Organic light-emitting transistors with an efficiency that outperforms the equivalent light-emitting diodes

Journal name:
Nature Materials
Volume:
9,
Pages:
496–503
Year published:
DOI:
doi:10.1038/nmat2751
Received
Accepted
Published online

Abstract

The potential of organic semiconductor-based devices for light generation is demonstrated by the commercialization of display technologies based on organic light-emitting diodes (OLEDs). Nonetheless, exciton quenching and photon loss processes still limit OLED efficiency and brightness. Organic light-emitting transistors (OLETs) are alternative light sources combining, in the same architecture, the switching mechanism of a thin-film transistor and an electroluminescent device. Thus, OLETs could open a new era in organic optoelectronics and serve as testbeds to address general fundamental optoelectronic and photonic issues. Here, we introduce the concept of using a p-channel/emitter/n-channel trilayer semiconducting heterostructure in OLETs, providing a new approach to markedly improve OLET performance and address these open questions. In this architecture, exciton–charge annihilation and electrode photon losses are prevented. Our devices are >100 times more efficient than the equivalent OLED, >2× more efficient than the optimized OLED with the same emitting layer and >10 times more efficient than any other reported OLETs.

At a glance

Figures

  1. Trilayer OLET device structure and active materials forming the heterostructure.
    Figure 1: Trilayer OLET device structure and active materials forming the heterostructure.

    a, Schematic representation of the trilayer OLET device with the chemical structure of each material making up the device active region. The field-effect charge transport and the light-generation processes are also sketched. b, Energy-level diagram of the trilayer heterostructure. The energy values of the HOMO and LUMO levels of each molecular material are indicated together with the Fermi level of the gold contacts.

  2. Optical micrographs of the lit trilayer OLET and its emission spectra.
    Figure 2: Optical micrographs of the lit trilayer OLET and its emission spectra.

    a, Optical micrograph of the interdigitated trilayer heterostructure OLET biased with VDS=VGS=90 V. Channel length and channel width are 150 μm and 20 cm, respectively. b, Optical micrograph of the OLET channel when no bias is applied to the device, and when the applied bias is VDS=VGS=90 V. The schematic representation of the trilayer heterostructure OLET showing the expected location of the light-generation area is reported in the inset. c, Comparison between the electroluminescence (EL) and photoluminescence (PL) spectra of the trilayer heterostructure OLET.

  3. Optoelectronic characteristics of the trilayer OLET and topographical images of the individual layers forming the heterostructure.
    Figure 3: Optoelectronic characteristics of the trilayer OLET and topographical images of the individual layers forming the heterostructure.

    a,b, Locus electrical curves of the OLET in n-polarization (a) and in p-polarization (b). During the n-polarization the electroluminescence output power (magenta) is also collected. c, In the transfer characteristic curves, the source–drain current (IDS) is measured keeping the drain–source potential constant at 90 V, while sweeping the gate-source potential from 0 to 90 V. d, AFM image of a 7-nm-thick DFH-4T film grown on glass/ITO/PMMA substrate. e, AFM image of a 40-nm-thick film of Alq3:(3%)DCM blend grown on top of the DFH-4T thin film reported in d. f, AFM image of a 15-nm-thick DH-4T film grown on top of the Alq3:(3%)DCM film reported in e. For ease of comparison the same z-axis colour scale is used for both images e and f.

  4. Images of the light-emitting area within the OLET device channel.
    Figure 4: Images of the light-emitting area within the OLET device channel.

    a, For reference, an optical micrograph of the device channel without bias, to highlight the position of the drain electrode edge that is marked with a yellow line. bd, Optical micrographs of the emission zone within the device channel of the trilayer heterostructure OLET during a transfer scan at VDS=90 V and VGS values of 30 V (b), 60 V (c) and 90 V (d). Three arrows in bd indicate the initial position of the recombination and emission zone.

