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Next-generation OLEDs: new materials and emission mechanisms

Abstract: The efficiency of organic light-emitting diodes (OLEDs) is fundamentally determined by the spin of excited state electrons. For conventional fluorescent OLEDs [1, 2], the radiative recombination of triplet excitons is spin-forbidden, limiting the maximum internal quantum efficiency of electroluminescence to the generation probability of singlet excitons. In the past decades, high-efficiency phosphorescent [3, 4] and thermally activated delayed fluorescence [5] OLEDs, which utilise triplet excitons effectively, were demonstrated. In our recent work [6], using a new class of emissive molecules, carbene-metal-amides, we present an unusual emission pathway based on rotationally accessed spin-state inversion (RASI), which results in extremely efficient spin-state interconversion and photoemission. To investigate this unique emission mechanism, detailed time-resolved luminescence spectroscopy and quantum chemical calculations have been carried out. The performance metrics of our best solution-processed OLEDs (with peak external quantum efficiencies of 27.5%) are comparable to, or exceeding those of state-of-the-art OLEDs and quantum-dot LEDs. Considerations for the design of molecular materials based on this principle, and new approaches for achieving fully solution-processed multi-layer device architectures will be addressed. Besides, an overview of other relevant research activities in our group, including the investigation of triplet exciton fusion [7] for next generation optoelectronics, will be presented.

[1] C. W. Tang & S. A. VanSlyke, Appl. Phys. Lett. 51, 913 (1987).

[2] J. H. Burroughes, R. H. Friend et al, Nature 347, 539–541 (1990).

[3] Y. Ma et al, Synth. Met. 94, 245-248 (1998).

[4] M. A. Baldo, S. Forrest et al, Nature 395, 151–154 (1998).

[5] H. Uoyama, C. Adachi et al, Nature 492, 234–238 (2012).

[6] D. Di, A. S. Romanov, L. Yang, R. H. Friend, M. Linnolahti, M. Bochmann, D. Credgington et al, “High-performance light-emitting diodes based on carbene-metal-amides”, Science 356, 159-163 (2017).

[7] D. Di, L. Yang, R. H. Friend et al, “Efficient triplet exciton fusion in molecularly-doped polymer light-emitting diodes”, Advanced Materials 29, 1605987 (2017).

BiographyDawei Di (狄大卫) 博士现职为剑桥大学物理系卡文迪许实验室博士后。他先后在澳大利亚新南威尔士大学和英国剑桥大学获得了光伏太阳能工程学学士(一等荣誉学位)、光伏工程学博士和物理学博士学位,师从有机光电物理学权威卡文迪许物理学教授Richard Friend院士(FRS, FREng, FIEE, FInstP, Kt)和太阳能电池权威Martin Green院士(FRS, AM, FIEEE, FAA, FTSE)Di博士的研究工作主要涉及新型有机发光材料中激子自旋态动力学、高性能有机发光二极管(OLED)、钙钛矿LED、纳米硅太阳能电池,以及与上述课题有关的器件物理和光物理。他近期的主要学术贡献是发现了有机发光二极管(OLED)的新型高效发光机制RASI并突破低成本OLED效率纪录,以及对OLED和钙钛矿LED激发态发光的研究。另外,他还推动了硅基层叠太阳能电池的发展,并研制了纳米硅/晶体硅发光二极管。他的工作获得了国际同行的广泛关注。

Dawei Di博士至今共发表SCI期刊论文20篇,申请了4项国际专利,撰写了1个书籍章节,翻译并出版了3部太阳能电池的权威教材。他以第一编辑或通信编辑身份在ScienceAdvanced MaterialsJournal of Physical Chemistry Letters等高影响力期刊共发表论文9篇。Di博士近期的研究进展被Nature MaterialsNature Reviews Chemistry等权威杂志和几十家媒体报道和评论。他还担任 Nano LettersApplied Physics LettersJournal of Physical Chemistry Letters15家国际期刊的审稿人。

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