Improved electron injection in all-solution-processed n-type organic field-effect transistors with an inkjet-printed ZnO electron injection layer

Roh, Jeongkyun,Kim, Hyeok,Park, Myeongjin,Kwak, Jeonghun,Lee, Changhee Elsevier 2017 APPLIED SURFACE SCIENCE - Vol.420 No.-

<P><B>Abstract</B></P> <P>Interface engineering for the improved injection properties of all-solution-processed n-type organic field-effect transistors (OFETs) arising from the use of an inkjet-printed ZnO electron injection layer were demonstrated. The characteristics of ZnO in terms of electron injection and transport were investigated, and then we employed ZnO as the electron injection layer via inkjet-printing during the fabrication of all-solution-processed, n-type OFETs. With the inkjet-printed ZnO electron injection layer, the devices exhibited approximately five-fold increased mobility (0.0058cm<SUP>2</SUP>/Vs to 0.030cm<SUP>2</SUP>/Vs), more than two-fold increased charge concentration (2.76×10<SUP>11</SUP> cm<SUP>−2</SUP> to 6.86×10<SUP>11</SUP> cm<SUP>−2</SUP>), and two orders of magnitude reduced device resistance (120MΩcm to 3MΩcm). Moreover, n-type polymer form smoother film with ZnO implying denser packing of polymer, which results in higher mobility.</P> <P><B>Highlights</B></P> <P> <UL> <LI> ZnO was used to modify electrode-semiconductor interface property. </LI> <LI> ZnO was deposited through inkjet printing, and worked as an electron injection layer. </LI> <LI> Injection property of the OFETs was greatly improved with inkjet-printed ZnO. </LI> <LI> Electron mobility of the OFETs was boosted by five-fold with inkjet-printed ZnO. </LI> <LI> n-type polymer, P(NDI2OD-T2), forms smooth and dense film on ZnO. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

전자 주입층이 유기EL소자 효율에 미치는 영향

최경훈 ( Kyung Hoon Choi ),손병청 ( Byung Chung Sohn ),김영관 ( Young Kwan Kim ) 한국유화학회 2002 한국응용과학기술학회지 Vol.19 No.4

N/A We investigated the effec of electron injection layer on the performance of organic light emitting devices (OLEDs), As an electron injection layer, the quinolate metal complexes were used. We optimized the device efficiency by varying the thickness of the quinolate metal complexes layer. The device with 1 nm of the quinolate metal complexes layer showed significant enhancement of the device performance and device lifetime. We also compared the effect of 8-hydroxyquinolinolatolithium (Liq) with that of bis(8-quinolinolato)-zinc (Znq_2) and 8-hydroxyquinolinolatosodium (Naq) as an electron injection layer. As a result, Liq is considered as a better materials for the electron injection layer than Znq_2 and Naq.

Performance of Three-Layered Organic Light-Emitting Diodes Using the Hole-Transport and Injection Layer of TPD and Teflon-AF, and the Electron-Injection Layer of Li₂CO₃ and LiF

Shin, Jong Yeol,Kim, Tae Wan,Kim, Gwi Yeol,Lee, Su Min,Hong, Jin Woong The Korean Institute of Electrical and Electronic 2017 Transactions on Electrical and Electronic Material Vol.18 No.2

The performance of three-layered organic light-emitting diodes (OLEDs) was investigated using TPD hole-transport and injection layers, Teflon-AF, and the electron-injection layer of $Li_2CO_3$ and LiF. The OLEDs were manufactured in a structure of TPD/$Alq_3$/LiF, TPD/$Alq_3$/$Li_2CO_3$, and AF/$Alq_3$/LiF using low-molecular organic materials. In three different three-layered OLEDs, it was found that the device with the TPD/$Alq_3$/LiF structure shows higher performance in maximum luminance, and maximum external quantum efficiency compared to those of the device with TPD/$Alq_3$/$Li_2CO_3$ and TPD/$Alq_3$/LiF by 35% and 17%, and 193% and 133%, respectively. It is thought that the combined LiF/Al cathode contributes to a reduced work function and improves an electrical conduction mechanism due to the electron injection rather than the hole transport, which then increases a recombination rate of charge carriers.

Performance of Three-Layered Organic Light-Emitting Diodes Using the Hole-Transport and Injection Layer of TPD and Teflon-AF, and the Electron-Injection Layer of Li2CO3 and LiF

신종열,김태완,김귀열,이수민,홍진웅 한국전기전자재료학회 2017 Transactions on Electrical and Electronic Material Vol.18 No.2

The performance of three-layered organic light-emitting diodes (OLEDs) was investigated using TPD hole-transportand injection layers, Teflon-AF, and the electron-injection layer of Li2CO3 and LiF. The OLEDs were manufactured in astructure of TPD/Alq3/LiF, TPD/Alq3/Li2CO3, and AF/Alq3/LiF using low-molecular organic materials. In three differentthree-layered OLEDs, it was found that the device with the TPD/Alq3/LiF structure shows higher performance inmaximum luminance, and maximum external quantum efficiency compared to those of the device with TPD/Alq3/Li2CO3 and TPD/Alq3/LiF by 35% and 17%, and 193% and 133%, respectively. It is thought that the combined LiF/Al cathode contributes to a reduced work function and improves an electrical conduction mechanism due to theelectron injection rather than the hole transport, which then increases a recombination rate of charge carriers.

