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Quantitative relations between interaction parameter, miscibility and function in organic solar cells

Nature Materials volume 17, pages 253–260 (2018)Cite this article

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Abstract

Although it is known that molecular interactions govern morphology formation and purity of mixed domains of conjugated polymer donors and small-molecule acceptors, and thus largely control the achievable performance of organic solar cells, quantifying interaction–function relations has remained elusive. Here, we first determine the temperature-dependent effective amorphous–amorphous interaction parameter, χaa(T), by mapping out the phase diagram of a model amorphous polymer:fullerene material system. We then establish a quantitative ‘constant-kink-saturation’ relation between χaa and the fill factor in organic solar cells that is verified in detail in a model system and delineated across numerous high- and low-performing materials systems, including fullerene and non-fullerene acceptors. Our experimental and computational data reveal that a high fill factor is obtained only when χaa is large enough to lead to strong phase separation. Our work outlines a basis for using various miscibility tests and future simulation methods that will significantly reduce or eliminate trial-and-error approaches to material synthesis and device fabrication of functional semiconducting blends and organic blends in general.

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Fig. 1: Schematic morphologies and phase diagram of an amorphous model system.
Fig. 2: Quantitative relation of χaa(T) to device performance and morphology in a model system.
Fig. 3: MD simulations of PCDTBT:PCBM.
Fig. 4: Relation of χaa(T) to morphology and device FF in many systems.

References

  1. Brédas, J.-L., Norton, J. E., Cornil, J. & Coropceanu, V. Molecular understanding of organic solar cells: the challenges. Acc. Chem. Res. 42, 1691–1699 (2009).

    Google Scholar 

  2. Huang, Y., Kramer, E. J., Heeger, A. J. & Bazan, G. C. Bulk heterojunction solar cells: morphology and performance relationships. Chem. Rev. 114, 7006–7043 (2014).

    CAS  Google Scholar 

  3. Zhao, J. et al. Efficient organic solar cells processed from hydrocarbon solvents. Nat. Energy 1, 15027 (2016).

    CAS  Google Scholar 

  4. Li, S. et al. Energy-level modulation of small-molecule electron acceptors to achieve over 12% efficiency in polymer solar cells. Adv. Mater. 28, 9423–9429 (2016).

    CAS  Google Scholar 

  5. Ye, L. et al. High-efficiency nonfullerene organic solar cells: critical factors that affect complex multi-length scale morphology and device performance. Adv. Energy Mater. 7, 1602000 (2017).

    Google Scholar 

  6. Baran, D. et al. Reducing the efficiency-stability-cost gap of organic photovoltaics with highly efficient and stable small molecule acceptor ternary solar cells. Nat. Mater. 16, 363–369 (2017).

    CAS  Google Scholar 

  7. Zhao, F. et al. Single-junction binary-blend nonfullerene polymer solar cells with 12.1% efficiency. Adv. Mater. 29, 1700144 (2017).

    Google Scholar 

  8. Müller, C. et al. Binary organic photovoltaic blends: a simple rationale for optimum compositions. Adv. Mater. 20, 3510–3515 (2008).

    Google Scholar 

  9. Kouijzer, S. et al. Predicting morphologies of solution processed polymer:fullerene blends. J. Am. Chem. Soc. 135, 12057–12067 (2013).

    CAS  Google Scholar 

  10. Wolfer, P. et al. Identifying the optimum composition in organic solar cells comprising non-fullerene electron acceptors. J. Mater. Chem. A 1, 5989–5995 (2013).

    CAS  Google Scholar 

  11. Treat, N. D. et al. Polymer-fullerene miscibility: a metric for screening new materials for high-performance organic solar cells. J. Am. Chem. Soc. 134, 15869–15879 (2012).

    CAS  Google Scholar 

  12. Roland, S. et al. Fullerene-free polymer solar cells with highly reduced bimolecular recombination and field-independent charge carrier generation. J. Phys. Chem. Lett. 5, 2815–2822 (2014).

    CAS  Google Scholar 

  13. Ye, L. et al. Control of mesoscale morphology and photovoltaic performance in diketopyrrolopyrrole-based small band gap terpolymers. Adv. Energy Mater. 7, 1601138 (2017).

    Google Scholar 

  14. Mukherjee, S., Proctor, C. M., Bazan, G. C., Nguyen, T. Q. & Ade, H. Significance of average domain purity and mixed domains on the photovoltaic performance of high-efficiency solution-processed small-molecule BHJ solar cells. Adv. Energy Mater. 5, 1500877 (2015).

