodithiophene-Based Organic Photovoltaic Materials journal June 2016
Fullerene-Free Polymer Solar Cells with over 11% Efficiency and Excellent Thermal Stability journal April 2016
Organic Solar Cells Based on a 2D Benzo[1,2- b :4,5- b ′]difuran-Conjugated Polymer with High-Power Conversion Efficiency journal September 2015
Organic Solar Cells Using a High-Molecular-Weight Benzodithiophene-Benzothiadiazole Copolymer with an Efficiency of 9.4% journal November 2014
Morphology Evolution in High-Performance Polymer Solar Cells Processed from Nonhalogenated Solvent journal May 2015
Highly efficient thieno[3,4-c]pyrrole-4,6-dione-based solar cells processed from non-chlorinated solvent journal February 2014
Bithiopheneimide–Dithienosilole/Dithienogermole Copolymers for Efficient Solar Cells: Information from Structure–Property–Device Performance Correlations and Comparison to Thieno[3,4- c ]pyrrole-4,6-dione Analogues journal October 2012
Dithienogermole As a Fused Electron Donor in Bulk Heterojunction Solar Cells journal July 2011
Synthesis and Photovoltaic Properties of Poly(dithieno[3,2- b :2′,3′- d ]germole) Derivatives journal September 2011
High Efficiency Air-Processed Dithienogermole-Based Polymer Solar Cells journal February 2015
High-efficiency inverted dithienogermole–thienopyrrolodione-based polymer solar cells journal December 2011
Conjugated polymers based on C, Si and N-bridged dithiophene and thienopyrroledione units: synthesis, field-effect transistors and bulk heterojunction polymer solar cells journal January 2011
Synthesis and characterization of a series of low-bandgap copolymers based on cyclopenta[2,1-b:3,4-b′]dithiophene and thienopyrroledione for photovoltaic applications journal July 2012
Suppression of Homocoupling Side Reactions in Direct Arylation Polycondensation for Producing High Performance OPV Materials journal December 2016
Recent progress in high efficiency polymer solar cells by rational design and energy level tuning of low bandgap copolymers with various electron-withdrawing units journal April 2016
Thieno[3,4- c ]pyrrole-4,6-dione-Based Polymers for Optoelectronic Applications journal November 2012
Linear Side Chains in Benzo[1,2- b :4,5- b ′]dithiophene–Thieno[3,4- c ]pyrrole-4,6-dione Polymers Direct Self-Assembly and Solar Cell Performance journal March 2013
Polymer solar cells with enhanced fill factors journal August 2013
Isoindigo, a Versatile Electron-Deficient Unit For High-Performance Organic Electronics journal September 2013
An Easily Accessible Isoindigo-Based Polymer for High-Performance Polymer Solar Cells journal September 2011
Isoindigo-based copolymers for polymer solar cells with efficiency over 7% journal January 2014
Dithienocarbazole and Isoindigo based Amorphous Low Bandgap Conjugated Polymers for Efficient Polymer Solar Cells journal October 2013
Isoindigo fluorination to enhance photovoltaic performance of donor–acceptor conjugated copolymers journal January 2014
High-Molecular-Weight Regular Alternating Diketopyrrolopyrrole-based Terpolymers for Efficient Organic Solar Cells journal June 2013
Chalcogenophene Comonomer Comparison in Small Band Gap Diketopyrrolopyrrole-Based Conjugated Polymers for High-Performing Field-Effect Transistors and Organic Solar Cells journal January 2015
Fluorinated Benzothiadiazole-Based Conjugated Polymers for High-Performance Polymer Solar Cells without Any Processing Additives or Post-treatments journal October 2013
Efficient Polymer Solar Cells Based on Benzothiadiazole and Alkylphenyl Substituted Benzodithiophene with a Power Conversion Efficiency over 8% journal July 2013
Aggregation and morphology control enables multiple cases of high-efficiency polymer solar cells journal November 2014
Well-controlled thieno[3,4-c]pyrrole-4,6-(5H)-dione based conjugated polymers for high performance organic photovoltaic cells with the power conversion efficiency exceeding 9% journal January 2015
Efficient inverted polymer solar cells employing favourable molecular orientation journal May 2015
Semi-crystalline photovoltaic polymers with efficiency exceeding 9% in a ∼300 nm thick conventional single-cell device journal January 2014
Prominent Short-Circuit Currents of Fluorinated Quinoxaline-Based Copolymer Solar Cells with a Power Conversion Efficiency of 8.0% journal December 2012
