Enabling high-efficiency organic light-emitting diodes with a cross-linkable electron confining hole transporting material

Jou, Jwo‐Huei; Li, Tsung-Han; Kumar, Sudhir; An, Chih-Chia; Agrawal, Abhishek; Chen, Sun-Zen; Fang, Po-Hsun; Kručaitė, Gintarė; Grigalevičius, Saulius; Gražulevičius, Juozas V.; Sung, Cheng Kuo

doi:10.1016/j.orgel.2015.06.003

Cited by 41 publications

(20 citation statements)

References 81 publications

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“…Unlike vacuum evaporated OLEDs where a multilayer architecture is easily achieved with sequential deposition, the redissolution of the preceding layer by solvents used in the subsequent layers is a challenge for solution processed OLEDs during the multilayer fabrication process . To get around this problem, cross‐linkable hole transporting layers (HTLs) are typically used such that subsequent deposition of the emitting layer (EML) would not damage the underlying HTL during processing . To finish the device fabrication, evaporated electron transport layers (ETLs) are used in OLED fabrication to avoid solvent damages to the EML.…”

Section: Introductionmentioning

confidence: 99%

Interface Effect on Efficiency Loss in Organic Light Emitting Diodes with Solution Processed Emitting Layers

Chen

Liu

et al. 2016

Adv Materials Inter

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easily achieved with sequential deposition, the redissolution of the preceding layer by solvents used in the subsequent layers is a challenge for solution processed OLEDs during the multilayer fabrication process. [ 4 ] To get around this problem, cross-linkable hole transporting layers (HTLs) are typically used such that subsequent deposition of the emitting layer (EML) would not damage the underlying HTL during processing. [5][6][7][8][9][10][11] To fi nish the device fabrication, evaporated electron transport layers (ETLs) are used in OLED fabrication to avoid solvent damages to the EML.Even with the same multilayer architecture, most OLEDs with a solution processed EML have lower effi ciencies than their thermal-evaporated counterparts. [12][13][14][15][16][17] One fundamental difference between evaporated and solution processed fi lms is the molecular packing. As summarized in Table S1 of the Supporting Information, [16][17][18][19][20][21][22][23][24][25][26] it is generally accepted that solution processed organic fi lms have a lower packing density than the vacuum deposited fi lms. Previous studies comparing solution processed and evaporated OLEDs were mostly focused on HTLs, where the packing density and hence carrier transport plays a critical role. [ 18,20,25,26 ] On the other hand, there are only a few reports directly comparing the performance of devices with solution processed and evaporated phosphorescent EMLs, [ 17,19 ] and the root cause for the difference in device performance is not well understood. It is, therefore, important to identify and study the factors determining the effi ciency loss mechanism in devices with a solution processed EML.In this work, we study the differences in high effi ciency OLEDs having solution processed and thermal-evaporated EMLs. Similar to other fi ndings, we found that the EQE of OLEDs with a solution processed EML is 22% lower than that of the devices with an evaporated EML using 1,3,5tris (N-phenylbenzimidazol-2,yl) benzene (TPBi) as an ETL. Interestingly, this difference in effi ciency became signifi cantly smaller as TPBi was replaced with bis -4,6-(3,5-di-3-pyridylphenyl)-2-methylpyrimidine (B3PYMPM) as an alternative ETL. Because of the deep highest occupied molecular orbital (HOMO) energy of B3PYMPM, we attribute the lower effi ciency in OLEDs with solution processed EMLs to the ineffi cient hole blocking properties of the TPBi ETL as revealed by the single carrier device results. A subsequent study on interfacial exciplex formation and energetic disorder revealed that for devices with a solution processed EML, band tail states broadening along with an energy level shift at the EML/ETL interfaces results in a higherThe performance of multilayered OLEDs with a solution processed emitting layer (EML) is compared to that of counterparts with an evaporated EML and it is found that the interfacial energy changes at the EML and electron transport layer (ETL) interface is a key factor determining the device effi ciency. From the results of exciplex photoluminesc...

