•PGMEA induced P3HT aggregation form bumpy active layer surface.•Active layer self-aggregation improve P3HT crystallinity.•Micro-nanostructured back electrode facilitate charge carriers transfer and enhance light absorption of active layer.•Up to 17.9% PCE improvement achieved in the micro-nanostructured device.The formation of a micro-nanostructured back electrode provides an efficient route for enhancing light absorption in polymer solar cells by light scattering of the bumpy electrode. In this study, we incorporated propylene glycol mono-methyl ether acetate (PGMEA) into the poly (3-hexylthiophene) (P3HT) and [6:6]-phenyl-C61-butyric acid (PC61BM) solution, and the PGMEA induced P3HT aggregations give rise to a bumpy surface of the active layer. The sequential deposition of the Al electrode onto the active layer creates a polymer solar cell with interpenetrated micro-nanostructured morphology of the active layer/electrode interface. The higher crystallinity of P3HT induced by active layer self-aggregation improves carrier mobility. The bumpy active layer/electrode interface can not only facilitate charge carriers transfer and collection in the device, but also enhance optical scattering and leads to enhanced light absorption of the active layer. The resulting device shows improved photocurrent, corresponding to power conversion efficiency improvement of 17.9% as compared to the planar device. This work indicates that the active layer self-aggregation is a simple, cost-effective and mold-free methodology to manufacture high performance polymer solar cells with the micro-nanostructured back electrode.

Ligand-free rutile and anatase TiO2 nanocrystals have been synthesized through a hydrolytic sol–gel reaction. The morphology, crystal structure, elemental composition and band structure of the obtained nanocrystals are characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and UV-visible absorption spectroscopy. These two kinds of nanocrystals could serve as electron extraction layers for improving the performance in inverted polymer solar cells. Compared with the device fabricated by using amorphous TiO2 (6.11%) and rutile TiO2 (6.93%), the device based on anatase TiO2 shows a significant enhancement in power conversion efficiency (7.85%). Meanwhile, the ideal current–voltage model for a single heterojunction solar cell is applied to clarify the junction property of the cell. The model demonstrates that the device based on anatase TiO2 has effective electron extraction and hole-blocking properties.

Low dark current density plays a key role in determining the overall performance of organic photodetectors (OPDs). However, both the donor domains and acceptor domains in the bulk heterojunction, which has high exciton dissociation efficiency, are in contact with the two electrodes. Therefore, the undesirable charge injection from the electrodes to the active layer is hard to avoid, leading to a high dark current density in most OPDs. In this work, we fabricate the OPDs based on a conventional poly(3-hexylthiophene) (P3HT)/(phenyl-C61-butyric-acid-methyl-ester) (PC61BM) bulk heterojunction. By incorporating a water/alcohol soluble conjugated polymer (WSCP), poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN), interlayer between the anode and the active layer, the dark current density is effectively reduced from 0.07 mA cm−2 to 1.92 × 10−5 mA cm−2 under a −0.5 V bias. The resulting OPDs show a 1.93 × 105 signal-to-noise ratio (SNR), a 10 MHz bandwidth, and a 9.10 × 1012 Jones detectivity at a low reverse bias of −0.5 V (at 550 nm). Our research provides a promising way for high performance OPDs.

•Excimer emission is observed in the solid doped and un-doped poly-TPD film.•Monomer, excimer and electromer emission are obtained in the devices with single-layer poly-TPD or bilayer poly-TPD/TPBi.•Single electromer emission is acquired in TPBi doped poly-TPD OLEDs.•Electromer emission is increased under high TPBi contentation and electric field.The effect of 1,3,5-Tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi) doping on electroluminescent properties of poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (poly-TPD) was investigated. A series of organic light-emitting devices (OLEDs) integrated with (i) single-layer poly-TPD, (ii) blended single-layer poly-TPD:TPBi or (iii) bilayer poly-TPD/TPBi were fabricated and characterized. An excimer emission band at 500 nm was found in the poly-TPD film, poly-TPD:TPBi (1:1) blend film, and poly-TPD/TPBi bilayer film. It was observed that the planar geometry of poly-TPD was related to the formation of excimers. The electromer emission, which was absent in photoluminescence, was investigated by applying an external electrical field to devices with non-doped and TPBi-doped poly-TPD. Only the electromer emission was observed in the devices with TPBi-doped poly-TPD, due to the impeded intrinsic and excimer emissions. The planar geometry of poly-TPD molecules may be destroyed due to the longer inter-ion distance with the doping of TPBi.