A low bandgap polymer based on isoindigo and bis(dialkylthienyl)benzodithiophene for organic photovoltaic applications journal August 2012
Single-junction polymer solar cells with high efficiency and photovoltage journal February 2015
Chemistry of the Aromatic 9-Germafluorenyl Dianion and Some Related Silicon and Carbon Species journal October 2002
Low bandgap semiconducting polymers for polymeric photovoltaics journal January 2016
Recent advances in high performance donor-acceptor polymers for organic photovoltaics journal July 2017
Batch-to-Batch Variation of Polymeric Photovoltaic Materials: its Origin and Impacts on Charge Carrier Transport and Device Performances journal July 2014
Strong polymer molecular weight-dependent material interactions: impact on the formation of the polymer/fullerene bulk heterojunction morphology journal January 2017
Effect of Polymer-Fullerene Interaction on the Dielectric Properties of the Blend journal February 2017
Germanium- and Silicon-Substituted Donor-Acceptor Type Copolymers: Effect of the Bridging Heteroatom on Molecular Packing and Photovoltaic Device Performance journal July 2014
Systematic Variation of Fluorinated Diketopyrrolopyrrole Low Bandgap Conjugated Polymers: Synthesis by Direct Arylation Polymerization and Characterization and Performance in Organic Photovoltaics and Organic Field-Effect Transistors journal September 2015
Making Ends Meet: Flow Synthesis as the Answer to Reproducible High-Performance Conjugated Polymers on the Scale that Roll-to-Roll Processing Demands journal February 2015
Structural and morphological effects of alkyl side chains on flanking thiophenes of diketopyrrolopyrrole polymers for organic photovoltaic devices journal September 2016
Pd 2 (dba) 3 as a Precursor of Soluble Metal Complexes and Nanoparticles: Determination of Palladium Active Species for Catalysis and Synthesis journal March 2012
Direct Arylation Polycondensation: A Promising Method for the Synthesis of Highly Pure, High-Molecular-Weight Conjugated Polymers Needed for Improving the Performance of Organic Photovoltaics journal February 2014
End Capping Does Matter: Enhanced Order and Charge Transport in Conjugated Donor–Acceptor Polymers journal September 2015
Role of trace impurities in the photovoltaic performance of solution processed small-molecule bulk heterojunction solar cells journal January 2012
Systematic Analysis of Polymer Molecular Weight Influence on the Organic Photovoltaic Performance journal September 2015
The Spectral Signatures of Frenkel Polarons in H- and J-Aggregates journal March 2010
Donor–acceptor stacking arrangements in bulk and thin-film high-mobility conjugated polymers characterized using molecular modelling and MAS and surface-enhanced solid-state NMR spectroscopy journal January 2017
Impact of Fluorine Substituents on π-Conjugated Polymer Main-Chain Conformations, Packing, and Electronic Couplings journal July 2016
Macroscopic Structural Compositions of π-Conjugated Polymers: Combined Insights from Solid-State NMR and Molecular Dynamics Simulations journal August 2017
A Strategy for Revealing the Packing in Semicrystalline π-Conjugated Polymers: Crystal Structure of Bulk Poly-3-hexyl-thiophene (P3HT) journal October 2012
Interplay of Structure and Dynamics in Functional Macromolecular and Supramolecular Systems As Revealed by Magnetic Resonance Spectroscopy journal August 2015
Sub-ns triplet state formation by non-geminate recombination in PSBTBT:PC 70 BM and PCPDTBT:PC 60 BM organic solar cells journal January 2015
Ambipolar Charge Transport in Isoindigo-Based Donor–Acceptor Polymers journal February 2016
Broadband Multiple-Quantum NMR Spectroscopy journal October 1996
Structure of Crystalline Phosphates from 31 P Double-Quantum NMR Spectroscopy journal January 1996
The use of a selective saturation pulse to suppress t 1 noise in two-dimensional 1 H fast magic angle spinning solid-state NMR spectroscopy journal November 2015
Solid-State NMR in Macromolecular Systems: Insights on How Molecular Entities Move journal March 2013
Columnar Packing Motifs of Functionalized Perylene Derivatives: Local Molecular Order Despite Long-Range Disorder journal April 2009
