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Efficient solid-state photon upconversion enabled by triplet formation at an organic semiconductor interface

Nature Photonics volume 15, pages 895–900 (2021)Cite this article

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Abstract

The energy of photons, that is, the wavelength of light, can be upgraded through interactions with materials in a process called photon upconversion1. Although upconversion in organic solids is important for various applications, such as photovoltaics and bioimaging, conventional upconversion systems, based on intersystem crossing (ISC), suffer from low efficiency2,3,4,5,6. Here we report a novel upconversion system with heterojunctions of organic semiconductors. The upconversion occurs through charge separation and recombination, which mediate charge transfer states at the interface. This process can efficiently convert the incident photons to triplets without relying on ISC, which is typically facilitated by the heavy-atom effect1. As a result, a solid-state upconversion system is achieved with an external efficiency that is two orders of magnitude higher than those demonstrated by conventional systems6. Using this result, efficient upconversion, from near-infrared to visible light, can be realized on flexible organic thin films under a weak light-emitting-diode-induced excitation, observable by naked eyes.

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Fig. 1: UC mechanism at an organic semiconductor interface.
Fig. 2: UC emission at the D/A interface.
Fig. 3: Optical investigations of UC emission.
Fig. 4: Investigations of the UC mechanism.

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Data availability

The main data supporting the findings of this study are available within the article and its Supplementary Information. Extra data are available from the corresponding authors on reasonable request.

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Acknowledgements

This research was supported in part by JSPS KAKENHI, Grant-in-Aid for Young Scientists no. 18K14115 (S.I.), the Mazda Foundation (S.I.), the Kao Foundation for Arts and Sciences (S.I.) and Konica Minolta Science and Technology Foundation (S.I.). We thank T. Ueda from the Instrument Center in the Institute for Molecular Science for his assistance with most of the optical measurements. We thank K. Tajima and K. Nakano (RIKEN) for assistance with the highly sensitive EQE measurements of photovoltaic devices. We also thank K. Tajima (RIKEN) and M. Takahashi (Shizuoka University) for their valuable comments.

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Authors and Affiliations

  1. Institute for Molecular Science, Okazaki, Aichi, Japan

    Seiichiro Izawa & Masahiro Hiramoto

  2. The Graduate University for Advanced Studies (SOKENDAI), Okazaki, Aichi, Japan

    Seiichiro Izawa & Masahiro Hiramoto

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  1. Seiichiro Izawa
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S.I. directed the project, conceived the idea, designed and performed the experiments and wrote the paper. M.H. supervised the research. Both authors reviewed the manuscript.

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Correspondence to Seiichiro Izawa.

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Peer review information Nature Photonics thanks the anonymous reviewers for their contribution to the peer review of this work.

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Supplementary Information

Materials and Methods, Supplementary Figs. 1–7, Tables 1 and 2 and Discussion.

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Izawa, S., Hiramoto, M. Efficient solid-state photon upconversion enabled by triplet formation at an organic semiconductor interface. Nat. Photon. 15, 895–900 (2021). https://doi.org/10.1038/s41566-021-00904-w

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