In this study, large-sized silver nanoparticles (Ag NPs) (average size: 80 nm) have been introduced into the anodic buffer poly-(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer (thickness: about 55 nm) of poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester bulk heterojunction polymer solar cells. The results showed that the short-circuit current density can increase from 8.73 to 11.36 mA/cm2, and power conversion efficiency increases from 2.28 to 2.65 % when 0.1 wt% Ag NPs was incorporated in PEDOT:PSS layer, corresponding to an efficiency improvement of 16.2 %. Absorption spectrums of the active layers indicate that large-sized Ag NPs have no clear contribution to optical absorption improvement. By measuring the conductivity of PEDOT:PSS films without and with Ag NPs and analyzing device structure of this polymer solar cell, it was founded that the improvements in power conversion efficiency was originated from higher conductivity of PEDOT:PSS layer incorporated with Ag NPs and the shorter routes for holes to travel to the anode.

•AlPcCl as an anode buffer layer was introduced in OLED.•The performance of OLED with AlPcCl is superior to that of the device without AlPcCl.•The enhanced performance is explained by energy level and thermionic emission model.•The effect of the deposition rate of AlPcCl on the device performance was examined.•The optimal deposition rate of AlPcCl is 0.05 nm/s.The characteristics of organic light-emitting diodes (OLEDs) with aluminum phthalocyanine chloride (AlPcCl) as an anode buffer layer were investigated. The basic structure of OLED is indium-tin oxide (ITO)/N,N′-di(naphth-2-yl)-N,N′-diphenyl-benzidine (NPB)/tris(8-hydroxyquinoline) aluminum (Alq3)/lithium fluoride (LiF)/aluminum (Al). AlPcCl inserted at the ITO/NPB interface as an anode buffer layer can enhance hole injection, and thus current density, luminance as well as efficiency. Based on the energy level and Richardson–Schottky (R–S) thermionic emission theory, the enhanced performance can be explained. Additionally, the effect of the deposition rate of AlPcCl on the device performance was also examined. The results show that the optimal deposition rate of AlPcCl is 0.05 nm/s.

Different thicknesses of cesium chloride (CsCl) and various alkali metal chlorides were inserted into organic light-emitting diodes (OLEDs) as electron injection layers (EILs). The basic structure of OLED is indium tin oxide (ITO)/N,N′-diphenyl-N,N′-bis(1-napthyl-phenyl)-1.1′-biphenyl-4.4′-diamine (NPB)/tris-(8-hydroxyquinoline) aluminum (Alq3)/Mg:Ag/Ag. The electroluminescent (EL) performance curves show that both the brightness and efficiency of the OLEDs can be obviously enhanced by using a thin alkali metal chloride layer as an EIL. The electron injection barrier height between the Alq3 layer and Mg:Ag cathode is reduced by inserting a thin alkali metal chloride as an EIL, which results in enhanced electron injection and electron current. Therefore, a better balance of hole and electron currents at the emissive interface is achieved and consequently the brightness and efficiency of OLEDs are improved.Highlights► Alkaline metal chlorides were used as electron injection layers in organic light-emitting diodes based on Mg:Ag cathode. ► Brightness and efficiency of OLEDs with alkaline metal chlorides as electron injection layers were all greatly enhanced. ► The Improved OLED performance was attributed to the possible interfacial chemical reaction. ► Electron-only devices are fabricated to demonstrate the electron injection enhancement.

We report an efficient hole injection layer (HIL) composed of MoO3-doped C60 for organic light-emitting diodes (OLED). The structure of the OLED device is ITO/MoO3:C60 (5 nm:5 nm)/NPB (45 nm)/Alq3 (55 nm)/LiF (0.5 nm)/Al. Compared with normal device without a HIL, the device using MoO3-doped C60 as HIL can significantly enhance both hole injection efficiency and electroluminescence. The power efficiency has been increased by approximately 40.7% and 41.7% at the current density of 10 mA/cm2 and 100 mA/cm2, respectively, for the device using MoO3-doped C60 as HIL than the control device. The cause for the enhancement was ascribed to the charge transfer complex formed by co-evaporation of MoO3 and C60. Hole-only devices were fabricated to confirm the hole injection enhancement. Ultraviolet/visible/near-infrared absorption spectra were measured to confirm the formation of the charge transfer complex.Highlights► MoO3-doped C60 is used as an efficient hole injection layer for OLED. ► Driving voltage is significantly reduced and luminance is greatly enhanced. ► Power efficiency is increased by more than 40% at 10 and 100 mA/cm2, respectively. ► The enhancement is ascribed to charge transfer complex formed between MoO3 and C60.