High-Resolution 1H NMR Spectroscopy in the Solid State: Very Fast Sample Rotation and Multiple-Quantum Coherences journal August 2001
An Investigation of π−π Packing in a Columnar Hexabenzocoronene by Fast Magic-Angle Spinning and Double-Quantum 1 H Solid-State NMR Spectroscopy journal July 1999
Dipolar recoupling in fast-MAS solid-state NMR spectroscopy journal September 2004
Ultrahigh Mobility in Polymer Field-Effect Transistors by Design journal March 2011
Probing the Relation Between Charge Transport and Supramolecular Organization Down to Ångström Resolution in a Benzothiadiazole-Cyclopentadithiophene Copolymer journal June 2012
Solid-State Organization and Ambipolar Field-Effect Transistors of Benzothiadiazole-Cyclopentadithiophene Copolymer with Long Branched Alkyl Side Chains journal June 2013
A general relationship between disorder, aggregation and charge transport in conjugated polymers journal August 2013
Solution-processed small molecule:fullerene bulk-heterojunction solar cells: impedance spectroscopy deduced bulk and interfacial limits to fill-factors journal January 2013
Effects of Shortened Alkyl Chains on Solution-Processable Small Molecules with Oxo-Alkylated Nitrile End-Capped Acceptors for High-Performance Organic Solar Cells journal July 2014
Quantification of Geminate and Non-Geminate Recombination Losses within a Solution-Processed Small-Molecule Bulk Heterojunction Solar Cell journal March 2012
Nongeminate Recombination and Charge Transport Limitations in Diketopyrrolopyrrole-Based Solution-Processed Small Molecule Solar Cells journal February 2013
Space-Charge Limited Photocurrent journal April 2005
Organic Solar Cell Efficiencies Under the Aspect of Reduced Surface Recombination Velocities journal November 2010
A New Approach for Probing the Mobility and Lifetime of Photogenerated Charge Carriers in Organic Solar Cells Under Real Operating Conditions journal July 2012
Low-Temperature Behaviour of Charge Transfer Excitons in Narrow-Bandgap Polymer-Based Bulk Heterojunctions journal May 2011
High-efficiency polymer solar cells with small photon energy loss journal December 2015
Photovoltaic Function and Exciton/Charge Transfer Dynamics in a Highly Efficient Semiconducting Copolymer journal July 2013
Charge generation and transport in efficient organic bulk heterojunction solar cells with a perylene acceptor journal January 2014
Quantitative Bimolecular Recombination in Organic Photovoltaics through Triplet Exciton Formation journal February 2014
Charge Carrier Generation Followed by Triplet State Formation, Annihilation, and Carrier Recreation in PBDTTT-C/PC 60 BM Photovoltaic Blends journal June 2015
The role of spin in the kinetic control of recombination in organic photovoltaics journal August 2013
Relating the open-circuit voltage to interface molecular properties of donor:acceptor bulk heterojunction solar cells journal March 2010
Optical, Electrical, and Magnetic Studies of Organic Solar Cells Based on Low Bandgap Copolymer with Spin ½ Radical Additives journal February 2015

Cited By (9)

Tuning the molecular geometry and packing mode of non-fullerene acceptors by altering the bridge atoms towards efficient organic solar cells journal January 2020
Donor Conjugated Polymers with Polar Side Chain Groups: The Role of Dielectric Constant and Energetic Disorder on Photovoltaic Performance journal October 2018
Intramolecular Energy Transfer in Dithienogermole Derivatives journal March 2019
Materials in Organic Electrochemical Transistors for Bioelectronic Applications: Past, Present, and Future journal December 2018
Unifying Energetic Disorder from Charge Transport and Band Bending in Organic Semiconductors journal March 2019
Direct comparison of dithienosilole and dithienogermole as π-conjugated linkers in photosensitizers for dye-sensitized solar cells journal January 2019
The effect of side-chain length on the microstructure and processing window of zone-cast naphthalene-based bispentalenes journal January 2019
Charge-transfer electronic states in organic solar cells journal September 2019
Over 13% Efficiency Ternary Nonfullerene Polymer Solar Cells with Tilted Up Absorption Edge by Incorporating a Medium Bandgap Acceptor journal September 2018

Similar Records

Related Subjects

36 MATERIALS SCIENCE