Review Article

Harnessing singlet exciton fission to break the Shockley–Queisser limit

  • Nature Reviews Materials 2, Article number: 17063 (2017)
  • doi:10.1038/natrevmats.2017.63
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Abstract

Singlet exciton fission is a carrier multiplication process in organic semiconductors that generates two electron–hole pairs for each photon absorbed. Singlet fission occurs on sub-100 fs timescales with yields of up to 200%, and photovoltaic devices based on singlet fission have achieved external quantum efficiencies above 100%. The major challenge for the field is to use singlet fission to improve the efficiency of conventional inorganic solar cells, such as silicon, and to break the Shockley–Queisser limit on the efficiency of single-junction photovoltaics. Achieving this goal requires a broader and more collaborative effort than the one used at present. Synthetic chemists, spectroscopists, theorists, materials scientists, device physicists and engineers will need to work together. In this Review, we critically assess the current status of the field, highlight the key results and identify the challenges ahead. In doing so, we seek to open the field to new expertise and ideas, which will in turn promote both fundamental science and device applications.

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References

  1. 1.

    International Energy Agency Technology Roadmap Solar Photovoltaic Energy. IEA (2014).

  2. 2.

    Research opportunities to advance solar energy utilization. Science 351, aad1920 (2016).

  3. 3.

    & Detailed balance limit of efficiency of p-n junction solar cells. J. Appl. Phys. 32, 510–519 (1961).

  4. 4.

    A review of ultrahigh efficiency III-V semiconductor compound solar cells: multijunction tandem, lower dimensional, photonic up/down conversion and plasmonic nanometallic structures. Energies 2, 504–530 (2009).

  5. 5.

    & Photonic design principles for ultrahigh-efficiency photovoltaics. Nat. Mater. 11, 174–177 (2012).

  6. 6.

    et al. Spectroscopic and device aspects of nanocrystal quantum dots. Chem. Rev. 116, 10513–10622 (2016).

  7. 7.

    , & Multiple exciton generation in a quantum dot solar cell. SPIE Newsroom doi: (2012).

  8. 8.

    , , & Third generation photovoltaics based on multiple exciton generation in quantum confined semiconductors. Acc. Chem. Res. 46, 1252–1260 (2013).

  9. 9.

    & Singlet fission. Chem. Rev. 110, 6891–6936 (2010). A comprehensive review of the history of SF, molecules showing SF and possible design rules.

  10. 10.

    et al. Ultrafast dynamics of exciton fission in polycrystalline pentacene. J. Am. Chem. Soc. 133, 11830–11833 (2011). This study demonstrates that SF can occur on sub-100 fs timescales.

  11. 11.

    et al. A transferable model for singlet-fission kinetics. Nat. Chem. 6, 492–497 (2014).

  12. 12.

    , , , & Photophysics of pentacene thin films: the role of exciton fission and heating effects. Phys. Rev. B 84, 195411 (2011).

  13. 13.

    & Effects of magnetic fields on the mutual annihilation of triplet excitons in anthracene crystals. Phys. Rev. B 1, 896–902 (1970).

  14. 14.

    et al. Singlet exciton fission photovoltaics. Acc. Chem. Res. 46, 1300–1311 (2013).

  15. 15.

    , , , & Singlet exciton fission-sensitized infrared quantum dot solar cells. Nano Lett. 12, 1053–1057 (2012).

  16. 16.

    et al. In situ measurement of exciton energy in hybrid singlet-fission solar cells. Nat. Commun. 3, 1019 (2012).

  17. 17.

    et al. External quantum efficiency above 100% in a singlet-exciton-fission–based organic photovoltaic cell. Science 340, 334–337 (2013). This study presents the first demonstration of an SF-enhanced PV device with an EQE above 100%.

  18. 18.

    , , & Singlet exciton fission in solution. Nat. Chem. 5, 1019–1024 (2013).

  19. 19.

    et al. Exciton correlations in intramolecular singlet fission. J. Am. Chem. Soc. 138, 7289–7297 (2016).

  20. 20.

    et al. Intramolecular singlet fission in oligoacene heterodimers. Angew. Chem. Int. Ed. Engl. 55, 3373–3377 (2016).

  21. 21.