    Google Scholar 

  15. Bates, F. S. Polymer-polymer phase behavior. Science 251, 898–905 (1991).

    CAS  Google Scholar 

  16. Russell, T. P., Hjelm, R. P. & Seeger, P. A. Temperature dependence of the interaction parameter of polystyrene and poly(methyl methacrylate). Macromolecules 23, 890–893 (1990).

    CAS  Google Scholar 

  17. Leman, D. et al In situ characterization of polymer–fullerene bilayer stability. Macromolecules 48, 383–392 (2015).

    CAS  Google Scholar 

  18. Li, N. et al. Abnormal strong burn-in degradation of highly efficient polymer solar cells caused by spinodal donor-acceptor demixing. Nat. Commun. 8, 14541 (2017).

    CAS  Google Scholar 

  19. Lyons, B. P., Clarke, N. & Groves, C. The relative importance of domain size, domain purity and domain interfaces to the performance of bulk-heterojunction organic photovoltaics. Energy Environ. Sci. 5, 7657–7663 (2012).

    CAS  Google Scholar 

  20. Liu, F. et al. Molecular weight dependence of the morphology in P3HT:PCBM solar cells. ACS Appl. Mater. Interfaces 6, 19876–19887 (2014).

    CAS  Google Scholar 

  21. Bin, H. et al. 9.73% efficiency nonfullerene all organic small molecule solar cells with absorption-complementary donor and acceptor. J. Am. Chem. Soc. 139, 5085–5094 (2017).

    CAS  Google Scholar 

  22. Ghasemi, M. et al. Panchromatic sequentially cast ternary polymer solar cells. Adv. Mater. 29, 1604603 (2017).

    Google Scholar 

  23. Westacott, P. et al. Origin of fullerene-induced vitrification of fullerene:donor polymer photovoltaic blends and its impact on solar cell performance. J. Mater. Chem. A 5, 2689–2700 (2017).

    CAS  Google Scholar 

  24. Park, S. H. et al. Bulk heterojunction solar cells with internal quantum efficiency approaching 100%. Nat. Photon-. 3, 297–302 (2009).

    CAS  Google Scholar 

  25. Peters, C. H. et al. High efficiency polymer solar cells with long operating lifetimes. Adv. Energy Mater. 1, 491–494 (2011).

    CAS  Google Scholar 

  26. Gélinas, S. et al. Ultrafast long-range charge separation in organic semiconductor photovoltaic diodes. Science 343, 512–516 (2014).

    Google Scholar 

  27. Mukherjee, S. et al. Importance of domain purity and molecular packing in efficient solution-processed small-molecule solar cells. Adv. Mater. 27, 1105–1111 (2015).

    CAS  Google Scholar 

  28. Albrecht, S. et al. Quantifying charge extraction in organic solar cells: the case of fluorinated PCPDTBT. J. Phys. Chem. Lett. 5, 1131–1138 (2014).

    CAS  Google Scholar 

  29. Ro, H. W. et al Poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester mixing in organic solar cells. Macromolecules 45, 6587–6599 (2012).

    CAS  Google Scholar 

  30. Eitouni, H. B. & Balsara, N. P. in Physical Properties of Polymers Handbook (ed. Mark, J. E.) 339–356 (Springer, New York, 2007).

  31. Synooka, O. et al. Influence of thermal annealing on PCDTBT:PCBM composition profiles. Adv. Energy Mater. 4, 1300981 (2014).

    Google Scholar 

  32. Gann, E. et al. Soft x-ray scattering facility at the Advanced Light Source with real-time data processing and analysis. Rev. Sci. Instrum. 83, 045110 (2012).

    CAS  Google Scholar 

  33. Kozub, D. R. et al. Polymer crystallization of partially miscible polythiophene/fullerene mixtures controls morphology. Macromolecules 44, 5722–5726 (2011).

    CAS  Google Scholar 

  34. Helfand, E. & Tagami, Y. Theory of the interface between immiscible polymers. II. J. Chem. Phys. 56, 3592–3601 (1972).

    CAS  Google Scholar 

  35. Roe, R.-J. Methods of X-ray and Neutron Scattering in Polymer Science (Oxford Univ. Press, Oxford, 2000).

    Google Scholar 

  36. Nishi, T. & Wang, T. T. Melting point depression and kinetic effects of cooling on crystallization in poly(vinylidene fluoride)-poly(methyl methacrylate) mixtures. Macromolecules 8, 909–915 (1975).

    CAS  Google Scholar 

  37. Li, Z. et al. Donor polymer design enables efficient non-fullerene organic solar cells. Nat. Commun. 7, 13094 (2016).

    CAS  Google Scholar 

  38. Nielsen, C. B., Holliday, S., Chen, H.-Y., Cryer, S. J. & McCulloch, I. Non-fullerene electron acceptors for use in organic solar cells. Acc. Chem. Res. 48, 2803–2812 (2015).

