Abrupt exciton quenching in blue fluorescent organic light-emitting diodes around turn-on voltage region

Kakumachi, Shunta; Nguyen, Thanh Ba; Nakanotani, Hajime; Adachi, Chihaya

doi:10.1016/j.cej.2023.144516

Cited by 6 publications

(3 citation statements)

References 27 publications

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“…The DCM profile for the OLED with TPBi-ETL indicates hole accumulation in the OLED. Since the exciton quenching between the singlet exciton and radical cation at the HTL/EML interface has been reported previously, 26 we speculated that strong unwarranted exciton−polaron quenching occurred at the HTL/EML interface in the OLED with TPBi-ETL. The exciton−polaron annihilation probability should be increased if the carrier recombination zone in the OLED is strongly localized at the carrier-accumulated interface, i.e., the HTL/EML interface.…”

Section: ■ Results and Discussionmentioning

confidence: 61%

Impact of Spontaneous Orientational Polarization on Triplet–Triplet Upconversion-Based Blue Organic Light-Emitting Diodes

Kakumachi,

Nakanotani,

Nagasaki

et al. 2024

ACS Appl. Mater. Interfaces

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The spontaneous orientation polarization (SOP) of a permanent dipole moment of the molecule induces a giant surface potential (GSP) in an organic semiconductor film, and GSP is expected to be a crucial parameter for understanding the operational mechanism of organic light-emitting diodes (OLEDs). This study demonstrates that the voltage-dependent migration of a carrier recombination zone induced by a polar electron transporting layer (ETL) having a positive SOP causes a decline in the overall performance of the OLED in triplet−triplet upconversion (TTU) based on OLEDs. Specifically, the TTU efficiency in an OLED with 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) as the ETL decreased by 20% due to the reduction of electrically generated triplet exciton density. This decrease resulted in a lower external electroluminescence (EL) quantum efficiency (EQE) of 5.4% at 1 mA cm −2 , while the OLED with a nonpolar ETL resulted in an EQE of around 8.1% at 1 mA cm −2 . We confirmed a shift in the recombination zone from the current density dependence of the EL spectra in the OLEDs. Our results indicate that the fixed carrier recombination zone near a hole transport layer and an emitting layer (HTL/EML) strongly enhanced the TTU process, while the polar EML/ETL interface induced the migration of the recombination zone depending on voltage, resulting in the decrease of triplet exciton density.

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Section: ■ Results and Discussionmentioning

confidence: 61%

Impact of Spontaneous Orientational Polarization on Triplet–Triplet Upconversion-Based Blue Organic Light-Emitting Diodes

Kakumachi,

Nakanotani,

Nagasaki

et al. 2024

ACS Appl. Mater. Interfaces

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“…Furthermore because a relatively long exciton lifetime (μs-ms) of TADF emitters is strongly influenced by a voltage applied across the film 35 , a shape of the bias-dependent PL profiles contains a portion of exciton quenching via an applied electric filed (Supplementary Fig. 15c–e ) 36 . Thus, it might be necessary to apply some techniques for the precise identification of the percentage of SOP-induced exciton quenching in TADF-based OLEDs by the bias-dependent PL measurement.…”

Section: Resultsmentioning

confidence: 99%

Simultaneous control of carrier transport and film polarization of emission layers aimed at high-performance OLEDs

Tanaka,

Chan,

Nakanotani

et al. 2024

Nat Commun

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The orientation of a permanent dipole moment during vacuum deposition results in the occurrence of spontaneous orientation polarization (SOP). Previous studies reported that the presence of SOP in organic light-emitting diodes (OLEDs) lowers electroluminescence efficiency because electrically generated excitons are seriously quenched by SOP-induced accumulated charges. Thus, the SOP in a host:guest-based emission layer (EML) should be finely controlled. In this study, we demonstrate the positive effect of dipole-dipole interactions between polar host and polar emitter molecules on the OLED performance. We found that a small-sized polar host molecule that possesses both high molecular diffusivities and moderate permanent dipole moment, well cancels out the polarization formed by the SOP of the emitter molecules in the EML without a disturbance of the emitter molecules’ intrinsic orientation, leading to high-performance of OLEDs. Our molecular design strategy will allow emitter molecules to pull out the full potential of the EMLs in OLEDs.

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“…Organic luminescent materials have attracted extensive attention from researchers in various fields due to their intriguing biocompatibility, structural diversity, and ease of property tuning [9][10][11]. However, traditional organic luminescent materials usually suffer from luminescence quenching at high concentrations or in the aggregated states, which severely limits their practical applications [12][13][14]. Fortunately, Tang et al coined the term "aggregation-induced emission (AIE)" and paved a practical way to enhance the emission efficiency of molecules in the aggregated states [15,16].…”

Section: Introductionmentioning

confidence: 99%

Machine Learning Prediction of Quantum Yields and Wavelengths of Aggregation-Induced Emission Molecules

Bi,

Jiang,

Chen

et al. 2024

Materials

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The aggregation-induced emission (AIE) effect exhibits a significant influence on the development of luminescent materials and has made remarkable progress over the past decades. The advancement of high-performance AIE materials requires fast and accurate predictions of their photophysical properties, which is impeded by the inherent limitations of quantum chemical calculations. In this work, we present an accurate machine learning approach for the fast predictions of quantum yields and wavelengths to screen out AIE molecules. A database of about 563 organic luminescent molecules with quantum yields and wavelengths in the monomeric/aggregated states was established. Individual/combined molecular fingerprints were selected and compared elaborately to attain appropriate molecular descriptors. Different machine learning algorithms combined with favorable molecular fingerprints were further screened to achieve more accurate prediction models. The simulation results indicate that combined molecular fingerprints yield more accurate predictions in the aggregated states, and random forest and gradient boosting regression algorithms show the best predictions in quantum yields and wavelengths, respectively. Given the successful applications of machine learning in quantum yields and wavelengths, it is reasonable to anticipate that machine learning can serve as a complementary strategy to traditional experimental/theoretical methods in the investigation of aggregation-induced luminescent molecules to facilitate the discovery of luminescent materials.

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Abrupt exciton quenching in blue fluorescent organic light-emitting diodes around turn-on voltage region

Cited by 6 publications

References 27 publications

Impact of Spontaneous Orientational Polarization on Triplet–Triplet Upconversion-Based Blue Organic Light-Emitting Diodes

Impact of Spontaneous Orientational Polarization on Triplet–Triplet Upconversion-Based Blue Organic Light-Emitting Diodes

Simultaneous control of carrier transport and film polarization of emission layers aimed at high-performance OLEDs

Machine Learning Prediction of Quantum Yields and Wavelengths of Aggregation-Induced Emission Molecules

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