Investigation of the hole transport characterization and mechanisms in co-evaporated organic semiconductor mixtures

Wang, Yanping; Liang, Qingcheng; Huang, Jinfeng; Ma, Dongge; Jiao, Yurong

doi:10.1039/c7ra05131j

Cited by 17 publications

(9 citation statements)

References 36 publications

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“…[46,47] Thus, the hole injection from the electrode ITO/HAT-CN to TAPC can realize ohmic contact. The donor materials also act as the holetransporting layer (HTL) and electron blocking layer (EBL), [48,49] while CN-T2T, lithium fluoride (LiF), and aluminum (Al) serve as the electron-transporting layer (ETL), electron injection layer (EIL), and cathode, respectively. Figure 2 shows the EL characteristics of the devices Vis-1 and Vis-2.…”

Section: Resultsmentioning

confidence: 99%

New Exciplex‐Forming Co‐Host System and Thienothiadazole‐based Fluorescent Emitter for High‐Efficiency and Promising Stability Near‐Infrared OLED

Chen

Luo

Wei

et al. 2021

Advanced Optical Materials

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Two new spirobifluorene (SF)‐centered donors (D) DPSF and DTSF are developed to blend with acceptor (A) CN‐T2T for exciplex formation. The transient photoluminescence characterizations of pristine donor and D:A blended films verify the donor aggregates emissions that lead to relatively low photoluminescence quantum yield (PLQY) of exciplex emission. However, the charge recombination at lower energy exciplex state leads the device with DPSF:CN‐T2T blend to give electroluminescence (EL) λmax of 584 nm and external quantum efficiency (EQE) of 6.0%. The DPSF:CN‐T2T exciplex excitons are efficiently extracted by a D‐A‐D‐type fluorescence emitter TTDSF comprising thienothiadiazole core and SF peripherals via Förster energy transfer to give near‐infrared (NIR) emission (760 nm, PLQY 26%). After the electron‐transporting layer thickness optimization, the device with DPSF:CN‐T2T: 7 wt.% TTDSF as emitting layer affords EL λmax 774 nm and EQE up to 5.3%, one of the best cases in NIR organic light‐emitting diodes (OLEDs). More importantly, the device stability has been examined to display an excellent lifetime (LT95 > 200 hours). This work manifests the judicious combination of an exciplex‐forming co‐host system and a designated NIR emitter equipping with a high quinoidal core and rigid peripheral SF groups that can realize an efficient NIR OLED.

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Section: Resultsmentioning

confidence: 99%

New Exciplex‐Forming Co‐Host System and Thienothiadazole‐based Fluorescent Emitter for High‐Efficiency and Promising Stability Near‐Infrared OLED

Chen

Luo

Wei

et al. 2021

Advanced Optical Materials

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“…2 (Figure S3a, Supporting Information). And the hole mobility (≈10 −3 cm 2 V −1 s −1 ) in the HAT-CN/TAPC chargegeneration unit reported in the literature [33] is also equal to the electron mobility (≈10 −3 cm 2 V −1 s −1 ) of PO-T2T. [27]…”

Section: Figure 4bmentioning

confidence: 99%

Conversions from Normal to Abnormal Current‐Dependent ISC and from Abnormal to Normal Current‐Dependent RISC Processes in Exciplex‐Based OLEDs

Zhao

Chen

Tang

et al. 2022

Adv Materials Inter

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Intersystem crossing (ISC) and reverse ISC (RISC) are important spin‐mixing processes for obtaining high quantum efficiency in exciplex‐based organic light‐emitting diodes (EB‐OLEDs) and often show normal current (I) dependencies which weaken with increasing I. Surprisingly, herein, using magneto‐conductance (MC) as a fingerprint probing tool, an unreported conversion from normal to abnormal I‐dependent ISC processes is observed at 300 K from relatively‐unbalanced EB‐OLEDs with the low electron‐injection barrier and the high hole mobility. More amazingly, after improving carrier injection balance through replacing the hole‐injection layer, a conversion from abnormal to normal I‐dependent RISC processes with increasing I is observed from the relatively‐balanced EB‐OLEDs for the first time. These two conversions are reasonably analyzed by fitting and decomposing MC traces of the devices. Furthermore, transition I of the conversion from abnormal to normal I‐dependent RISC processes decreases from 50 to 5 μA as the temperature reduces from 300 to 150 K, and only the normal I‐dependent RISC process is observed at 100 and 20 K due to high driving voltages. Obviously, this work deepens the full understandings of I‐dependent ISC and RISC processes in EB‐OLEDs and has the potential applications for the achievement of high‐performance devices.

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“…The energy level diagram of this hole-only device is shown in Figure . For this junction, a hole barrier of ∼0.6 eV exists at the NPB–CBP interface , and the HOMO level of C545T lies above that of CBP. Thus, C545T serves as energetically favorable hole hopping sites.…”

Section: Introductionmentioning

confidence: 98%

“…Schematic of (a) device structure of the ITO/MoO 3 /NPB/CBP/C545T/MoO 3 /Al hole-only device and (b) corresponding energy level diagram. The HOMO and LUMO energies are taken from refs and .…”

Section: Introductionmentioning

confidence: 99%

Impact of Dopants on Charge Transport across Organic–Organic Semiconductor Junctions

2021

J. Phys. Chem. C

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A typical organic light-emitting diode is made of several functional organic semiconducting layers including a hole transport layer (HTL), an emissive layer (EL) comprising host and dopant molecules, and an electron transport layer. The charge carrier hopping from the HTL into the host–dopant EL is known to control the device performance. Thus, a clear understanding of charge transport physics at the HTL/EL interface is essential to guide selection of organic materials for achieving optimal device performance. In this paper, we report experimental and theoretical studies of electrical characteristics of a variety of HTL/EL junctions. We show that charge transport characteristics at an organic–organic junction vary, depending on the energy level alignments of the dopant to that of the host and HTL. In addition, the dopant concentration is found to dictate the device electrical characteristics. Detailed theoretical studies show that carrier transport across the junction is charge-injection-limited at low dopant concentration (≤2 wt %), while a space-charge-limited injection, that is, Ohmic junction, is obtained at higher dopant concentration.

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Investigation of the hole transport characterization and mechanisms in co-evaporated organic semiconductor mixtures

Abstract: The hole transport characteristics in small molecule semiconductor mixtures of HAT-CN : NPB, HAT-CN : TAPC and HAT-CN : CBP in the ratio of 2 : 1 have been investigated by admittance spectroscopy measurements.

Cited by 17 publications

References 36 publications

New Exciplex‐Forming Co‐Host System and Thienothiadazole‐based Fluorescent Emitter for High‐Efficiency and Promising Stability Near‐Infrared OLED

New Exciplex‐Forming Co‐Host System and Thienothiadazole‐based Fluorescent Emitter for High‐Efficiency and Promising Stability Near‐Infrared OLED

Conversions from Normal to Abnormal Current‐Dependent ISC and from Abnormal to Normal Current‐Dependent RISC Processes in Exciplex‐Based OLEDs

Impact of Dopants on Charge Transport across Organic–Organic Semiconductor Junctions

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