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Polyatomic molecules with emission quantum yields >20% enable efficient organic light-emitting diodes in the NIR(II) window

Nature Photonics volume 16, pages 843–850 (2022)Cite this article

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Abstract

The emission of light by polyatomic molecules in the spectral region of the second near-infrared (NIR(II)) window is severely hampered by the energy gap law, namely the quenching induced by exciton–vibration coupling. As a result, organic light-emitting diodes (OLEDs) with efficient emission wavelengths of ~1,000 nm and above are rare, despite their potential for phototherapy and bioimaging. In this study we revisit the theory of the energy gap law to quantify the contribution of each coupled vibrational mode to non-radiative transitions. The results lead us to propose two approaches that favour emission: molecular packing to extend exciton delocalization, and deuterium substitution to reduce high-frequency vibrations. We provide an experimental proof of concept by designing and synthesizing a new series of self-assembled Pt(II) complexes that exhibit high-intensity phosphorescence with peak quantum yields of (23 ± 0.3)% at approximately 1,000 nm. The corresponding OLEDs emit at a peak wavelength of 995 nm with a maximum external quantum efficiency of 4.31% and a radiance of 1.55 W sr−1 m−2, marking a substantial contribution to the development of efficient OLEDs in the NIR(II) region.

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Fig. 1: The computational approach.
Fig. 2: Structures of the representative chelates and associated Pt(II) metal complexes.
Fig. 3: Absorption and emission spectra of the studied Pt(II) complexes.
Fig. 4: GIXD data analyses.
Fig. 5: Device characteristics of the NIR OLEDs using the studied Pt(II) complexes as the EML.

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Data availability

The data that support the plots and other findings within this paper are available from the corresponding author upon reasonable request.

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Acknowledgements

We are grateful to the National Center for High-performance Computing (NCHC) of Taiwan for the valuable computer time and facilities. We acknowledge the National Synchrotron Radiation Research Center (NSRRC) of Taiwan for the use of their facilities. Y.C. thanks the Innovation and Technology Fund (ITS/196/20) and the NSFC-RGC Joint Research Scheme (N_CityU102/19) of Hong Kong for the generous financial support. P.-T.C. thanks the Ministry of Science and Technology of Taiwan (grant no. MOST-110-2639-M-002-001-ASP) for support. L.-S.L. acknowledges financial support from the Natural Science Foundation of China (no. 61961160731) and the Collaborative Innovation Center of Suzhou Nano Science and Technology.

Author information

Author notes

  1. These authors contributed equally: Sheng-Fu Wang, Bo-Kang Su, Xue-Qi Wang.

Authors and Affiliations

  1. National Tsing Hua University, Department of Chemistry and Frontier Research Center on Fundamental and Applied Sciences of Matters, Hsinchu, Taiwan

    Sheng-Fu Wang, Li-Wen Fu & Yun Chi

  2. National Taiwan University, Department of Chemistry, Taipei, Taiwan

    Bo-Kang Su, Yu-Chen Wei, Kai-Hua Kuo, Chih-Hsing Wang, Shih-Hung Liu & Pi-Tai Chou

  3. Soochow University, Institute of Functional Nano and Soft Materials (FUNSOM), Soochow, China

    Xue-Qi Wang & Liang-Sheng Liao

  4. National Taiwan Ocean University, Institute of Optoelectronic Sciences, Keelung, Taiwan

    Wen-Yi Hung

  5. National Synchrotron Radiation Research Center, Hsinchu, Taiwan

    Wei-Tsung Chuang

  6. The Chinese University of Hong Kong, Department of Physics, Hong Kong, China

    Minchao Qin & Xinhui Lu

  7. City University of Hong Kong, Department of Materials Science and Engineering, Department of Chemistry, and Center of Super-Diamond and Advanced Films (COSDAF), Hong Kong, China

    Caifa You & Yun Chi

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Contributions

S.-F.W., L.-W.F., C.Y. and Y.C. designed and executed the synthesis of all Pt(II) complexes. B.-K.S., Y.-C.W., K.-H.K., C.-H.W. and S.-H.L. conducted optical measurements and theoretical derivations. X.-Q.W., L.-S.L. and W.-Y.H. executed OLED fabrications and analysed the data. P.-T.C. developed the theoretical approach and drafted the manuscript. W.-T.C., M.Q. and X.L. performed the GIXD experiments and conducted the data analysis. All authors discussed the results and contributed to the paper.

Corresponding authors

Correspondence to Liang-Sheng Liao, Wen-Yi Hung, Yun Chi or Pi-Tai Chou.

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Supplementary discussion, Schemes 1–7, Figs. 1–34 and Tables 1–4.

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Wang, SF., Su, BK., Wang, XQ. et al. Polyatomic molecules with emission quantum yields >20% enable efficient organic light-emitting diodes in the NIR(II) window. Nat. Photon. 16, 843–850 (2022). https://doi.org/10.1038/s41566-022-01079-8

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