  5. EQE as a function of the applied gate voltage for the two trilayer heterostructure OLET configurations.
    Figure 5: EQE as a function of the applied gate voltage for the two trilayer heterostructure OLET configurations.

    a, The bottom layer and the top layer are thin films of DHF-4T and DH-4T, respectively. b, The layer configuration of a is reversed. The transfer curves with the drain–source current (IDS) plotted on a logarithmic scale are also reported. IDS is measured keeping the drain-source potential constant at 90 V, while sweeping the gate-source potential from 0 to 90 V.

  6. Device structure and optoelectronic characteristics of the trilayer OLED in direct and reverse configurations.
    Figure 6: Device structure and optoelectronic characteristics of the trilayer OLED in direct and reverse configurations.

    a, Schematic structure of the trilayer OLED in the direct configuration. b, Optoelectronic characteristics of the OLED sketched in a. c, EQE of the direct heterostructure OLED. d, Schematic structure of the trilayer OLED in the reverse configuration. e, Optoelectronic characteristics of the OLED sketched in d. f, EQE of the reverse heterostructure OLED.

References

  1. Yan, H. et al. A high-mobility electron-transporting polymer for printed transistors. Nature 457, 680687 (2009).
  2. Forrest, S. R. The path to ubiquitous and low-cost organic electronic appliances on plastic. Nature 428, 911918 (2004).
  3. Malliaras, G. & Friend, R. H. An organic electronics primer. Phys. Today 58, 5358 (2005).
  4. Park, S. H. et al. Bulk heterojunction solar cells with internal quantum efficiency approaching 100%. Nature Photon. 3, 297303 (2009).
  5. Margapoti, E. et al. Excimer emission in single layer electroluminescent device based on [Ir(4,5-diphenyl-2-methylthiazolo)2(5-methyl-1,10-phenanthroline)]+[PF6] . J. Phys. Chem. C 113, 1251712522 (2009).
  6. Chua, L-L. et al. General observation of n-type field-effect behaviour in organic semiconductors. Nature 434, 194199 (2005).
  7. Muccini, M. A bright future for organic field-effect transistors. Nature Mater. 5, 605613 (2006).
  8. Hepp, A. et al. Light-emitting field-effect transistor based on tatracene thin film. Phys. Rev. Lett. 91, 157406 (2003).
  9. Rost, C. et al. Ambipolar light-emitting organic field-effect transistor. Appl. Phys. Lett. 85, 16131615 (2004).
  10. Takenobu, T. et al. High current density in light-emitting transistors of organic single crystals. Phys. Rev. Lett. 100, 066601 (2008).
  11. Verlaak, S., Cheyns, D., Debucquoy, M., Arkhipov, V. & Heremans, P. Numerical simulation of tetracene light-emitting transistors: A detailed balance of exciton processes. Appl. Phys. Lett. 85, 24052407 (2004).
  12. Gehlhaar, R., Yahiro, M. & Adachi, C. Finite difference time domain analysis of the light extraction efficiency in organic light-emitting field-effect transistors. J. Appl. Phys. 104, 331161331165 (2008).
  13. Santato, C. et al. Tetracene light-emitting transistors on flexible plastic substrates. Appl. Phys. Lett. 86, 14110611411063 (2005).
  14. Cicoria, F. et al. Organic light-emitting transistors based on solution-cast and vacuum-sublimed films of a rigid core thiophene oligomer. Adv. Mater. 18, 169174 (2006).
  15. Capelli, R. et al. Investigation of the opto-electronic properties of organic light emitting transistors based on an intrinsically ambipolar material. J. Phys. Chem. C 112, 1299312999 (2008).
  16. Yuen, M-Y. et al. Semiconducting and electroluminescent nanowires self-assembled from organoplatinum(II) complexes. Angew. Chem. Int. Ed. 47, 98959899 (2008).
  17. Yamamoto, H., Oyamada, T., Sasabe, H. & Adachi, C. Amplified spontaneous emission under optical pumping from an organic semiconductor laser structure equipped with transparent carrier injection electrodes. Appl. Phys. Lett. 84, 14011403 (2004).
  18. Baldo, M. A., Holmes, R. J. & Forrest, S. R. Prospects for electrically pumped organic lasers. Phys. Rev. B 66, 035321 (2002).
  19. List, E. J. W. et al. Interaction of singlet excitons with polarons in wide band-gap organic semiconductors: A quantitative study. Phys. Rev. B 64, 155204 (2001).
  20. Staudigel, J., Stößel, M., Steuber, F. & Simmerer, J. A quantitative numerical model of multilayer vapor-deposited organic emitting diodes. J. Appl. Phys. 86, 38953910 (1999).
  21. Gärtner, C., Karnutsch, C. & Lemmer, U. The influence of annihilation processes on the threshold current density of organic laser diodes. J. Appl. Phys. 101, 231071231079 (2007).
  22. Swensen, J. S., Soci, C. & Heeger, A. J. Light emission from an ambipolar semiconducting polymer field-effect transistor. Appl. Phys. Lett. 87, 253511 (2005).
