Stack design of OLEDs with high performance and simplified device structures

Wang, Jing; Pang, Hai; Cui, Zhihao; Xiao, Changfa; Zheng, Renjie; Kwong, Raymond C.; Xia, Sean

doi:10.1002/jsid.1092

Cited by 5 publications

(10 citation statements)

References 20 publications

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“…However, it is also known that the mobility of holes in most organic materials is one to three orders of magnitude higher than that of electrons [9], which often leads to unbalanced charge transport and an accumulation of excitons near the cathode side of the EML. In particular, it has been proved that the hole injection layer (HIL) strongly affects the hole supply in a device [10][11][12]. We demonstrated in our previous work that the charge balance in an OLED can be improved by modulating the overall hole supply, in particular, through optimizing the HIL [13].…”

Section: Introductionmentioning

confidence: 94%

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11.1: Invited Paper: High Performance Deep Red OLEDs Using Dual p‐dopants to Control Hole Injection

Xie¹,

Pang²,

Wang³

et al. 2023

Symp Digest of Tech Papers

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We demonstrate improved charge balance in organic light emitting devices (OLEDs) by optimizing the hole injection layer (HIL) to control the hole density through the device. Two novel p‐dopants (PDs), PD02 with a shallow lowest unoccupied molecular orbital (LUMO) at ‐4.63 eV (reported in our previous work) and PD03 with a relatively deep LUMO of ‐4.91 eV were used. A two‐layer HIL consisting of HTM:PD02 and HTM:PD03 introduces new design flexibility to improve charge balance in the light emission layer. Using 16% by mass of PD02 and 3% by mass of PD03, we achieve, (1) a bottom emission deep red device with an external quantum efficiency (EQE) of over 30% at a CIE of (0.701, 0.299), an operating voltage of 3.2 V and LT95~13, 000 h at 10 mA/cm2. In particular, the efficiency roll‐off of this device is greatly reduced, which is highly desirable in the display industry. (2) a top emission deep red device with a current efficiency (CE) of 75 cd/A at a CIE of (0.707, 0.293), an operating voltage of 3.6 V and LT95 over 15, 000 h at 10 mA/cm2. An additional benefit from this novel dual p‐doped HIL approach is its much lower lateral conductivity compared to the standard single HIL device structure, resulting in reduced lateral crosstalk between RGB pixels.

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Section: Introductionmentioning

confidence: 94%

“…On the other hand, PD03 is a more effective p-dopant. We measured the lateral conductivity of various HILs using the method reported previously [12]. Their configurations are listed in Table 1.…”

Section: Materials Propertiesmentioning

confidence: 99%

11.1: Invited Paper: High Performance Deep Red OLEDs Using Dual p‐dopants to Control Hole Injection

Xie¹,

Pang²,

Wang³

et al. 2023

Symp Digest of Tech Papers

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“…One indirect way to quantify this is by measuring the conductivity of the composite doped layer. We measured the lateral conductivity of various HIL layers using the method reported in previous work [4], where a 1000 Å thick layer of HTM doped with PD01 or PD02 bridges over 1000 Å thick aluminum (Al) contacts. Table 1 summarizes the calculated conductivity (σ)…”

Section: Materials Propertiesmentioning

confidence: 99%

“…Some holes may transit the EML and leak into the electron conduction side of the device, which is to be avoided. Therefore, the various factors that contribute to the hole supply in an OLED includes the injection properties of the HIL [3,4], the hole mobility and energy level of the HTL [5] and EBL, and the hole transport behavior of the host material along with the trapping characteristics of the emitter in the EML [6] and the energy level of the HBL.…”

Section: Introductionmentioning

confidence: 99%

“…For example, the LUMO of HATCN is -4.33 eV, and that of a typical commercial p-dopant material (PD01) is -5.04 eV. It has also been demonstrated that the energy gap between the LUMO of p-dopant and the HOMO of HTM should be small to ensure efficient hole injection [4]. In contrast, a p-dopant with a shallow LUMO and large energy offset with the HOMO of the HTM tends to result in poor hole injection.…”

