High hole mobility through charge recombination interface in organic light-emitting diodes

Diouf, B.; Jeon, Woo Sik; Park, Jung Soo; Choi, Jin Woo; Son, Young Hoon; Lim, Dong Woo; Doh, Yoo Jin; Kwon, Jang Hyuk

doi:10.1016/j.synthmet.2011.07.025

Cited by 20 publications

(9 citation statements)

References 23 publications

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“…Although Dev.1 and Dev.2 have similar device structures and EL emissions, as shown in Figure a–c, it is anticipated that they have different balancing degrees of charge-carrier injection and thus possess various optoelectronic performances due to their different hole-injection functional layers (HAT-CN and PEDOT:PSS). In Dev.2, the hole-injection barrier (0.6 eV) from PEDOT:PSS to the highest occupied molecular orbital (HOMO) of TCTA molecules is much higher than the electron-injection barrier (0.1 eV) from the LiF/Al cathode to the lowest unoccupied molecular orbital (LUMO) of PO-T2T molecules. − These different barrier heights for the hole and electron injections might cause an unbalanced carrier injection and poor device performance. In contrast, Dev.1 has the hole-injection layer of HAT-CN, which can efficiently reduce the hole-injection barrier, causing a balanced carrier injection and good device performance .…”

Section: Resultsmentioning

confidence: 99%

Room-Temperature Observation for Reverse Intersystem Crossing in Exciplex-Based OLEDs with Balanced Charge Injection

Zhao

Tang

Zhu

et al. 2021

ACS Appl. Electron. Mater.

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Room-temperature observation for reverse intersystem crossing (RISC) from triplet to singlet charge-transfer states (CT 3 → CT 1 ) and clarification of its physical mechanisms are the key requirements for designing highly efficient exciplex-based organic light-emitting diodes (OLEDs). Herein, balanced and unbalanced exciplex-based OLEDs were fabricated by employing different holeinjection layers, and RISC of CT states was directly observed via analyzing magnetoconductance (MC) and magneto-electroluminescence (MEL) traces of the balanced device at room temperature. Specifically, current-dependent MC traces of the balanced device always present B-mediated RISC features, whereas those from the unbalanced one depict the superposition of B-mediated intersystem crossing (ISC) and the dissociation of CT 3 by excessive charge carriers. Simultaneously, MEL curves of the balanced device display the conversion from ISC to RISC with lowering bias current, but those from the unbalanced one always show ISC under all of bias currents. Moreover, although all of current-dependent magneto-efficiency (Mη) traces exhibit ISC, Mη values are ∼2 times lower in the balanced device than the unbalanced one. These rich changes of magnetic-field responses demonstrate that balanced carrier injection can facilitate the occurrence of RISC by reducing the dissociation of CT 3 . Expectedly, the current efficiency of electroluminescence from the balanced device is increased by ∼2.2 times, which originates from the improvement of delayed luminescence because of the enhanced RISC. Accordingly, this work not only clarifies the prerequisite for observing RISC of CT states but also provides strategies for designing high-efficiency exciplex-based OLEDs.

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Section: Resultsmentioning

confidence: 99%

Room-Temperature Observation for Reverse Intersystem Crossing in Exciplex-Based OLEDs with Balanced Charge Injection

Zhao

Tang

Zhu

et al. 2021

ACS Appl. Electron. Mater.

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“…Dopants in this category include 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ; LUMO: −4.6 eV) − and the more widely used 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ; LUMO: −5.24 eV). ,, Following the same concept of molecular design, even higher EA dopants, such as 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F6-TNAP; LUMO: −5.37 eV) , and 3,6-difluoro-2,5,7,7,8,8-hexacyanoquinodimethane (F2-HCNQ; LUMO: −5.59 eV), have been recently synthesized. Other recently reported p-type dopants with high EA include C 60 fullerene (LUMO: −3.6 eV), its fluorinated derivative C 60 F 36 (LUMO: −5.38 eV), , and hexaazatriphenylene hexacarbonitrile (HAT-CN6; LUMO: −5.7 eV). − However, most of these dopants have low solubility in common solvents, and are incorporated into devices structures using either evaporation processes , or premixing in an inert matrix because they cannot be effectively solution processed. This limitation significantly restricts further development of solution-processed and mass-produced organoelectronics applications …”

