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Ching-I Huang Zong-Hua Yu and Yi-Kang Lan National Taiwan University

Ching-I Huang Zong-Hua Yu and Yi-Kang Lan National Taiwan University Institute of Polymer Science and Engineering July 6, 2011. A Theoretical Approach to the Molecular Conformation, Packing Structure, and Charge Transfer Behavior in the Poly-3-hexylthiophene (P3HT) and Derivatives.

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Ching-I Huang Zong-Hua Yu and Yi-Kang Lan National Taiwan University

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  1. Ching-I Huang Zong-Hua Yu and Yi-Kang Lan National Taiwan University Institute of Polymer Science and Engineering July 6, 2011 A Theoretical Approach to the Molecular Conformation, Packing Structure, and Charge Transfer Behavior in the Poly-3-hexylthiophene (P3HT) and Derivatives (Initiated by collaboration with experimental groups at NTU through a National Nanotechnology Program: Prof. W. C. Chen and L. Y. Wang) International Conference on the Hierarchical Structures in Complex Fluids Beijing, China

  2. Potential Applications of Conducting Polymers Solar cell • High carrier mobility. • Low threshold voltage. • High On/Off ratio. • Thermal stability. • Broad absorption. • High Power-conversion efficiency (PSE). • Low bandgap. • Avoid electron-hole recombination. Alternating donor-acceptor copolymers or Side chain-conjugated polymers are adopted. Chem. Mater., 2010, 22, 10. J Polym. Res., 2009, 16, 239. http://www.ucsusa.org

  3. New P3HT-Based Side Chain-Conjugated Polymers Normalized UV–Vis absorption spectra of P1, P2, and P3HT in as thin films Broader absorption Higher hole mobility Yuet al., Solar Energy Materials & Solar Cells.2009, 93, 613.

  4. Molecular Weight Processing Regularity Conjugation Length in the Side-Chain Objectives Packing Orientation Chain Conformation Absorption Spectra Charge Mobility 1. Thoroughly understand the charge transfer mechanism correlated with the molecular conformation in the ordered states at various lengths of conjugated side chain. 2. Correlate the current experimental results in the P3HT and P3HT-based side chain conjugated polymers. (P3HT: J. Phys. Chem. B, 2009, 113, 14555. J. Phys. Chem. B, 2008, 112, 14857.)

  5. Simulated Systems: P3HT and A1-A4 P3HT Increasing the conjugation length in the side chain A1 A2 A3 A4

  6. Simulations Ordered state of initial structure in various regularity/temp. Initial structure Vacuum state of initial structure in various regularity/temp. Intra- and Inter-chain Charge Mobility Initial Segment

  7. Ordered Packing Structures of P3HT rr = 100% 300K 180 ° 180° O The thiophene rings in the main chains are typically in a coplanar conformation. J. Phys. Chem. B, 2009, 113, 14555. J. Phys. Chem. B, 2008, 112, 14857.

  8. Ordered Packing Structures of A1 Projection along a axis α = 49.62° O Projection along c axis 3.65 Å Projection along b axis 25.15Å β= 87.61° O O O γ= 94.42°

  9. Ordered Packing Structures of A2 Projection along a axis α = 63.23° O Projection along c axis 3.94 Å Projection along b axis 28.12Å O O β= 90° O γ= 90°

  10. Ordered Packing Structures of A3 Projection along a axis O Projection along c axis α = 63.79° 3.94 Å Projection along b axis 36.54Å β= 90° O O O γ= 90°

  11. Ordered Packing Structures of A4 Projection along a axis O 3.82 Å α =115.71° 36.54Å Projection along c axis O γ= 89.34° O

  12. Cell Parameters for P3HT and A1-A4

  13. The snapshots for conjugated side chains of A1-A4 A1 A2 4.5Å 4.6Å 4.5Å A3 A4 4.3Å 3.8Å 4.3Å 4.4Å 4.2Å 4.4Å 4.4Å 1. The thiophene rings in the main chains are typically in co-planar. 2. But the thiophene side chains are not in coplanar with respect to the thiophene main chains. 3. The thiophene side chains are in a parallel packing within π – π interactions.

  14. Analysis of Torsional Angles between Two Thiophenes τmain-chain 180 ° 180° Similar to P3HT, the thiophene rings in the main chains are typically in co-planar.

  15. Analysis of Torsional Angles between Two Thiophenes τside1 180° A deviation of 60° out of 180° is found to be the optimized geometry of the adjacent segments (energetically favorable). 360 ° 180° 360 °

  16. The torsional angle of side chain τside3 τside2 τside4

  17. Two State Hopping Model

  18. Einstein relation Semi-classical Marcus theory λ = λ1+λ2 = (Eion-Eneu)+( E+ion- E+neu)

  19. Within the ordered lamellae for P3HT Intrachain Interchain MP2/6-311G(d,p) Intrachain >> Interchain 2~3 Orders 19 J. Phys. Chem. B, 2009, 113, 14555. J. Phys. Chem. B, 2008, 112, 14857.

  20. Charge Transfer through P3HT Nanofibril Transport along Interchain Fiber axis ~0.01 cm2/Vs Merlo, J. A. ; Frisbie ,C. D. J. Phys. Chem. B ,2004, 108, 19169. Merlo, J. A. ; Frisbie ,C. D. J. Poly. Sci. B, 2003, 41, 2674.

  21. Within the ordered lamellae for P3HT and A1 Intrachain Interchain With increasing the conjugation length in the side chain, the hole mobility along the intra-chain direction decreases, but it increases along the inter-chain direction.

  22. Summary We have thoroughly analyzed the molecular conformation, packing structure, and charge transfer behavior for P3HT and P3HT-based side chain-conjugated systems. Due to the π – π interactions along the interchain directions, the thiophene rings in the main-chain tend to keep a coplanar conformation and pack well regardless of the presence of thiophene side-chain. The thiophene side chains are in a parallel packing within π – π interaction distances. The thiophene side-chains are not in coplanar with respect to the thiophene main-chains. (a deviation of 60° out of coplanarity)

  23. Summary With increasing the conjugation length (number of thiophines) in the side-chain  π – π stacking in the side-chain↑ mobility along the π – π interchain direction↑ mobility along the main-chain direction↓ light absorption ? 5. What about alternating donor-acceptor copolymers?

  24. Thanks for your attention Q and A

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