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Visualizing excitations at buried heterojunctions in organic semiconductor blends

Nature Materials volume 16, pages 551–557 (2017)Cite this article

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Abstract

Interfaces play a crucial role in semiconductor devices, but in many device architectures they are nanostructured, disordered and buried away from the surface of the sample. Conventional optical, X-ray and photoelectron probes often fail to provide interface-specific information in such systems. Here we develop an all-optical time-resolved method to probe the local energetic landscape and electronic dynamics at such interfaces, based on the Stark effect caused by electron–hole pairs photo-generated across the interface. Using this method, we found that the electronically active sites at the polymer/fullerene interfaces in model bulk-heterojunction blends fall within the low-energy tail of the absorption spectrum. This suggests that these sites are highly ordered compared with the bulk of the polymer film, leading to large wavefunction delocalization and low site energies. We also detected a 100 fs migration of holes from higher- to lower-energy sites, consistent with these charges moving ballistically into more ordered polymer regions. This ultrafast charge motion may be key to separating electron–hole pairs into free charges against the Coulomb interaction.

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Figure 1: Origin of the electroabsorption signal in pump–probe and pump–push–probe measurements.
Figure 2: Pump–push–probe data for PCDTBT/mono-PCBM (4:1) with 500 nm pump and 2,000 nm push pulses arriving after 4.9 ps delay.
Figure 3: Pump–push–probe measurements and resulting EA spectra on PCDTBT/mPCBM 4:1 (black) and 1:4 (red) blends.
Figure 4: Spectral signatures of charges moving through different material regions after the initial charge transfer step.

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References

  1. Agostini, G. & Lamberti, C. Characterization of Semiconductor Heterostructures and Nanostructures 2nd edn (Elsevier, 2013).

    Google Scholar 

  2. Geiger, F. M. Second harmonic generation, sum frequency generation, and χ(3): dissecting environmental interfaces with a nonlinear optical Swiss army knife. Annu. Rev. Phys. Chem. 60, 61–83 (2009).

    Article  CAS  Google Scholar 

  3. Tang, C. W. Two-layer organic photovoltaic cell. Appl. Phys. Lett. 48, 183–185 (1986).

    Article  CAS  Google Scholar 

  4. Halls, J. J. M. et al. Efficient photodiodes from interpenetrating polymer networks. Nature 376, 498–500 (1995).

    Article  CAS  Google Scholar 

  5. Yu, G. & Heeger, A. J. Charge separation and photovoltaic conversion in polymer composites with internal donor/acceptor heterojunctions. J. Appl. Phys. 78, 4510–4515 (1995).

    Article  CAS  Google Scholar 

  6. He, X. et al. Formation of nanopatterned polymer blends in photovoltaic devices. Nano Lett. 10, 1302–1307 (2010).

    Article  CAS  Google Scholar 

  7. He, X. et al. Formation of well-ordered heterojunctions in Polymer:PCBM photovoltaic devices. Adv. Funct. Mater. 21, 139–146 (2011).

    Article  CAS  Google Scholar 

  8. Pfadler, T. et al. Influence of interfacial area on exciton separation and polaron recombination in nanostructured bilayer all-polymer solar cells. ACS Nano 8, 12397–12409 (2014).

    Article  CAS  Google Scholar 

  9. Bakulin, A. A. et al. The role of driving energy and delocalized states for charge separation in organic semiconductors. Science 335, 1340–1344 (2012).

    Article  CAS  Google Scholar 

  10. Rao, A. et al. The role of spin in the kinetic control of recombination in organic photovoltaics. Nature 500, 435–439 (2013).

    Article  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

  13. 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).

    Article  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

  15. Banerji, N., Cowan, S., Leclerc, M., Vauthey, E. & Heeger, A. J. Exciton formation, relaxation, and decay in PCDTBT. J. Am. Chem. Soc. 132, 17459–17470 (2010).

    Article  CAS  Google Scholar 

  16. Etzold, F. et al. Ultrafast exciton dissociation followed by nongeminate charge recombination in PCDTBT:PCBM photovoltaic blends. J. Am. Chem. Soc. 133, 9469–9479 (2011).

