Morphology evolution via self-organization and lateral and vertical diffusion in polymer:fullerene solar cell blends
Source abstract
Abstract
Control of blend morphology at the microscopic scale is critical for optimizing the power conversion efficiency of plastic solar cells based on blends of conjugated polymer with fullerene derivatives. In the case of bulk heterojunctions of regioregular poly(3-hexylthiophene) (P3HT) and a soluble fullerene derivative ([6,6]-phenyl C61-butyric acid methyl ester, PCBM), both blend morphology and photovoltaic device performance are influenced by various treatments, including choice of solvent, rate of drying, thermal annealing and vapour annealing. Although the protocols differ significantly, the maximum power conversion efficiency values reported for the various techniques are comparable (4-5%). In this paper, we demonstrate that these techniques all lead to a common arrangement of the components, which consists of a vertically and laterally phase-separated blend of crystalline P3HT and PCBM. We propose a morphology evolution that consists of an initial crystallization of P3HT chains, followed by diffusion of PCBM molecules to nucleation sites, at which aggregates of PCBM then grow.
Source: europepmc · Quality: candidate unverified · Source record ↗
Research context
OpenAlex topics: Organic Electronics and Photovoltaics · Conducting polymers and applications · Carbon Nanotubes in Composites
SciVX discovery tags are terminology-based. OpenAlex topics are source-provided classifications.
References (45)
Show source-provided references
1. Halls, J. J. M. et al. Efficient photodiodes from interpenetrating networks. Nature 376, 498–500 (1995).10.1038/376498a0 ↗
2. Yu, G., Gao, J., Hummelen, J. C., Wudl, F. & Heeger, A. J. Polymer photovoltaic cells: Enhanced efficiencies via a network of internal donor–acceptor heterojunctions. Science 270, 1789–1791 (1995).10.1126/science.270.5243.1789 ↗
3. Hoppe, H. & Sariciftci, N. S. Morphology of polymer/fullerene bulk heterojunction solar cells. J. Mater. Chem. 16, 45–61 (2006).10.1039/B510618B ↗
4. Shaheen, S. E. et al. 2.5% efficient organic plastic solar cells. Appl. Phys. Lett. 78, 841–843 (2001).10.1063/1.1345834 ↗
5. Ma, W., Yang, C., Gong, X., Lee, K. & Heeger, A. J. Thermally stable, efficient polymer solar cells with nanoscale control of the interpenetrating network morphology. Adv. Funct. Mater. 15, 1617–1622 (2005).10.1002/adfm.200500211 ↗
6. Reyes-Reyes, M., Kim, K. & Carroll, D. L. High-efficiency photovoltaic devices based on annealed poly(3-hexylthiophene and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6) C61 blends. Appl. Phys. Lett. 87, 083506 (2005).10.1063/1.2006986 ↗
7. Kim, Y. et al. A strong regioregularity effect in self-organizing conjugated polymer films and high-efficiency polythiophene:fullerene solar cells. Nature Mater. 5, 197–203 (2006).10.1038/nmat1574 ↗
8. Li, G. et al. High-efficiency solution processable polymer photovoltaic cells by self-organization of polymer blends. Nature Mater. 4, 864–868 (2005).10.1038/nmat1500 ↗
9. Kim, Y. et al. Device annealing effect in organic solar cells with blends of regioregular poly(3-hexylthiophene) and soluble fullerene. Appl. Phys. Lett. 86, 063502 (2005).10.1063/1.1861123 ↗
10. Vanlaeke, P. et al. Polythiophene based bulk heterojunction solar cells: Morphology and its implications. Thin Solid Films 511–512, 358–361 (2006).10.1016/j.tsf.2005.12.031 ↗