Efficiency and Lifetime Improvement of Organic Light- Emitting Diodes with a Use of Lithium-Carbonate- Incorportated Cathode Structure

Rang Kyun Mok,김태완 한국전기전자재료학회 2012 Transactions on Electrical and Electronic Material Vol.13 No.2

Enhancement of efficiency and luminance of organic light-emitting diodes was investigated by the introduction of a lithium carbonate (Li2CO3) electron-injection layer. Electron-injection layer is used in organic light-emitting diodes to inject electrons efficiently between a cathode and an organic layer. A device structure of ITO/TPD (40 nm)/Alq3 (60 nm)/Li2CO3 (x nm)/Al (100 nm) was manufactured by thermal evaporation, where the thickness of Li2CO3layer was varied from 0 to 3.3 nm. Current density-luminance-voltage characteristics of the device were measured and analyzed. When the thickness of Li2CO3 layer is 0.7 nm, the current efficiency and luminance of the device at 8.0V are improved by a factor of about 18 and 3,000 compared to the ones without the Li2CO3 layer, respectively. The enhancement of efficiency and luminance of the device with an insertion of Li2CO3 electron-injection layer is thought to be due to the lowering of an electron barrier height at the interface region between the cathode and the emissive layer. This is judged from an analysis of current density-voltage characteristics with a Fowler-Nordheim tunneling conduction mechanism model. In a study of lifetime of the device that depends on the thickness of Li2CO3 layer, the optimum thickness of Li2CO3 layer was obtained to be 1.1 nm. It is thought that an improvement in the lifetime is due to the prevention of moisture and oxygen by Li2CO3 layer. Thus, from the efficiency and lifetime of the device, we have obtained the optimum thickness of Li2CO3 layer to be about 1.0 nm.

Efficiency and Lifetime Improvement of Organic Light- Emitting Diodes with a Use of Lithium-Carbonate- Incorportated Cathode Structure

Mok, Rang-Kyun,Kim, Tae-Wan The Korean Institute of Electrical and Electronic 2012 Transactions on Electrical and Electronic Material Vol.13 No.2

Enhancement of efficiency and luminance of organic light-emitting diodes was investigated by the introduction of a lithium carbonate ($Li_2CO_3$) electron-injection layer. Electron-injection layer is used in organic light-emitting diodes to inject electrons efficiently between a cathode and an organic layer. A device structure of ITO/TPD (40 nm)/$Alq_3$ (60 nm)/$Li_2CO_3$ (x nm)/Al (100 nm) was manufactured by thermal evaporation, where the thickness of $Li_2CO_3$ layer was varied from 0 to 3.3 nm. Current density-luminance-voltage characteristics of the device were measured and analyzed. When the thickness of $Li_2CO_3$ layer is 0.7 nm, the current efficiency and luminance of the device at 8.0 V are improved by a factor of about 18 and 3,000 compared to the ones without the $Li_2CO_3$ layer, respectively. The enhancement of efficiency and luminance of the device with an insertion of $Li_2CO_3$ electron-injection layer is thought to be due to the lowering of an electron barrier height at the interface region between the cathode and the emissive layer. This is judged from an analysis of current density-voltage characteristics with a Fowler-Nordheim tunneling conduction mechanism model. In a study of lifetime of the device that depends on the thickness of $Li_2CO_3$ layer, the optimum thickness of $Li_2CO_3$ layer was obtained to be 1.1 nm. It is thought that an improvement in the lifetime is due to the prevention of moisture and oxygen by $Li_2CO_3$ layer. Thus, from the efficiency and lifetime of the device, we have obtained the optimum thickness of $Li_2CO_3$ layer to be about 1.0 nm.

Hole transport improvement in CdZnO/ZnO light emitting diodes with wedge shaped electron blocking layers

Kim Jong-Ryeol 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.82 No.10

Carrier transport characteristics of current injected II-VI CdxZn1−xO∕ZnO quantum well (QW) light emitting diodes (LEDs) were theoretically studied, by using both conventional square shaped and wedge-shaped electron blocking layers (EBLs). CdZnO∕ZnO QW LEDs with wedge EBL layers exhibited a much improved hole injection rate compared to LEDs with square EBL layers. By the enhanced hole injection efciency, a balance in the injected electron and hole concentrations are promoted. Therefore, the radiative recombination rate is signifcantly enhanced in the LEDs with wedge-shaped EBL. In addition, we observed that the insertion of the wedge-shaped EBL signifcantly reduces the efciency droop which is the reduction of internal quantum efciency (IQE) with increasing injection current density. It is expected that the CdZnO∕ZnO QW LED with a wedge-shaped EBL is advantageous for the high power light emission via the minimization of efciency droop, especially in the high injection current range.