    Article  CAS  Google Scholar 

  17. Provencher, F. et al. Slow geminate-charge-pair recombination dynamics at polymer:fullerene heterojunctions in efficient organic solar cells. J. Polym. Sci. B 50, 1395–1404 (2012).

    CAS  Google Scholar 

  18. Provencher, F. et al. Direct observation of ultrafast long-range charge separation at polymer–fullerene heterojunctions. Nat. Commun. 5, 4288 (2014).

    Article  CAS  Google Scholar 

  19. Beiley, Z. M. et al. Morphology-dependent trap formation in high performance polymer bulk heterojunction solar cells. Adv. Energy Mater. 1, 954–962 (2011).

    Article  CAS  Google Scholar 

  20. Cates Miller, N. et al. Molecular packing and solar cell performance in blends of polymers with a bisadduct fullerene. Nano Lett. 12, 1566–1570 (2012).

    Article  Google Scholar 

  21. Cates Miller, N. et al. Factors governing intercalation of fullerenes and other small molecules between the side chains of semiconducting polymers used in solar cells. Adv. Energy Mater. 2, 1208–1217 (2012).

    Article  Google Scholar 

  22. Cates, N. C., Gysel, R., Dahl, J. E. P., Sellinger, A. & McGehee, M. D. Effects of intercalation on the hole mobility of amorphous semiconducting polymer blends. Chem. Mater. 22, 3543–3548 (2010).

    Article  CAS  Google Scholar 

  23. Jakowetz, A. C. et al. What controls the rate of ultrafast charge transfer and charge separation efficiency in organic photovoltaic blends. J. Am. Chem. Soc. 138, 11672–11679 (2016).

    Article  CAS  Google Scholar 

  24. Savoie, B. M. et al. Mesoscale molecular network formation in amorphous organic materials. Proc. Natl Acad. Sci. USA 111, 10055–10060 (2014).

    Article  CAS  Google Scholar 

  25. Savoie, B. M., Jackson, N. E., Chen, L. X., Marks, T. J. & Ratner, M. A. Mesoscopic features of charge generation in organic semiconductors. Acc. Chem. Res. 47, 3385–3394 (2014).

    Article  CAS  Google Scholar 

  26. Cabanillas-Gonzalez, J., Grancini, G. & Lanzani, G. Pump–probe spectroscopy in organic semiconductors: monitoring fundamental processes of relevance in optoelectronics. Adv. Mater. 23, 5468–5485 (2011).

    Article  CAS  Google Scholar 

  27. Sebastian, L., Weiser, G. & Bässler, H. Charge transfer transitions in solid tetracene and pentacene studied by electroabsorption. Chem. Phys. 61, 125–135 (1981).

    Article  CAS  Google Scholar 

  28. Yang, Y. et al. Semiconductor interfacial carrier dynamics via photoinduced electric fields. Science 350, 1061–1065 (2015).

    Article  CAS  Google Scholar 

  29. Scarongella, M. et al. A close look at charge generation in polymer:fullerene blends with microstructure control. J. Am. Chem. Soc. 137, 2908–2918 (2015).

    Article  CAS  Google Scholar 

  30. De Jonghe-Risse, J. et al. Using the Stark effect to understand charge generation in organic solar cells. in Proc. SPIE Vol. 9549 (eds Hayes, S. C. & Bittner, E. R.) 95490J (2015).

    Google Scholar 

  31. Tsutsumi, J., Yamada, T. & Hasegawa, T. Electroabsorption study of charge-transfer excited state in donor-acceptor-type polymer. Trans. Mater. Res. Soc. Jpn 39, 217–219 (2014).

    Article  CAS  Google Scholar 

  32. Sadhanala, A. et al. Preparation of single-phase films of CH3NH3 Pb(I1−xBrx)3 with sharp optical band edges. J. Phys. Chem. Lett. 5, 2501–2505 (2014).