Section: Introductionmentioning

confidence: 99%

Introducing Solubility Control for Improved Organic P-Type Dopants

et al. 2015

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To overcome the poor solubility of the widely 8 used p-type dopant 2, 3,5,6-tetrafluoro-7,7,8,8-tetracyanoqui-9 nodimethane (F4TCNQ) 31,32 and 3,6-difluoro-2,5,7,7,8,8-75 In this paper, we first demonstrate a straightforward synthetic 88 route to soluble versions of F4TCNQ-type dopants by 89 substituting the cyano groups with either methyl or n-octyl f1 90 esters (Figure 1). A comprehensive study of the electro-91 chemical properties of these F4TCNQ analogues is performed 92 using cyclic voltammetry. With a combination of optical 93 absorption spectroscopy, photoluminescence spectroscopy, and 94 conductivity measurements, we not only demonstrate the p-95 type doping of P3HT using these new dopants, but also show 96 that comparable doping efficiency can be achieved even with 97 slightly reduced electron affinity. These novel molecular 98 dopants establish that the introduction of solubility control is 99 a successful strategy to tailor the properties of organic p-type 100 dopants. 101 ■ EXPERIMENTAL SECTION 102Materials. 1,4-Bis(chloromethyl)-2,3,5,6-tetrafluorobenzene was 103 purchased from Oakwood Products. Sodium hydride (60% dispersion 104 in mineral oil) was purchased from Alfa Aesar. Bromine, 105 perfluorobenzene, potassium carbonate, dimethyl carbonate, malono-106 nitrile, sodium acetate, sodium hydroxide, and phosphorus tribromide 107 were purchased from Sigma-Aldrich. Anhydrous dimethyl sulfoxide 108 (DMSO) and dimethylformamide (DMF) were purchased from Acros 109 Organics. Hydrochloric acid (37% aqueous), p-toluenesulfonic acid 110 monohydrate, ethanol, tetrahydrofuran (THF), dichloromethane 111 (DCM), ethyl acetate, toluene, and hexane were purchased from 112 Fisher Scientific. Acetic acid and sodium cyanide were purchased from 113 Fluka. Octanol was purchased from EM Science. Trifluoroacetic acid 114 (TFA) and acetic anhydride were purchased from EMD. P3HT 115 (Regioregular >98%, M n = 54−75 kDa, HOMO 5 eV and LUMO 3 116 eV) was purchased from Sigma-Aldrich. F4TCNQ (>98%) was 117 purchased from TCI. All chemicals were used as received unless 118 otherwise indicated. All solvents were dried over molecular sieves (3 119 Å) before use. 120Characterization.

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“…The equivalent charge mobility in the DBR films was deduced according to the space charge limited current (SCLC) model, which is usually used to evaluate the charge transport in organic semiconductor films. Based on the Poole–Frenkel equation, the equivalent charge mobility in the devices are field dependent and can be describe as follows:

μ (E) = μ_{0} \exp (β \sqrt{E}) = \frac{8}{9 ϵ_{normalr} ϵ_{0}} \frac{J}{E^{2}}

where μ 0 is the zero‐field mobility and β is the Poole–Frenkel factor. The relative dielectric constant ε r is assumed to be 3 for organic semiconducting materials, and the permittivity of the free space ε 0 is 8.85 × 10 −12 F m −1 .…”

Section: Various Device Structures Of the Multi‐alternating Organic Smentioning

confidence: 99%

“…Generally, a charge recombination and/or generation interface will be formed when the highest occupied molecular orbital (HOMO) of one organic semiconducting material and the lowest unoccupied molecular orbital (LUMO) of another organic semiconducting material are close to each other (for instance, m‐MTDATA and HAT‐CN), which will facilitate the charge transport in the composite films . To improve the conductivity of the hybrid DBRs, we came up with the strategy of utilizing the multi‐alternating organic semiconducting films instead of the single component film as the low‐refractive‐index units.…”

Section: Various Device Structures Of the Multi‐alternating Organic Smentioning

confidence: 99%

Conductive Inorganic–Organic Hybrid Distributed Bragg Reflectors

Shi

Wang

et al. 2015

Advanced Materials

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A conductive hybrid distributed Bragg reflector (DBR) is demonstrated, consisting of inorganic and organic semiconductor films and assembled by a thermal deposition technique. A maximum reflectance of 92.2% and a wide spectral width of more than 70 nm are achieved. The hybrid DBR shows good electrical conductivity, which provides the possibility of practical applications in novel optoelectronic devices, such as electrically pumped organic vertical-cavity surface-emitting lasers.

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High hole mobility through charge recombination interface in organic light-emitting diodes

Cited by 20 publications

References 23 publications

Room-Temperature Observation for Reverse Intersystem Crossing in Exciplex-Based OLEDs with Balanced Charge Injection

Room-Temperature Observation for Reverse Intersystem Crossing in Exciplex-Based OLEDs with Balanced Charge Injection

Introducing Solubility Control for Improved Organic P-Type Dopants

Conductive Inorganic–Organic Hybrid Distributed Bragg Reflectors

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