A multilayer organic light-emitting diode (OLED) with favorable performance was fabricated via using sodium triphosphate (Na3PO4) material as an efficient electron injection layer. Luminance and efficiency of the devices are notably improved due to a thin Na3PO4 layer inserted between electron transport layer (ETL) and aluminum cathode. The optimal thickness of electron injection layer is confirmed to be 1 nm, and the electroluminescent efficiency of OLED reaches 3.5 cd/A. The role of Na3PO4 was investigated on the enhanced performance of OLED through X-ray photoelectron spectroscopy (XPS). The effect of different positions of Na3PO4 layer inside Alq3 layer on the performance of OLED was systematically studied. By comparing with the devices based on ETL/Na3PO4/Al, ETL/LiF/Al and ETL/NaCl/Al, the electroluminescent efficiency of Na3PO4-based device is the highest. Na3PO4 as electron injection material has a promising potential application in OLED.Highlights► Na3PO4 as an electron injection layer in OLED improve the device performance. ► The optimal thickness of Na3PO4 as an electron injection layer in OLED is 1 nm. ► The suitable position of Na3PO4 is the interface of Alq3 and Al cathode. ► The enhanced properties of OLED with Na3PO4 are explained by XPS. ► Na3PO4 as an electron injection layer can be comparable with LiF and NaCl.

The operating voltage is reduced and luminous efficiency is improved in the organic light-emitting diodes (OLEDs) with UV–ozone treatment of molybdenum trioxide (MoO3) anode buffer layer. The interface of indium tin oxide (ITO)/MoO3 was investigated by X-ray photoelectron spectroscopy. It was found that the binding energies of Mo 3d, O 1s, In 3d and C 1s were shifted to higher after UV–ozone treated MoO3. The enhanced properties are impervious to the UV–ozone treatment of ITO. Therefore, the improved performance can be attributed that the binding energies of Mo 3d, O 1s, In 3d and C 1s are changed to higher and also that the sheet resistance of ITO/MoO3 films is decreased after UV–ozone treated MoO3.Highlights► The performance of OLED is improved by O3 treatment of molybdenum trioxide (MoO3). ► The enhanced performance can be due to the change of ITO/MoO3 sheet resistance. ► The improvement of performance is also due to oxidation by O3 treatment of MoO3. ► XPS shows the binding energy of Mo 3d after O3 treated MoO3 are shifted to higher.

Photovoltaic performance of bulk heterojunction polymer solar cells (PSCs) based on poly(3-hexylthiophene) as donor and [6,6]-phenyl-C61-buytyric acid methyl ester as acceptor was improved by using a thin 8-hydroxyquinolatolithium (Liq) interlayer between polymer active layer and Al counter-electrode. By using 1.0 nm Liq, power conversion efficiency (PCE) of the PSC significantly increased to 3.20%, in comparison with a PCE of 2.40% for the PSC without Liq buffer layer. The PCE enhancement was primarily beneficial from the obviously increased short circuit current density, open circuit voltage and fill factor. This improvement is ascribed to the interfacial dipole effect, a better ohmic conductivity and the suppression of leakage current, which are all introduced by the Liq buffer layer.Highlights► 8-hydroxyquinolatolithium as efficient electron buffer layer in polymer solar cells. ► Short circuit current density, open circuit voltage, fill factor were all increased. ► Power conversion efficiency significantly increased from 2.40 % to 3.20 %. ► Improvement due to interfacial dipole effect and suppressed leakage current.

We have introduced graphdiyne material in poly(3-hexylthiophene)/[6,6]-phenyl-C61-buytyric acid methyl ester bulk-heterojunction solar cells. The results suggest that the doping of graphdiyne can improve the short circuit current (Jsc) and power conversion efficiency (PCE) of the polymer solar cells. The cell with 2.5 wt% graphdiyne exhibits an enhanced Jsc by 2.4 mA/cm2 and the highest PCE (3.52%), which is 56% higher than that of the cell without graphdiyne doping. The improved performance is due to high charge transport capability of graphdiyne and the formation of efficient percolation paths in the active layer.Highlights► Graphdiyne doping enhanced the short circuit current of PSCs. ► The doping ratio of graphdiyne plays an important role in the performance of PSCs. ► The efficient percolation path improve the transportation efficiency of charge.

In poly(3-hexylthiophene) (P3HT) mixed with [6,6]-phenyl-C61-buytyric acid methyl ester (PCBM) bulk-heterojunction solar cells, organic small molecular pentacene was introduced as dopant in P3HT:PCBM active layer. The results suggest that the doping of pentacene can improve the short circuit current (Jsc) and power conversion efficiency (PCE) of the polymer solar cells. The cell with 0.4 wt.% pentacene exhibits an enhanced Jsc by 2.08 mA/cm2 and the highest PCE (2.36%), which is 20% higher than that of the cell without pentacene doping. The improved performance is mainly due to efficient dissociation of exciton in active layer caused by pentacene doping.Highlights► Pentacene doping enhanced the short circuit current of PSCs. ► The doping ratio of pentacene plays an important role in the performance of PSCs. ► The absorption of pentacene doping in active layer nearly unchanged. ► The well aligned energy levels improve the dissociation efficiency of exciton.