11. Mihailetchi, V. D. et al. Origin of the enhanced performance in poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester solar cells upon slow drying of the active layer. Appl. Phys. Lett. 89, 012107 (2006).10.1063/1.2212058 ↗
12. Kim, K., Liu, J. & Carroll, D. L. Thermal diffusion processes in bulk heterojunction formation from poly-3-hexylthiophene/C60 single heterojunction photovoltaics. Appl. Phys. Lett. 88, 181911 (2006).10.1063/1.2199970 ↗
13. Chirvase, D., Parisi, J., Hummelen, J. C. & Dyakonov, V. Influence of nanomorphology on the photovoltaic action of polymer–fullerene composites. Nanotechnology 15, 1317–1323 (2004).10.1088/0957-4484/15/9/035 ↗
14. Zhao, Y., Xie, Z., Qu, Y., Geng, Y. & Wang, L. Solvent-vapor treatment induced performance enhancement of poly(3-hexylthiophene):methanofullerene bulk-heterojunction photovoltaic cells. Appl. Phys. Lett. 90, 043504 (2007).10.1063/1.2434173 ↗
15. Osterbacka, R., An, C. P., Jiang, X. M. & Vardeny, Z. V. Two-dimensional electronic excitations in self-assembled conjugated polymer nanocrystals. Science 287, 839–842 (2000).10.1126/science.287.5454.839 ↗
16. Zhokhavets, V., Erb, T., Gobsch, G., Al-Ibrahim, M. & Ambacher, O. Relation between absorption and crystallinity of poly(3-hexylthiophene)/fullerene films for plastic solar cells. Chem. Phys. Lett. 418, 347–350 (2006).10.1016/j.cplett.2005.11.020 ↗
17. Vanlaeke, P. et al. P3HT/PCBM bulk heterojunction solar cells: Relation between morphology and electro-optical characteristics. Sol. Energy Mater. Sol. Cells 90, 2150–2158 (2006).10.1016/j.solmat.2006.02.010 ↗
18. Klimov, E., Li, W., Yang, X., Hoffmann, G. G. & Loos, J. Scanning near-field and confocal Raman microscopic investigation of P3HT-PCBM systems for solar cell applications. Macromolecules 39, 4493–4496 (2006).10.1021/ma052590x ↗
19. Yang, X. et al. Nanoscale morphology of high-performance polymer solar cell. Nano Lett. 5, 579–583 (2005).10.1021/nl048120i ↗
20. Zhokhavets, V., Erb, T., Hoppe, H., Gobsch, G. & Sariciftci, N. S. Effect of annealing of poly(3-hexylthiophene)/fullerene bulk heterojunction composites on structural and optical properties. Thin Solid Films 496, 679–682 (2006).10.1016/j.tsf.2005.09.093 ↗
21. Savenije, T. J., Kroeze, J. E., Yang, X. & Loos, J. The effect of thermal treatment on the morphology and change carrier dynamics in a polythiophene-fullerene bulk heterojunction. Adv. Funct. Mater. 15, 1260–1266 (2005).10.1002/adfm.200400559 ↗
22. Swinnen, A. et al. Tuning the dimensions of C60-based needlelike crystals in blended thin films. Adv. Funct. Mater. 16, 760–765 (2006).10.1002/adfm.200500812 ↗
23. Yang, X., Alexeev, A., Michels, A. J. & Loos, J. Effect of spatial confinement on the morphology evolution of thin poly(p-phenylenevinylene)/methanofullerene composite films. Macromolecules 38, 42890–4295 (2005).
24. Tompkins, H. G. & Irene, E. A. (eds) Handbook of Ellipsometry (William Andrew Publishing, Norwich, New York, 2005).10.1007/3-540-27488-X ↗
25. Fried, M. et al. Dose-dependence of ion implantation-caused damage in silicon measured by ellipsometry and backscattering spectrometry. Thin Solid Films 455, 404–409 (2004).10.1016/j.tsf.2004.01.027 ↗
26. Zaumseil, P., Krüger, D., Kurps, R., Fursenko, O. & Formanek, P. Precise measurement of Ge depth profiles in SiGe HBT’s—a comparison of different methods. Solid State Phenom. 95–96, 473–482 (2004).