    CAS  Google Scholar 

  39. Meng, D. et al. High-performance solution-processed non-fullerene organic solar cells based on selenophene-containing perylene bisimide acceptor. J. Am. Chem. Soc. 138, 375–380 (2016).

    CAS  Google Scholar 

  40. Stoltzfus, D. M., Clulow, A. J., Jin, H., Burn, P. L. & Gentle, I. R. Impact of dimerization on phase separation and crystallinity in bulk heterojunction films containing non-fullerene acceptors. Macromolecules 49, 4404–4415 (2016).

    CAS  Google Scholar 

  41. Staniec, P. A. et al. The nanoscale morphology of a PCDTBT:PCBM photovoltaic blend. Adv. Energy Mater. 1, 499–504 (2011).

    CAS  Google Scholar 

  42. Li, Z. et al. Toward improved lifetimes of organic solar cells under thermal stress: substrate-dependent morphological stability of PCDTBT:PCBM films and devices. Sci. Rep. 5, 15149 (2015).

    CAS  Google Scholar 

  43. Bartelt, J. A. et al. The importance of fullerene percolation in the mixed regions of polymer-fullerene bulk heterojunction solar cells. Adv. Energy Mater. 3, 364–374 (2013).

    CAS  Google Scholar 

  44. Ho, C. H. Y. et al. Using ultralow dosages of electron acceptor to reveal the early stage donor–acceptor electronic interactions in bulk heterojunction blends. Adv. Energy Mater. 7, 1602360 (2017).

    Google Scholar 

  45. van Franeker, J. J., Turbiez, M., Li, W., Wienk, M. M. & Janssen, R. A. A real-time study of the benefits of co-solvents in polymer solar cell processing. Nat. Commun. 6, 6229 (2015).

    Google Scholar 

  46. Dudowicz, J. & Freed, K. F. Effect of monomer structure and compressibility on the properties of multicomponent polymer blends and solutions: 1. Lattice Clust. Theory Compress. Syst. Macromol. 24, 5076–5095 (1991).

    CAS  Google Scholar 

  47. Aarts, D. G. A. L., Tuinier, R. & Lekkerkerker, H. N. W. Phase behaviour of mixtures of colloidal spheres and excluded-volume polymer chains. J. Phys. Condens. Matter 14, 7551 (2002).

    CAS  Google Scholar 

  48. Mutch, K. J., van Duijneveldt, J. S. & Eastoe, J. Colloid-polymer mixtures in the protein limit. Soft Matter 3, 155–167 (2007).

    CAS  Google Scholar 

  49. Nikolka, M. et al. High operational and environmental stability of high-mobility conjugated polymer field-effect transistors through the use of molecular additives. Nat. Mater. 16, 356–362 (2017).

    CAS  Google Scholar 

  50. Kilcoyne, A. L. D. et al. Interferometer-controlled scanning transmission X-ray microscopes at the Advanced Light Source. J. Synchrotron Radiat. 10, 125–136 (2003).

    CAS  Google Scholar 

  51. Hexemer, A. et al. A SAXS/WAXS/GISAXS beamline with multilayer monochromator. J. Phys. Conf. Ser. 247, 012007 (2010).

    Google Scholar 

  52. Plimpton, S. Fast parallel algorithms for short-range molecular dynamics. J. Comput. Phys. 117, 1–19 (1995).

    CAS  Google Scholar 

  53. Jackson, N. E. et al. Conformational order in aggregates of conjugated polymers. J. Am. Chem. Soc. 137, 6254–6262 (2015).

    CAS  Google Scholar 

  54. Jorgensen, W. L. & Tirado-Rives, J. The OPLS [optimized potentials for liquid simulations] potential functions for proteins, energy minimizations for crystals of cyclic peptides and crambin. J. Am. Chem. Soc. 110, 1657–1666 (1988).

    CAS  Google Scholar 

  55. Rathi, P., Huang, T.-M., Dayal, P. & Kyu, T. Crystalline−amorphous interaction in relation to the phase diagrams of binary polymer blends containing a crystalline constituent. J. Phys. Chem. B. 112, 6460–6466 (2008).