    Article  CAS  Google Scholar 

  33. Melzer, C., Koop, E. J., Mihailetchi, V. D. & Blom, P. W. M. Hole transport in poly(phenylene vinylene)/methanofullerene bulk-heterojunction solar cells. Adv. Funct. Mater. 14, 865–870 (2004).

    Article  CAS  Google Scholar 

  34. Tuladhar, S. M. et al. Ambipolar charge transport in films of methanofullerene and poly(phenylenevinylene)/methanofullerene blends. Adv. Funct. Mater. 15, 1171–1182 (2005).

    Article  CAS  Google Scholar 

  35. Mayer, A. C. et al. Bimolecular crystals of fullerenes in conjugated polymers and the implications of molecular mixing for solar cells. Adv. Funct. Mater. 19, 1173–1179 (2009).

    Article  CAS  Google Scholar 

  36. Greiner, M. T. & Lu, Z.-H. Thin-film metal oxides in organic semiconductor devices: their electronic structures, work functions and interfaces. NPG Asia Mater. 5, e55 (2013).

    Article  CAS  Google Scholar 

  37. Stranks, S. D. & Snaith, H. J. Metal-halide perovskites for photovoltaic and light-emitting devices. Nat. Nano 10, 391–402 (2015).

    Article  CAS  Google Scholar 

  38. Morgenstern, F. S. F. et al. Ultrafast charge- and energy-transfer dynamics in conjugated polymer: cadmium selenide nanocrystal blends. ACS Nano 8, 1647–1654 (2014).

    Article  CAS  Google Scholar 

  39. Böhm, M. L. et al. The influence of nanocrystal aggregates on photovoltaic performance in nanocrystal-polymer bulk heterojunction solar cells. Adv. Energy Mater. 4, 1400139 (2014).

    Article  Google Scholar 

  40. Carey, G. H. et al. Colloidal quantum dot solar cells. Chem. Rev. 115, 12732–12763 (2015).

    Article  CAS  Google Scholar 

  41. Mueller, C. J., Singh, C. R., Fried, M., Huettner, S. & Thelakkat, M. High bulk electron mobility diketopyrrolopyrrole copolymers with perfluorothiophene. Adv. Funct. Mater. 25, 2725–2736 (2015).

    Article  CAS  Google Scholar 

  42. Price, M. B. et al. Hot-carrier cooling and photoinduced refractive index changes in organic–inorganic lead halide perovskites. Nat. Commun. 6, 8420 (2015).

    Article  CAS  Google Scholar 

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Acknowledgements

We would like to thank S. Gélinas, N. Paul and F. Deschler for fruitful discussions. This work was supported by the Engineering and Physical Sciences Research Council (EPSRC) and the Winton Programme for the Physics of Sustainability. A.C.J. thanks the University of Cambridge for funding (CHESS). Synchrotron measurements were undertaken on the SAXS beamline at the Australian Synchrotron, Victoria, Australia and we acknowledge the help of N. Lal with the measurements. S.H. thanks the framework project Soltech for funding.

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  1. Department of Physics, Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, UK

    Andreas C. Jakowetz, Marcus L. Böhm, Aditya Sadhanala, Akshay Rao & Richard H. Friend

  2. Fakultät für Biologie, Chemie und Geowissenschaften, University Bayreuth, Universitätsstrasse 30, 95440 Bayreuth, Germany

    Sven Huettner

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Contributions

A.C.J. performed the pump–push–probe measurements; M.L.B. and S.H. performed the SAXS/WAXS experiments; A.S. conducted the PDS measurement. A.C.J., M.L.B., A.S. and S.H. analysed the data. A.R. and R.H.F. supervised the work. A.C.J., A.R. and R.H.F. wrote the manuscript. All authors commented on the manuscript.

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Correspondence to Akshay Rao or Richard H. Friend.

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Jakowetz, A., Böhm, M., Sadhanala, A. et al. Visualizing excitations at buried heterojunctions in organic semiconductor blends. Nature Mater 16, 551–557 (2017). https://doi.org/10.1038/nmat4865

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