Three-Dimensional Modeling of Organic Light-Emitting Diodes Containing Molecules with Large Electric Dipole Moments

Coehoorn, R.; Lin, Xin; Weijtens, Christ H. L.; Gottardi, Stefano; Eersel, Harm van

doi:10.1103/physrevapplied.16.034048

Cited by 13 publications

(19 citation statements)

References 63 publications

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“…The intriguing and highly nontrivial time dependence of emission spectra collected in several matrices is quantitatively reproduced, accounting for the subtle interplay among polar solvation dynamics, the nonadiabatic dynamics of conformational degrees of freedom fully accounting for static dielectric and conformational disorder, and the consequent inhomogeneous broadening phenomena. The model, quantitatively validated against experimental photoluminescence data collected in diluted solutions and solid matrices, sets a solid basis to account for environmental effects, including disorder, in phenomenological models for OLED devices. , …”

Section: Introductionmentioning

confidence: 99%

“…The model, quantitatively validated against experimental photoluminescence data collected in diluted solutions and solid matrices, sets a solid basis to account for environmental effects, including disorder, in phenomenological models for OLED devices. 40,41 ■ MATERIALS AND METHODS Molecular Model. As detailed in ref 31 and shortly introduced above, we consider only two electronic basis (diabatic) singlet states, corresponding to the neutral DA state, |N⟩, and to the zwitterionic D + A − state, |Z⟩.…”

Section: ■ Introductionmentioning

confidence: 99%

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Thermally Activated Delayed Fluorescence: Polarity, Rigidity, and Disorder in Condensed Phases

et al. 2022

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We present a detailed and comprehensive picture of the photophysics of thermally activated delayed fluorescence (TADF). The approach relies on a few-state model, parametrized ab initio on a prototypical TADF dye, that explicitly accounts for the nonadiabatic coupling between electrons and vibrational and conformational motion, crucial to properly address (reverse) intersystem crossing rates. The Onsager model is exploited to account for the medium polarity and polarizability, with careful consideration of the different time scales of relevant degrees of freedom. TADF photophysics is then quantitatively addressed in a coherent and exhaustive approach that accurately reproduces the complex temporal evolution of emission spectra in liquid solvents as well as in solid organic matrices. The different rigidity of the two environments is responsible for the appearance in matrices of important inhomogeneous broadening phenomena that are ascribed to the intertwined contribution from (quasi)static conformational and dielectric disorder.

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Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Thermally Activated Delayed Fluorescence: Polarity, Rigidity, and Disorder in Condensed Phases

et al. 2022

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“…Meanwhile, the benefits of SOP in OLEDs are still controversial, e.g., SOP can improve charge injection efficiency and also affect charge blocking property. [ 20–24 ] Thus, exploring methods to control the charge accumulation property while keeping SOP is an important issue to optimize the device performance as well as to understand the role of SOP. In that sense, it will be intriguing to use a device stack with identical (non‐vanishing) SOP in all layers.…”

Section: Introductionmentioning

confidence: 99%

“…Meanwhile, the benefits of SOP in OLEDs are still controversial, e.g., SOP can improve charge injection efficiency and also affect charge blocking property. [20][21][22][23][24] Thus, exploring methods to control the charge accumulation property while keeping SOP is an important issue to optimize the device performance as well as to understand the role of SOP. In that sense, it will be intriguing to use a device stack with identical It is demonstrated that dipolar doping of hole transport layers (HTLs) controls the density and polarity of the accumulated charge at the critical interface between the HTL and the emission layer (EML) in organic lightemitting diodes (OLEDs).…”

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confidence: 99%

Controlling Charge Accumulation Properties of Organic Light‐Emitting Diodes using Dipolar Doping of Hole Transport Layers