27. Reyes-Reyes, M. et al. Meso-structure formation for enhanced organic photovoltaic cells. Org. Lett. 7, 5749–5752 (2005).10.1021/ol051950y ↗
28. Waldauf, C. et al. Highly efficient inverted organic photovoltaics using solution based titanium oxide as electron selective contact. Appl. Phys. Lett. 89, 233517 (2006).10.1063/1.2402890 ↗
29. Goffri, S. et al. Multicomponent semiconducting polymer systems with low crystallization-induced percolation threshold. Nature Mater. 5, 950–956 (2006).10.1038/nmat1779 ↗
30. Arias, A. C. et al. Vertically segregated polymer-blend photovoltaic thin-film structures through surface-mediated solution processing. Appl. Phys. Lett. 80, 1694–1697 (2002).10.1063/1.1456550 ↗
31. Björnström, C. M. et al. Multilayer formation in spin-coated thin films of low-bandgap polyfluorene:PCBM blends. J. Phys. Condens. Matter 17, L529–L534 (2005).10.1088/0953-8984/17/50/L01 ↗
32. Björnström, C. M. et al. Vertical phase separation in spin-coated films of a low bandgap polyfluorene/PCBM blend—effects of specific substrate interaction. Appl. Surf. Sci. 253, 3906–3912 (2007).10.1016/j.apsusc.2006.08.024 ↗
33. Heriot, S. Y. & Jones, R. A. L. An interfacial instability in a transient wetting layer leads to lateral phase separation in thin spin-cast polymer-blend films. Nature Mater. 4, 782–786 (2005).10.1038/nmat1476 ↗
34. Snaith, H. J., Greenham, N. C. & Friend, R. H. The origin of collected charge and open-circuit voltage in blended polyfluorene photovoltaic devices. Adv. Mater. 16, 1640–1645 (2004).10.1002/adma.200305766 ↗
35. Xue, J., Rand, B. P., Uchida, S. & Forrest, S. R. Mixed donor–acceptor molecular heterojunctions for photovoltaic applications. II. Devices performance. J. Appl. Phys. 98, 124903 (2005).10.1063/1.2142073 ↗
36. Heutz, S., Sullivan, P., Sanderson, B. M., Schultes, S. M. & Jones, T. S. Influence of molecular architecture and intermixing on the photovoltaic, morphological and spectroscopic properties of CuPc–C60 heterojunctions. Sol. Energy Mater. Sol. Cells 83, 229–245 (2004).10.1016/j.solmat.2004.02.027 ↗
37. Sims, M. et al. On the use of optical probes to monitor the thermal transitions in spin-coated poly(9,9-dioctylfluorene) films. J. Phys. Condens. Matter 17, 1–12 (2005).10.1088/0953-8984/17/41/002 ↗
38. Kim, H., So, W.-W. & Moon, S.-J. Effect of thermal annealing on the performance of P3HT/PCBM polymer photovoltaic cells. J. Kor. Phys. Soc. 48, 441–445 (2006).
39. Si, L., Massa, M. V., Dalnoki-Veress, K., Brown, H. R. & Jones, R. A. L. Chain entanglement in thin freestanding polymer films. Phys. Rev. Lett. 94, 127801 (2005).10.1103/PhysRevLett.94.127801 ↗
40. Ellison, C. J. & Torkelson, J. M. The distribution of glass-transition temperatures in nanoscopically confined glass formers. Nature Mater. 2, 695–700 (2003).10.1038/nmat980 ↗
41. Sharp, J. S. & Forrest, J. A. Free surfaces cause reductions in the glass transition temperature of thin polystyrene films. Phys. Rev. Lett. 91, 235701 (2003).10.1103/PhysRevLett.91.235701 ↗
42. Campoy-Quiles, M., Sims, M., Etchegoin, P. G. & Bradley, D. D. C. Thickness-dependent thermal transition temperatures in thin conjugated polymer films. Macromolecules 39, 7673–7680 (2006).10.1021/ma0605752 ↗
43. van Zanten, J. H., Wallace, W. E. & Wu, W.-L. Effect of strongly favourable substrate interaction on the thermal properties of ultrathin polymer films. Phys. Rev. E 53, R2053–R2056 (1996).10.1103/PhysRevE.53.R2053 ↗
44. Hummelen, J. C. et al. Preparation and characterization of fulleroid and methanofullerene derivatives. J. Org. Chem. 60, 532–538 (1995).10.1021/jo00108a012 ↗
45. Campoy-Quiles, M. et al. Ellipsometric characterization of the optical constants of polyfluorene gain media. Adv. Funct. Mater. 15, 925–933 (2005).10.1002/adfm.200400121 ↗