    & Triplet states in organic semiconductors. Mater. Sci. Eng. R 66, 71–109 (2009).

  22. 22.

    et al. Ultrafast triplet formation in thionated perylene diimides. J. Phys. Chem. C 118, 9996–10004 (2014).

  23. 23.

    & Quantum beats in crystalline tetracene delayed fluorescence due to triplet pair coherences produced by direct singlet fission. J. Am. Chem. Soc. 134, 8597–8607 (2012). This study provides a demonstration of quantum beating in the photoluminescence of tetracene.

  24. 24.

    et al. Magnetic dipolar interaction between correlated triplets created by singlet fission in tetracene crystals. Nat. Commun. 6, 8602 (2015).

  25. 25.

    et al. Strongly exchange-coupled triplet pairs in an organic semiconductor. Nat. Phys. 13, 176–181 (2016).

  26. 26.

    et al. Quintet multiexciton dynamics in singlet fission. Nat. Phys. 13, 182–188 (2016).

  27. 27.

    , & Magnetic field effects and the role of spin states in singlet fission. Chem. Phys. Lett. 585, 1–10 (2013). A review of magnetic field effects in SF.

  28. 28.

    et al. Geminate and nongeminate recombination of triplet excitons formed by singlet fission. Phys. Rev. Lett. 112, 238701 (2014).

  29. 29.

    et al. Spin signatures of exchange-coupled triplet pairs formed by singlet fission. Phys. Rev. B 94, 045204 (2016).

  30. 30.

    & The dynamics of singlet fission in crystalline tetracene and covalent analogs. Acc. Chem. Res. 46, 1312–1320 (2013).

  31. 31.

    , & The exciton dynamics in tetracene thin films. Phys. Chem. Chem. Phys. 15, 14797–14805 (2013).

  32. 32.

    et al. Identification of a triplet pair intermediate in singlet exciton fission in solution. Proc. Natl Acad. Sci. USA 112, 7656–7661 (2015).

  33. 33.

    et al. Singlet fission in a covalently linked cofacial alkynyltetracene dimer. J. Am. Chem. Soc. 138, 617–627 (2016).

  34. 34.

    et al. Tuning the role of charge-transfer states in intramolecular singlet exciton fission through side-group engineering. Nat. Commun. 7, 13622 (2016).

  35. 35.

    et al. Tuneable singlet exciton fission and triplet–triplet annihilation in an orthogonal pentacene dimer. Adv. Funct. Mater. 25, 5452–5461 (2015).

  36. 36.

    et al. Vibronically coherent ultrafast triplet-pair formation and subsequent thermally activated dissociation control efficient endothermic singlet fission. Nat. Chem. (2017).

  37. 37.

    & High-yield singlet fission in a zeaxanthin aggregate observed by picosecond resonance Raman spectroscopy. J. Am. Chem. Soc. 132, 13988–13991 (2010).

  38. 38.

    et al. Evidence for conical intersection dynamics mediating ultrafast singlet exciton fission. Nat. Phys. 13, 182–188 (2015). This study provides evidence for strong vibronic coupling dynamics mediating SF.

  39. 39.

    , & The energy barrier in singlet fission can be overcome through coherent coupling and entropic gain. Nat. Chem. 4, 840–845 (2012).

  40. 40.

    et al. Observing the multiexciton state in singlet fission and ensuing ultrafast multielectron transfer. Science 334, 1541–1545 (2011). This study presents the observation of ultrafast TT formation with time-resolved photoelectron spectroscopy.

  41. 41.

    et al. Real-time observation of multiexcitonic states in ultrafast singlet fission using coherent 2D electronic spectroscopy. Nat. Chem. 8, 16–23 (2016).

  42. 42.

    & Recent advances in singlet fission. Annu. Rev. Phys. Chem. 64, 361–386 (2013). Another noteworthy review on SF.

  43. 43.

    et al. The quantum coherent mechanism for singlet fission: experiment and theory. Acc. Chem. Res. 46, 1321–1329 (2013).

  44. 44.

    , & The role of chromophore coupling in singlet fission. Acc. Chem. Res. 46, 1290–1299 (2013).

  45. 45.

    , , & Singlet exciton fission in polycrystalline pentacene: from photophysics toward devices. Acc. Chem. Res. 46, 1330–1338 (2013).