Noguchi

Hofmann

Brütting

2022

Advanced Optical Materials

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Although the charge accumulation properties at organic hetero interfaces have been often discussed in terms of the energy barrier to charge injection, it is known that the interface charge due to spontaneous orientation polarization (SOP) also plays a significant role. [5,[9][10][11][12] SOP originates from the macroscopic polarization induced by partial alignment of the permanent dipole moments (PDMs) of polar organic semiconducting materials in evaporated films, [9,13,14] and dominates the charge accumulation properties below the turnon voltage of OLEDs. [5,15,16] SOP has been frequently observed in many common OLED materials, particularly emitters and electron transport materials, though it is very small in most hole transport materials. [5,[17][18][19] Recently, Bangsund et al. have demonstrated that the excess charge accumulation due to SOP can reduce the EQE of OLEDs via exciton-polaron quenching, and EQE can be enhanced by eliminating SOP in the device. [6] Thus far, substrate heating during deposition and use of materials with negligible SOP have been examined to eliminate the excess charge accumulation. [6,7] However, substrate heating can influence the properties of underlayers in the device stack, since SOP is often formed in an emission layer (EML) and electron transport layer (ETL) that are commonly deposited on a hole transport layer (HTL). On the other hand, employing negligible SOP materials limits the possible choice of materials and would not be the best for the overall performance of OLEDs. For instance, many phosphorescent and thermally activated delayed fluorescence emitters also exhibit SOP, and ETL materials with negligible SOP are limited. [5,17] As an alternative method, Afolayan et al. have reported very recently that SOP is efficiently eliminated in a co-evaporated film of ETL and medium density of polyethylene. [8] They demonstrated a higher EQE and longer lifetime of a blue OLED by eliminating the SOP of the ETL. Meanwhile, the benefits of SOP in OLEDs are still controversial, e.g., SOP can improve charge injection efficiency and also affect charge blocking property. [20][21][22][23][24] Thus, exploring methods to control the charge accumulation property while keeping SOP is an important issue to optimize the device performance as well as to understand the role of SOP. In that sense, it will be intriguing to use a device stack with identical It is demonstrated that dipolar doping of hole transport layers (HTLs) controls the density and polarity of the accumulated charge at the critical interface between the HTL and the emission layer (EML) in organic lightemitting diodes (OLEDs). Dipolar doping enables spontaneous orientation polarization (SOP) even in nonpolar HTL, and consequently compensates for the negative interface charge originating from the SOP of the adjacent layer. This concept is applied to a phosphorescent OLED, where bis-4(N-carbazolyl) phenylphosphine oxide (BCPO) is employed as a polar dopant for the HTL. The net interface charge is completely compensated at ≈29.5% of d...

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“…Understanding the charge distributions in the vicinity of the emission layer (EML) of an organic light-emitting diode (OLED) is crucial for improving device performance. − The charge distribution influences both the emission zone and the exciton-polaron quenching (EPQ) probability. Consequently, it also affects the external quantum efficiency (EQE), efficiency roll-off, and device degradation. ,− However, determining the charge distribution in a stacked multilayer OLED is not straightforward, and the influence of the accumulated charges on the optical properties of such a device has been controversial. For instance, the rate constant for triplet-polaron quenching (TPQ), k TP , has been examined in OLEDs as well as in hole-/electron-only devices by many groups.…”

Section: Introductionmentioning

confidence: 99%

Charge-Carrier Dynamics and Exciton-Polaron Quenching Studied Using Simultaneous Observations of Displacement Current and Photoluminescence Intensity

2022

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Herein, we propose a simple but powerful technique for investigating the correlations between the dynamics of charge carriers and excitons. This technique (DCM-PL) is based on displacement current measurement (DCM) with simultaneous observation of the photoluminescence (PL) intensity. By applying this technique to metal–insulator–semiconductor (MIS) devices incorporating a partial stack of a tris(2-phenylpyridine)iridium(III) [Ir(ppy)3]-based organic light-emitting diode (OLED), we are able to investigate the hole accumulation behavior and the corresponding PL losses due to exciton-polaron quenching (EPQ). Remarkably, the DCM-PL characteristics revealed that the polarity of the host material in the emission layer modifies the charge-carrier dynamics and EPQ properties. Our results contribute to the optimization of OLED device performance, since EPQ is a key process involved in efficiency roll-off and device degradation.

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Three-Dimensional Modeling of Organic Light-Emitting Diodes Containing Molecules with Large Electric Dipole Moments

Cited by 13 publications

References 63 publications

Thermally Activated Delayed Fluorescence: Polarity, Rigidity, and Disorder in Condensed Phases

Thermally Activated Delayed Fluorescence: Polarity, Rigidity, and Disorder in Condensed Phases

Controlling Charge Accumulation Properties of Organic Light‐Emitting Diodes using Dipolar Doping of Hole Transport Layers

Charge-Carrier Dynamics and Exciton-Polaron Quenching Studied Using Simultaneous Observations of Displacement Current and Photoluminescence Intensity

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