    CAS  Google Scholar 

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Acknowledgements

Work by NCSU was initiated with support from the US Department of Energy, Office of Science, Basic Energy Science, Division of Materials Science and Engineering under contract DE-FG02-98ER45737, and completed with support from ONR grants N00141512322 and N000141712204. X-ray data were acquired at beamlines 11.0.1.2, 7.3.3 and 5.3.2.2 at the Advanced Light Source, which is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract DE-AC02-05CH11231. The DSC instrument, and DSC and SIMS analysis by NCSU, were supported by a UNC General Administration Research Opportunity Initiative grant. SIMS was performed at the Analytical Instrumentation Facility (AIF) at NCSU, which is partially supported by the State of North Carolina and the National Science Foundation (award number ECCS-1542015). The AIF is a member of the North Carolina Research Triangle Nanotechnology Network (RTNN), a site in the National Nanotechnology Coordinated Infrastructure (NNCI). The work was partially supported by the National Basic Research Program of China (973 Program; 2013CB834705), HK JEBN Limited (Hong Kong), the Hong Kong Research Grants Council (T23-407/13-N, N_HKUST623/13 and 606012), HKUST President’s Office through the SSTSP scheme (project reference number: EP201) and the National Natural Science Foundation of China (NSFC, 21374090, 21504066, 21534003 and 51320105014). The work at KAUST was supported by generous KAUST internal funding. The work at Georgia Tech was funded by ONR grant N00014-17-1-2208. A.L.D. Kilcoyne, E. Schaible, C. Zhu, A. Hexemer, C. Wang and A. Young of the ALS (DOE) assisted with the measurements and provided instrument maintenance. S. Mukherjee and O. Awartani are acknowledged for assisting with part of the X-ray data acquisition and normalization, and C. McNeill is acknowledged for initial work on the STXM miscibility measurement of PCDTBT. The KAUST IT Research Computing Team and the KAUST Supercomputing Laboratory are acknowledged for providing computational resources. The authors acknowledge and appreciate the fruitful discussions with N. Stingelin, J. Michels, E. Gomez, and M. Balik, and thank A. Dinku for maintaining the shared device fabrication facilities at NCSU, and E. Gomez for sharing his FH code.

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Author notes

  1. Brian A Collins

    Present address: Department of Physics and Astronomy, Washington State University, Pullman, WA, USA

  2. L. Ye, H. Hu and M. Ghasemi contributed equally to this work.

Authors and Affiliations

  1. Department of Physics and ORaCEL, North Carolina State University, Raleigh, NC, USA

    Long Ye, Masoud Ghasemi, Brian A Collins, Joo-Hyun Kim, Joshua H. Carpenter, Terry McAfee & Harald Ade

  2. Department of Chemistry and Energy Institute, The Hong Kong University of Science and Technology, Kowloon, Hong Kong, China

    Huawei Hu, Kui Jiang, Zhengke Li, Jingbo Zhao, Joshua Lin Yuk Lai, Tingxuan Ma & He Yan

  3. Physical Science and Engineering Division, KAUST Solar Center, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia

    Tonghui Wang, Hong Li, Xiankai Chen & Jean-Luc Bredas

  4. School of Chemistry and Biochemistry & Center for Organic Photonics and Electronics (COPE), Georgia Institute of Technology, Atlanta, GA, USA

    Tonghui Wang, Hong Li, Xiankai Chen & Jean-Luc Bredas

  5. HKUST-Shenzhen Research Institute, Nanshan, Shenzhen, China

    Kui Jiang & He Yan

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Contributions

H.A. conceived the scientific framework and designed the experiments with the help of L.Y., M.G., H.H., H.Y. and J.-H.K. H.Y. initiated the study on various semi-crystalline polymer:SMA systems. H.H. made those polymer materials that were not purchased and carried out initial DSC measurements. M.G. performed DSC measurement of the PCDTBT:PCBM model system, additional DSC measurements of some semi-crystalline systems, and the SIMS measurements. L.Y. proposed the model PCDTBT system and carried out χaa–ISI–FF modelling, some DSC tests, device and R-SoXS experiments on the model system, and most of the final R-SoXS analysis. L.Y. and M.G. carried out the χaa(T) analysis. K.J. made and measured the polymer:SMA devices. J.C., J.-H.K. and T.M. acquired and analysed the initial R-SoXS data and measured materials density. B.A.C. and L.Y. acquired and analysed the STXM miscibility data. J.Y.L.L., J.Z., T.M. and Z.L. synthesized the small-molecule acceptors or building blocks. J.-L.B., T.W., X.C. and H.L. performed the MD simulations. L.Y. and H.A. wrote the manuscript. All authors contributed to editing the manuscript. H.A., J.-L.B. and H.Y. supervised the projects.

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Correspondence to He Yan or Harald Ade.

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Ye, L., Hu, H., Ghasemi, M. et al. Quantitative relations between interaction parameter, miscibility and function in organic solar cells. Nature Mater 17, 253–260 (2018). https://doi.org/10.1038/s41563-017-0005-1

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