Section: Introductionmentioning

confidence: 99%

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45‐1: Invited Paper: Charge Balance in OLEDs: Optimization of Hole‐Injection Layer

Xie¹,

Pang²,

Wang³

et al. 2022

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In this work, we provide a novel strategy to improve the charge balance in organic light emitting devices (OLEDs) by optimizing the hole injection layer (HIL) and thereby controlling the overall hole supply in the device. The lowest unoccupied molecular orbit (LUMO) of the p‐dopant proposed in this work, PD02, is ‐4.63 eV, much shallower than that of the commercial material (PD01). Nevertheless, this enables use of the doping concentration to modulate the supply of holes to the emissive layer to control the charge balance. We demonstrate that device performances are significantly improved by employing such a scheme. With 23% molar doping of PD02, a bottom emission red OLED achieves external quantum efficiency (EQE) over 30%, operating voltage of 3.4 V and LT95 ~ 15,000 h at 10 mA/cm2. Moreover, the efficiency roll‐off is also suppressed up till ~ 3,500 cd/m2, a desirable feature in display applications. A study of exciton distribution within the emissive layer suggests that improved charge balance is indeed achieved in the optimized structure. An additional benefit from the modified HIL is its lower lateral conductivity relative to the standard formula, which reduces crosstalk between RGB pixels.

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Charge balance in OLEDs: Optimization of hole injection layer using novel p‐dopants

Xie,

Pang,

Wang

et al. 2024

J Soc Info Display

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Charge balance is one of the most important factors for realizing high performance organic light emitting devices (OLEDs). In this work, we provide a novel strategy to improve the charge balance in OLEDs by optimizing the hole injection layer (HIL) as well as the electron transporting layer (ETL) and thereby controlling the charge carrier supplies in the device. First, we develop a p‐dopant material (PD02), with a lowest unoccupied molecular orbit (LUMO) of −4.63 eV, much shallower than that of the commercial material (PD01) of which the LUMO is −5.04 eV. Nevertheless, this enables us to modulate the supply of holes to the emissive layer through tuning doping concentration. We demonstrate that device performances are significantly improved by employing such a scheme. With a 23% molar doping of PD02, a bottom emission red OLED achieves an external quantum efficiency (EQE) of over 30%, an operating voltage of 3.4 V and a LT95 ~15,000 h at 10 mA/cm2, with a Digital Cinema Initiative P3 (DCI‐P3) chromaticity of CIE (X, Y) = (0.68, 0.32). Moreover, the efficiency roll‐off is suppressed up till ~3500 cd/m2, a desirable feature in display applications. The lateral conductivity of by using such HIL is also found to be much lower than that of PD01, resulting in reduced crosstalk among RGB pixels. Next, a new electron transporting material (ETM‐02) with a deep LUMO of −2.86 eV is also introduced to further optimize the charge balance. Although devices with ETM‐02 shows lower voltage and higher EQE, lifetime is compromised. In order to improve lifetime, additional fine tuning of the charge balance is essential. Finally, a second p‐dopant PD03 with a LUMO of −4.91 eV is added to the HIL to further extend the modulation flexibility in the hole injection. A double‐layer HIL consisting of 8 nm of HTM:16% PD02 and 2 nm of HTM:3% PD03, where the former is in contact with anode, is adopted in the device structure. The bottom emission deep red device achieve EQE over 30%, an operating voltage of 3.2 V and an improved LT95 ~13,000 h at 10 mA/cm2 with a BT.2020 range chromaticity of CIE (X, Y) = (0.701, 0.299). In the double HIL configuration, the introduction of PD03 provides one more parameter for tuning and therefore improves the overall device performances.

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Stack design of OLEDs with high performance and simplified device structures

Cited by 5 publications

References 20 publications

11.1: Invited Paper: High Performance Deep Red OLEDs Using Dual p‐dopants to Control Hole Injection

11.1: Invited Paper: High Performance Deep Red OLEDs Using Dual p‐dopants to Control Hole Injection

45‐1: Invited Paper: Charge Balance in OLEDs: Optimization of Hole‐Injection Layer

Charge balance in OLEDs: Optimization of hole injection layer using novel p‐dopants

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