  23. Zaumseil, J., Friend, R. H. & Sirringhaus, H. Spatial control of the recombination zone in an ambipolar light-emitting organic transistor. Nature Mater. 5, 6974 (2006).
  24. Zaumseil, J., Donley, C. L., Kim, J-S., Friend, R. H. & Sirringhaus, H. Efficient top-gate, ambipolar, light-emitting field-effect transistors based on a green-light-emitting polyfluorene. Adv. Mater. 18, 27082712 (2006).
  25. Bisri, S. Z. et al. High mobility and luminescent efficiency in organic single-crystal light-emitting transistors. Adv. Funct. Mater. 19, 17281735 (2009).
  26. Wang, Y., Kumashiro, R., Nouchi, R., Komatsu, N. & Tanigaki, K. Influence of interface modifications on carrier mobilities in rubrene single crystal ambipolar field-effect transistors. J. Appl. Phys. 105, 124912 (2009).
  27. Schidleja, M., Melzer, C. & Seggern, H. Electroluminescence from a pentacene based ambipolar organic field-effect transistor. Appl. Phys. Lett. 94, 123307 (2009).
  28. Zaumseil, J. et al. Quantum efficiency of ambipolar light-emitting polymer field-effect transistors. J. Appl. Phys 103, 064517 (2008).
  29. Ke, T-H. et al. High efficiency blue light emitting unipolar transistor incorporating multifunctional electrodes. Appl. Phys. Lett. 94, 15330711533073 (2009).
  30. Namdas, E. B. et al. Gate-controlled light emitting diodes. Adv. Mater. 20, 13211324 (2008).
  31. Suganuma, N., Shimoji, N., Oku, Y. & Matsushige, K. Novel organic light-emitting transistors with PN-heteroboundary carrier recombination sites fabricated by lift-off patterning of organic semiconductor thin-films. J. Mater. Res. 22, 29822986 (2007).
  32. Namdas, E. B., Ledochowitsch, P., Yuen, J. D., Moses, D. & Heeger, A. J. High performance light emitting transistors. Appl. Phys. Lett. 92, 183304 (2008).
  33. Dinelli, F. et al. High-mobility ambipolar transport in organic light-emitting transistors. Adv. Mater. 18, 14161420 (2006).
  34. Matsushima, T. & Adachi, C. Extremely low voltage light-emitting diodes with p-doped alpha-sexithiophene hole transport and n-doped phenyldipyrenylphosphine oxide electron transport layers. Appl. Phys. Lett. 89, 253506 (2006).
  35. Facchetti, A. et al. Building blocks for n-type molecular and polymeric electronics. perfluoroalkyl- versus alkyl-functionalized oligothiophenes (nT;n=2–6). Systematics of thin film microstructure, semiconductor performance, and modeling of majority charge injection in field-effect transistors. J. Am. Chem. Soc. 126, 1385913874 (2004).
  36. Garnier, F. et al. Dihexylquaterthiophene, a two-dimensional liquid crystal-like orgnic semiconductor with high transport properties. Chem. Mater. 10, 33343339 (1998).
  37. Schols, S. et al. Organic light-emitting diodes with field-effect-assisted electron transport based on α,ω-diperfluorohexyl-quaterthiophene. Adv. Funct. Mater. 18, 36453652 (2008).
  38. Ackermann, J. et al. Control of growth and charge transport properties of quaterthiophene thin films via hexyl chain substitutions. Org. Electr. 5, 213222 (2004).
  39. Loi, M. A. et al. Supramolecular organization in ultra-thin films of α-sexithiophene on silicon dioxide. Nature Mater. 4, 8185 (2005).
  40. Da Como, E., Loi, M. A., Murgia, M., Zamboni, R. & Muccini, M. J-aggregation in α-sexithiophene submonolayer films on silicon dioxide. J. Am. Chem. Soc. 128, 42774281 (2006).
  41. Yan, H., Kagata, T. & Okuzaki, H. Ambipolar pentacene/C60-based field-effect transistors with high hole and electron mobilities in ambient atmosphere. Appl. Phys. Lett. 94, 023305 (2009).
  42. Ye, R., Baba, M., Ohta, K., Kazunori Suzuki, K. & Mori, K. Fabrication of ambipolar organic heterojunction transistors with various sexithiophene alkyl-substituted derivatives. Jpn. J. Appl. Phys. 48, 04C168 (2009).
  43. Li, J-F., Chang, W-L., Ou, G-P. & Zhang, F-J. Air-stable ambipolar organic field effect transistors with heterojunction of pentacene and N,N′-bis(4-trifluoromethylben-zyl) perylene-3,4,9,10- tetracarboxylic diimide. Chin. Phys. B 18, 30023007 (2009).
  44. Uddin, A., Lee, C. B., Hu, X., Wong, T. K. S. & Sun, X. W. Effect of doping on optical and transport properties of charge carries in Alq3 . J. Cryst. Growth 288, 115118 (2006).
  45. Muck, T. et al. In situ electrical characterization of DH4T field-effect transistors. Synth. Met. 146, 317320 (2004).
  46. DiBenedetto, S. A., Facchetti, A., Rainer, M. A. & Marks, T. J. Molecular self-assembled monolayers and multilayers for organic and unconventional inorganic thin-film transistor applications. Adv. Mater. 21, 14071433 (2009).
  47. Pinto, J. C. et al. Organic thin film transistors with polymer brush gate dielectrics synthesized by atom transfer radical polymerization. Adv. Funct. Mater. 18, 3643 (2008).

