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. 2024 May 23;15(1):4394.
doi: 10.1038/s41467-024-48659-6.

Stable pure-green organic light-emitting diodes toward Rec.2020 standard

Xun Tang  1 , Tuul Tsagaantsooj  2 , Tharindu P B Rajakaruna  2 , Kai Wang  3 , Xian-Kai Chen  3 , Xiao-Hong Zhang  3 , Takuji Hatakeyama  4 , Chihaya Adachi  5   6
Affiliations

Stable pure-green organic light-emitting diodes toward Rec.2020 standard

Xun Tang et al. Nat Commun. .

Abstract

Manipulating dynamic behaviours of charge carriers and excitons in organic light-emitting diodes (OLEDs) is essential to simultaneously achieve high colour purity and superior operational lifetime. In this work, a comprehensive transient electroluminescence investigation reveals that incorporating a thermally activated delayed fluorescence assistant molecule with a deep lowest unoccupied molecular orbital into a bipolar host matrix effectively traps the injected electrons. Meanwhile, the behaviours of hole injection and transport are still dominantly governed by host molecules. Thus, the recombination zone notably shifts toward the interface between the emissive layer (EML) and the electron-transporting layer (ETL). To mitigate the interfacial carrier accumulation and exciton quenching, this bipolar host matrix could serve as a non-barrier functional spacer between EML/ETL, enabling the distribution of recombination zone away from this interface. Consequently, the optimized OLED exhibits a low driving voltage, promising device stability (95% of the initial luminance of 1000 cd m-2, LT95 > 430 h), and a high Commission Internationale de L'Éclairage y coordinate of 0.69. This indicates that managing the excitons through rational energy level alignment holds the potential for simultaneously satisfying Rec.2020 standard and achieving commercial-level stability.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1. Molecular selection and photophysical properties.
a Molecular structures of PIC-TRZ2, 4CzIPN, and h-BNCO. b Photophysical properties, including the ground-state absorption and PL of PIC-TRZ2, 4CzIPN, and h-BNCO in toluene. c PL of the PIC-TRZ2 neat film, 1 wt% h-BNCO: PIC-TRZ2, and 1 wt% h-BNCO: 8 wt% 4CzIPN: PIC-TRZ2 blend films.
Fig. 2
Fig. 2. Transient PL decay properties.
a The prompt and b the delayed decay properties of 1 wt% h-BNCO: mCBP, 1 wt% h-BNCO: PIC-TRZ2 and 1 wt% h-BNCO: 8 wt% 4CzIPN: PIC-TRZ2 blend films.
Fig. 3
Fig. 3. OLED performance and EL spectra during degradation.
a EL spectra, b EQEs versus luminance curve, and c the operational device stability of D1, D2, and D3, the initial luminance is 1000 cd m−2. The normalized EL spectral shapes of d D1, e D2, and f D3 at various operational lifetimes during the degradation.
Fig. 4
Fig. 4. Charge carrier and exciton dynamics in OLEDs.
a OLED structure of D3 with the thickness of each functional layer. b Energy level alignment and recombination zone distribution of D3. Hole-only device (HOD) and electron-only device (EOD) of the emitter layers in c D2 and d D3. e Transient EL properties of D1, D2, and D3 (the pulsed width was 300 μs). f Transient EL decay properties of D1, D2, and D3 upon switching off the driving voltage.
Fig. 5
Fig. 5. Device performance with the functional layer.
a Illustration of the device structure, carrier transport, exciton generation, energy transfer, and light-emitting process in D3 and D4. b Transient EL excitation properties of D3 and D4. c EQEs versus luminance curves of D3 and D4. The inset is the EL spectrum of D4 at 1000 cd m−2. d Transient EL decay properties of D3 and D4 upon switching off the driving voltage. e Operational device stability of D3 and D4, the initial luminance is 1000 cd m−2. The inset is the operating photograph of D4.
See this image and copyright information in PMC

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