Improved performance of organic light-emitting diodes with cesium chloride inside tris (8-hydroxyquinoline) aluminum

Zhaoyue Lü,Zhenbo Deng,Zheng Chen,Hailiang Du,Ye Zou,Denghui Xu,Yongsheng Wang 한국물리학회 2011 Current Applied Physics Vol.11 No.3

A series of small molecular organic light-emitting diodes (OLEDs) based on tris (8-hydroxyquinoline)aluminum (Alq_3) was fabricated by varying thicknesses and positions of cesium chloride (CsCl) layer inside Alq_3 layer. Both luminance and efficiency are enhanced due to the improvement of electron injection when a CsCl layer was deposited between Alq3 and aluminum (Al). For the insertion of the CsCl layer at the 10 nm position inside Alq3 layer away from Al cathode, the enhanced current density and luminance are attributed to the reaction between diffused Al and Cs. And the efficiency and luminance are enhanced due to the trap sites induced by the CsCl layer at the distance of 20 and 30 nm away from the Al cathode. The current density and luminance of devices, in which various thicknesses of CsCl layer was inserted at 20 nm position inside Alq3 layer away from the Al cathode, is affected by both hole trapped and insulating layer effects.

Efficient Inverted Bottom-emission Blue Phosphorescent Organic Light-emitting Diodes with a Ytterbium-doped Electron Injection Layer

이현구,Hyuk Ahn,이창희,곽정훈 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.9

An efficient electron injection layer (EIL) for the inverted bottom-emission organic light-emitting diodes (IBE-OLEDs) is developed by doping ytterbium (Yb) into an organic electron transport material of 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene (TmPyPB). The Yb-doped EIL in the IBE-OLEDs having iridium(III) bis(4,6-(difluorophenyl)pyridinato-N,C<SUP>2’</SUP>) picolinate (FIrpic) as a blue phosphorescent dopant show a lower turn-on voltage (~4.5 V) and about 6.6 times higher efficiency (~8.6 % and 15.3 cd/A at 0.15 mA/cm<SUP>2</SUP>) compared with the device without the Yb-doped EIL. Furthermore, the electroluminescence spectrum of the device with the Yb-doped EIL is about the same as that of the device without the Yb-doped EIL. This result indicates that the Yb-doped EIL improves the electron injection from the ITO cathode to an organic electron transport layer. Therefore, the Yb-doped EIL can be utilized as an effective electron injection layer in the OLEDs.

Nonconjugated Anionic Polyelectrolyte as an Interfacial Layer for the Organic Optoelectronic Devices

Lim, Gyeong Eun,Ha, Ye Eun,Jo, Mi Young,Park, Juyun,Kang, Yong-Cheol,Kim, Joo Hyun American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.14

<P>A nonconjugated anionic polyelectrolyte, poly(sodium 4-styrenesulfonate) (PSS-Na), was applied to the optoelectronic devices as an interfacial layer (IFL) at the semiconducting layer/cathode interface. The ultraviolet photoelectron spectroscopy and the Kelvin probe microscopy studies support the formation of a favorable interface dipole at the organic/cathode interface. For polymer light-emitting diodes (PLEDs), the maximum luminance efficiency (LE<SUB>max</SUB>) and the turn-on voltage (<I>V</I><SUB>on</SUB>) of the device with a layer of PSS-Na spin-coated from the concentration of 0.5 mg/mL were 3.00 cd/A and 5.5 V, which are dramatically improved than those of the device without an IFL (LE<SUB>max</SUB> = 0.316 cd/A, <I>V</I><SUB>on</SUB> = 9.5 V). This suggests that the PSS-Na film at the emissive layer/cathode interface improves the electron injection ability. As for polymer solar cells (PSCs), the power conversion efficiency (PCE) of the device with a layer of PSS-Na spin-coated from the concentration of 0.5 mg/mL was 2.83%, which is a 16% increase compared to that of the PSC without PSS-Na. The PCE improvement is mainly due to the enhancement of the short-circuit current (12% increase). The results support that the electron collection and transporting increase by the introduction of the PSS-Na film at the photoactive layer/cathode interface. The improvement of the efficiency of the PLED and PSC is due to the reduction of the Schottky barrier by the formation of a favorable interface as well as the better Ohmic contact at the cathode interface.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-14/am400478b/production/images/medium/am-2013-00478b_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am400478b'>ACS Electronic Supporting Info</A></P>