  46. 46.

    , & A correlated electron view of singlet fission. Acc. Chem. Res. 46, 1339–1347 (2013).

  47. 47.

    & Charge transfer-mediated singlet fission. Annu. Rev. Phys. Chem. 66, 601–618 (2015).

  48. 48.

    , & in Photochemistry 43, 270–285 (The Royal Society of Chemistry, 2016).

  49. 49.

    , , , & Charge-transfer excitations steer the Davydov splitting and mediate singlet exciton fission in pentacene. Phys. Rev. Lett. 110, 226402 (2013).

  50. 50.

    et al. Enabling singlet fission by controlling intramolecular charge transfer in π-stacked covalent terrylenediimide dimers. Nat. Chem. 8, 1120–1125 (2016).

  51. 51.

    , , & Lessons from nature about solar light harvesting. Nat. Chem. 3, 763–774 (2011).

  52. 52.

    et al. Coherent ultrafast charge transfer in an organic photovoltaic blend. Science 344, 1001–1005 (2014).

  53. 53.

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

  54. 54.

    et al. A direct mechanism of ultrafast intramolecular singlet fission in pentacene dimers. ACS Cent. Sci. 2, 316–324 (2016).

  55. 55.

    & Intermolecular vibrational modes speed up singlet fission in perylenediimide crystals. J. Phys. Chem. Lett. 6, 360–365 (2015).

  56. 56.

    , , & Mechanism for singlet fission in pentacene and tetracene: from single exciton to two triplets. J. Am. Chem. Soc. 133, 19944–19952 (2011).

  57. 57.

    , , & Functional mode singlet fission theory. J. Phys. Chem. C 121, 4130–4138 (2017).

  58. 58.

    & Vibronic exciton theory of singlet fission. II. Two-dimensional spectroscopic detection of the correlated triplet pair state. J. Chem. Phys. 146, 174704 (2017).

  59. 59.

    et al. Temperature-independent singlet exciton fission in tetracene. J. Am. Chem. Soc. 135, 16680–16688 (2013).

  60. 60.

    , , , & Polymorphism influences singlet fission rates in tetracene thin films. Chem. Sci. 7, 1185–1191 (2015).

  61. 61.

    & How morphology affects singlet fission in crystalline tetracene. J. Phys. Chem. Lett. 6, 1841–1846 (2015).

  62. 62.

    et al. Singlet fission in pentacene dimers. Proc. Natl Acad. Sci. USA 112, 5325–5330 (2015).

  63. 63.

    , & Slow singlet fission observed in a polycrystalline perylenediimide thin film. J. Phys. Chem. Lett. 7, 4922–4928 (2016).

  64. 64.

    et al. Singlet exciton fission in polycrystalline thin films of a slip-stacked perylenediimide. J. Am. Chem. Soc. 135, 14701–14712 (2013).

  65. 65.

    et al. Singlet exciton fission in thin films of tert-butyl-substituted terrylenes. J. Phys. Chem. A 119, 4151–4161 (2015).

  66. 66.

    et al. A design strategy for intramolecular singlet fission mediated by charge-transfer states in donor–acceptor organic materials. Nat. Mater. 14, 426–433 (2015).

  67. 67.

    et al. Recent advances in bulk heterojunction polymer solar cells. Chem. Rev. 115, 12666–12731 (2015).

  68. 68.

    & Triplet transport in thin films: fundamentals and applications. Chem. Commun. 53, 4429–4440 (2017).

  69. 69.

    , , & White organic light-emitting diodes: status and perspective. Rev. Mod. Phys. 85, 1245–1293 (2013).

  70. 70.

    , , , & Long-term stable organic photodetectors with ultra low dark currents for high detectivity applications. Sci. Rep. 6, 39201 (2016).

  71. 71.

    Two ideas on energy transfer phenomena: ion-pair effects involving the OH stretching mode, and sensitization of photovoltaic cells. J. Lumin. 18, 779–784 (1979). This study presents seminal work showing how to use SF to enhance the efficiency of silicon solar cells.

  72. 72.

    & Updated assessment of possibilities and limits for solar cells. Adv. Mater. 26, 1622–1628 (2014).

