A Comparison Study of the Organic Small Molecular Thin Films Prepared by Solution Process and Vacuum Deposition: Roughness, Hydrophilicity, Absorption, Photoluminescence, Density, Mobility, and Electroluminescence

Shu, Feng; Duan, Lian; Hou, Lingyun; Qiao, Juan; Zhang, Deqiang; Dong, Guifang; Wang, Liduo; Qiu, Yong

doi:10.1021/jp203674p

Cited by 49 publications

(38 citation statements)

References 32 publications

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“…19 Such photoinitiator undergoes fast homolytic a-cleavage of the carbon-phosphorous bond under UV illumination, which gives rise to two short-lived triplet radicals (t o 1 ns). 20 Photocrosslinking was carried out at 365 nm at room temperature while development was performed at room temperature by using chloroform as a solvent. TPO excitation can indeed severely compete with excitation of fluorophore 8 that displays a lower energy red-emitting excited state.…”

Section: Modular Synthetic Strategymentioning

confidence: 99%

Small molecule-based photocrosslinkable fluorescent materials toward multilayered and high-resolution emissive patterning

et al. 2015

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International audiencea Solution-processable green and red-emitting fluorophores possessing photopolymerizable acrylate units have been synthesized. Photocrosslinking was successfully performed in neat thin films at room temperature under low-dose UV irradiation at 365 nm. No further curing step was necessary to achieve insoluble emissive thin films displaying high optical quality. Up to 80% of the green emitting material processed as a non-doped thin film remained after photopolymerization. Despite competitive energy transfer occurring between the excited photoinitiator and the radiative excited state of red-emitting materials, up to 40% of the initial thickness could be achieved after development. The very low RMS roughness of the green and red photocrosslinked thin films after development (RMS o 0.7 nm) allowed us to fabricate multicolored stacks again with high optical quality (RMS roughness o 1.3 nm) after two cycles of irradiation and development involving successively red and green emitters. Resolved patterns as small as 600 nm in width could be obtained upon photolithography performed under an air atmosphere. High adhesion of the photocrosslinked materials on surfaces makes the resulting emissive thin films very promising for realizing complex emissive structures on flat or bend substrates as required in multiple applications such as optical data storage, organic lasers, organic light emitting diodes or counterfeiting

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Section: Modular Synthetic Strategymentioning

confidence: 99%

Small molecule-based photocrosslinkable fluorescent materials toward multilayered and high-resolution emissive patterning

et al. 2015

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“…One fundamental difference between evaporated and solution processed films is the molecular packing. As summarized in Table S1 of the Supporting Information, it is generally accepted that solution processed organic films have a lower packing density than the vacuum deposited films. 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 .…”

Section: Introductionmentioning

confidence: 99%

“…As summarized in Table S1 of the Supporting Information, it is generally accepted that solution processed organic films have a lower packing density than the vacuum deposited films. 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 . On the other hand, there are only a few reports directly comparing the performance of devices with solution processed and evaporated phosphorescent EMLs, and the root cause for the difference in device performance is not well understood.…”

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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“…These results could contrast at first sight with various reports concluding on the superiority of solution-processed OLEDs over vacuum-deposited ones due to more compact layers obtained for the former upon solution spin-coating. [48][49] In these studies, no photopolymerization was performed, and the emitting or transporting layers were still soluble, precluding further solution deposition for the upper layers.…”

Section: Comparative Solution-processed and Vacuum-evaporated Oled Pementioning

confidence: 99%

All-Solution-Processed Organic Light-Emitting Diodes Based on Photostable Photo-cross-linkable Fluorescent Small Molecules

Derue

Olivier

Tondelier

et al. 2016

ACS Appl. Mater. Interfaces

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We demonstrate herein the fabrication of small molecule-based OLEDs where four organic layers from the hole- to the electron-transporting layers have successively been deposited by using an all-solution process. The key feature of the device relies on a novel photopolymerizable red-emitting material, made of small fluorophores substituted with two acrylate units, and displaying high-quality film-forming properties as well as high emission quantum yield as nondoped thin films. Insoluble emissive layers were obtained upon UV irradiation using low illumination doses, with no further need of postcuring. Very low photodegradation was noticed, giving rise to bright layers with a remarkable surface quality, characterized by a mean RMS roughness as low as 0.7 nm after development. Comparative experiments between solution-processed OLEDs and vacuum-processed OLEDs made of fluorophores with close architectures show external quantum efficiencies in the same range while displaying distinct behaviors in terms of current and power efficiencies. They validate the proof of concept of nondoped solution-processable emissive layers exclusively made of photopolymerized fluorophores, thereby reducing the amount of components and opening the way toward cost-effective fabrication of solution-processed OLED multilayer architectures.

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A Comparison Study of the Organic Small Molecular Thin Films Prepared by Solution Process and Vacuum Deposition: Roughness, Hydrophilicity, Absorption, Photoluminescence, Density, Mobility, and Electroluminescence

Cited by 49 publications

References 32 publications

Small molecule-based photocrosslinkable fluorescent materials toward multilayered and high-resolution emissive patterning

Small molecule-based photocrosslinkable fluorescent materials toward multilayered and high-resolution emissive patterning

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

All-Solution-Processed Organic Light-Emitting Diodes Based on Photostable Photo-cross-linkable Fluorescent Small Molecules

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