Download references

Author information

Affiliations

  1. Consiglio Nazionale delle Ricerche (CNR), Istituto per lo Studio dei Materiali Nanostrutturati (ISMN), via P. Gobetti 101, I-40129 Bologna, Italy

    • Raffaella Capelli,
    • Stefano Toffanin,
    • Gianluca Generali &
    • Michele Muccini
  2. Polyera Corporation, 8045 Lamon Avenue, Skokie, Illinois 60077, USA

    • Hakan Usta &
    • Antonio Facchetti
  3. E.T.C. srl, via P. Gobetti 101, I-40129 Bologna, Italy

    • Michele Muccini

Contributions

R.C. defined the concept of the trilayer heterostructure, fabricated devices, executed optoelectronic experiments, analysed and interpreted results. S.T. defined the concept of the trilayer heterostructure, executed spectroscopic and photonic experiments, analysed and interpreted results. G.G. carried out AFM measurements, contributed to fabricate devices and to execute optoelectronic experiments. H.U. synthesized DH-4T and DFH-4T. A.F. supervised the synthesis and discussed the results. M.M. defined the concept of the trilayer heterostructure, took part to the key experiments, interpreted results and supervised the entire work. A.F. and M.M. wrote the manuscript.

Competing financial interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to:

Author details

Supplementary information

PDF files

  1. Supplementary Information (548 KB)

    Supplementary Information

Additional data