  73. 73.

    et al. Fullerene-free polymer solar cells with over 11% efficiency and excellent thermal stability. Adv. Mater. 28, 4734–4739 (2016).

  74. 74.

    et al. Fast charge separation in a non-fullerene organic solar cell with a small driving force. Nat. Energy 1, 16089 (2016).

  75. 75.

    , , & Beyond Langevin recombination: how equilibrium between free carriers and charge transfer states determines the open-circuit voltage of organic solar cells. Adv. Energy Mater. 5, 1500123 (2015).

  76. 76.

    , & High efficiency organic multilayer photodetectors based on singlet exciton fission. Appl. Phys. Lett. 95, 033301 (2009).

  77. 77.

    et al. Triplet exciton dissociation in singlet exciton fission photovoltaics. Adv. Mater. 24, 6169–6174 (2012).

  78. 78.

    , , , & Slow light enhanced singlet exciton fission solar cells with a 126% yield of electrons per photon. Appl. Phys. Lett. 103, 263302 (2013).

  79. 79.

    , & Highly efficient organic tandem solar cells: a follow up review. Energy Environ. Sci. 6, 2390–2413 (2013).

  80. 80.

    & A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films. Nature 353, 737–740 (1991).

  81. 81.

    et al. Status and outlook of sensitizers/dyes used in dye sensitized solar cells (DSSC): a review. Int. J. Energy Res. 40, 1303–1320 (2016).

  82. 82.

    , , , & Hybrid pentacene/a-silicon solar cells utilizing multiple carrier generation via singlet exciton fission. Appl. Phys. Lett. 101, 153507 (2012).

  83. 83.

    et al. Solution-processable singlet fission photovoltaic devices. Nano Lett. 15, 354–358 (2015).

  84. 84.

    National Renewable Energy Laboratory. PV efficiency chart. NREL (2017).

  85. 85.

    et al. Resonant energy transfer of triplet excitons from pentacene to PbSe nanocrystals. Nat. Mater. 13, 1033–1038 (2014). This study demonstrates efficient triplet transfer from pentacene to PbSe nanoparticles.

  86. 86.

    et al. Energy harvesting of non-emissive triplet excitons in tetracene by emissive PbS nanocrystals. Nat. Mater. 13, 1039–1043 (2014). This study demonstrates efficient triplet transfer from tetracene to PbS nanoparticles.

  87. 87.

    et al. Hybrid molecule–nanocrystal photon upconversion across the visible and near-infrared. Nano Lett. 15, 5552–5557 (2015).

  88. 88.

    , , , & Triplet energy transfer from PbS(Se) nanocrystals to rubrene: the relationship between the upconversion quantum yield and size. Adv. Func. Mater. 26, 6091–6097 (2016).

  89. 89.

    , , , & Direct observation of triplet energy transfer from semiconductor nanocrystals. Science 351, 369–372 (2016).

  90. 90.

    et al. Solid-state infrared-to-visible upconversion sensitized by colloidal nanocrystals. Nat. Photon. 10, 31–34 (2015).

  91. 91.

    et al. Dynamics of molecular excitons near a semiconductor surface studied by fluorescence quenching of polycrystalline tetracene on silicon. Chem. Phys. Lett. 601, 33–38 (2014).

  92. 92.

    et al. Nanocrystal shape and the mechanism of exciton spin relaxation. Nano Lett. 6, 1765–1771 (2006).

  93. 93.

    et al. Predicting the outdoor performance of flat-plate III–V/Si tandem solar cells. Solar Energy 149, 77–84 (2017).

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Acknowledgements

A.R. and R.H.F. thank M. Taybjee and J. Allardice for help with preparing Fig. 3b,c. A.R. and R.H.F. thank the Engineering and Physical Sciences Research Council (EPSRC) and the Winton Programme for the Physics of Sustainability for funding.

Author information

Affiliations

  1. Cavendish Laboratory, J.J. Thomson Avenue, University of Cambridge, Cambridge CB3 OHE, UK.

    • Akshay Rao
    •  & Richard H. Friend

Authors

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Contributions

A.R. obtained the data for the article. Both authors made substantial contributions to the content, wrote the manuscript and reviewed and/or edited the manuscript before submission.

Competing interests

The authors declare no competing interests.

Corresponding author

Correspondence to Akshay Rao.