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Section: Introductionmentioning

confidence: 99%

Interface Effect on Efficiency Loss in Organic Light Emitting Diodes with Solution Processed Emitting Layers

Chen

Liu

et al. 2016

Adv Materials Inter

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“…We have also studied the effect of employment of a co-host TCTA on the device performance. Additionally, a cross-linkable molecule 3,6-bis(4-vinylphenyl)-9-ethylcarbazole (VPEC) 37 was incorporated as a hole-transport layer, which facilitated layer-by-layer structure via spin-coating and resulted a healthy illumination with less melatonin-suppression, longer retina exposure time, low color temperature, and very-high light-quality. The present study includes human health consideration to the designing process of light source and provide an easy to apply cost-effective fabrication process for an efficient light source.…”

Section: Introductionmentioning

confidence: 99%

High light-quality OLEDs with a wet-processed single emissive layer

Singh

Jou

Sahoo

et al. 2018

Sci Rep

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High light-quality and low color temperature are crucial to justify a comfortable healthy illumination. Wet-process enables electronic devices cost-effective fabrication feasibility. We present herein low color temperature, blue-emission hazards free organic light emitting diodes (OLEDs) with very-high light-quality indices, that with a single emissive layer spin-coated with multiple blackbody-radiation complementary dyes, namely deep-red, yellow, green and sky-blue. Specifically, an OLED with a 1,854 K color temperature showed a color rendering index (CRI) of 90 and a spectrum resemblance index (SRI) of 88, whose melatonin suppression sensitivity is only 3% relative to a reference blue light of 480 nm. Its maximum retina permissible exposure limit is 3,454 seconds at 100 lx, 11, 10 and 6 times longer and safer than the counterparts of compact fluorescent lamp (5,920 K), light emitting diode (5,500 K) and OLED (5,000 K). By incorporating a co-host, tris(4-carbazoyl-9-ylphenyl)amine (TCTA), the resulting OLED showed a current efficiency of 24.9 cd/A and an external quantum efficiency of 24.5% at 100 cd/m2. It exhibited ultra-high light quality with a CRI of 93 and an SRI of 92. These prove blue-hazard free, high quality and healthy OLED to be fabrication feasible via the easy-to-apply wet-processed single emissive layer with multiple emitters.

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“…[17][18][19] Through cross-linking, the functionalm aterials becomei nsoluble in organics olvents, and so the subsequent deposition of anotherl ayer would not corrode the underlying layer.R ecently,s olution-processed multi-layer OLEDs with excellent performance have been reportedb yu sing cross-linkable hole-transportm aterials as well as host materials. [20][21][22][23][24][25][26][27][28][29][30] To the best of our knowledge, there is no report yet on cross-linkable electron-transport materials (ETMs). ETMs with high electron mobility,l ow injection barrier, and strong hole-blocking ability are crucial for high-efficiency OLEDs.…”

Section: Introductionmentioning

confidence: 99%

Highly Air‐Stable Electron‐Transport Material for Ink‐Jet‐Printed OLEDs

Wei

Zhuang

Chen

et al. 2016

Chemistry A European J

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A novel cross-linkable electron-transport material has been designed and synthesized for use in the fabrication of solution-processed OLEDs. The material exhibits a low LUMO level of -3.51 eV, a high electron mobility of 1.5×10 cm V s , and excellent stability. An average 9.3 % shrinkage in film thickness was observed for the film after thermal curing. A maximum external quantum efficiency (EQE) of 15.6 % (35.0 cd A ) was achieved for blue-phosphorescent OLEDs by spin-coating and 13.8 % (31.0 cd A ) for an ink-jet-printed device, both of which are better than the EQE of a control device prepared by vacuum-deposition (see figure).

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Enabling high-efficiency organic light-emitting diodes with a cross-linkable electron confining hole transporting material

Cited by 41 publications

References 81 publications

Interface Effect on Efficiency Loss in Organic Light Emitting Diodes with Solution Processed Emitting Layers

Interface Effect on Efficiency Loss in Organic Light Emitting Diodes with Solution Processed Emitting Layers

High light-quality OLEDs with a wet-processed single emissive layer

Highly Air‐Stable Electron‐Transport Material for Ink‐Jet‐Printed OLEDs

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