The performance of organic light-emitting diodes (OLED), based on NPB/Alq3/KCl/Alq3 active regions, with various anode (i.e. ITO and ITO/MoO3) and cathode (i.e. Al and LiF/Al) structures is compared. NPB, Alq3, KCl, ITO, MoO3, Al and LiF are N,N′-bis-(1-naphthl)-diphenyl-1,1′-biphenyl-4,4′-diamine, tris (8-hydroxyquinoline) aluminum, potassium chloride, indium-tin oxide, molybdenum trioxide, aluminum and lithium fluoride, respectively. When bare Al is used as a cathode, both luminance and efficiency are improved by the insertion of KCl inside Alq3 (anode/NPB/Alq3/KCl/Alq3/Al), compared to a control device (anode/NPB/Alq3/Al). This is attributed to trap sites induced by KCl layer, which give a better recombination in the devices. However, if the cathode is LiF/Al, the performance of control device (anode/NPB/Alq3/LiF/Al) is superior to that of devices with KCl inside Alq3 (anode/NPB/Alq3/KCl/Alq3/LiF/Al), which is attributed that the probability of electron injection from cathode is decreased.Research highlights► We examine the effect of electrode on the performance of OLED with KCl inside Alq3. ► The anode includes ITO and ITO/MoO3; the cathodes are Al and LiF/Al. ► The cathode has a great influence on the improving properties of KCl inside Alq3. ► The enhancing properties of KCl in OLED are unsusceptible to the anode. ► KCl has two effects: trap hole; decrease the probability of electron injection.

It has been studied that the effect of different electron transporting materials, including 2-(4-biphenyl)-5-(4-tert-butylphenyl)1,3,4-oxidiazole (PBD), tris-8-hydroxy-quinolinato aluminum and Bis[2-(2-benzothiazoly)phenolato]zinc(II) on the properties of solar cells based on poly(3-hexylthiophene) and [6,6]-phenyl-C61-buytyric acid methyl ester composites. The results suggest that the insertion of electron transporting layers (ETL) can improve the open circuit voltage (Voc) and power conversion efficiency (PCE) of the polymer solar cells. And the effect of thickness of the three ETL has also been investigated. The cell with a PBD layer exhibits an enhanced Voc by 0.16 V and the highest PCE, which is 1.6 times that of the cell without ETL. The improved performance is due to the increased built-in potential in the interface between the active layer and Al electrode.

A novel structure of organic light-emitting diode was fabricated by inserting a molybdenum trioxide (MoO3) layer into the interface of hole injection layer copper phthalocyanine (CuPc) and hole transport layer N,N′-diphenyl-N,N′-bis(1-napthyl–phenyl)-1,1′-biphenyl-4,4′-diamine (NPB). It has the configuration of ITO/CuPc(10 nm)/MoO3(3 nm)/NPB(30 nm)/ tris-(8-hydroxyquinoline) aluminum (Alq3)(60 nm)/LiF(0.5 nm)/Al. The current density–voltage–luminance (J–V–L) performances show that this structure is beneficial to the reduction of driving voltage and the enhancement of luminance. The highest luminance increased by more than 40% compared to the device without hole injection layer. And the driving voltage was decreased obviously. The improvement is ascribed to the step barrier theory, which comes from the tunnel theory. The power efficiency was also enhanced with this novel device structure. Finally, “hole-only” devices were fabricated to verify the enhancement of hole injection and transport properties of this structure.

Organic light-emitting diodes (OLEDs) were fabricated based on copper phthalocyanine (CuPc) (hole-injecting layer), N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) (hole-transporting layer) and tris(8-hydroxyquinoline) aluminum (Alq3) (emission and electron-transporting layer). A 2-(4-biphenylyl)-5(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) layer was inserted between CuPc and NPB. The effect of different thickness of PBD layer on the performance of the devices was investigated. The device structure was ITO/CuPc/PBD/NPB/Alq3/LiF/Al. Optimized PBD thickness was about 1 nm and the electroluminescent (EL) efficiency of the device with 1 nm PBD layer was about 48 percent improvement compared to the device without PBD layer. The inserted PBD layer improved charge carriers balance in the active layer, which resulted in an improved EL efficiency. The performance of devices was also affected by varying the thickness of NPB due to microcavity effect and surface-plasmon loss.

A multilayer organic light-emitting diode (OLED) has been fabricated with a thin (1 nm) potassium chloride (KCl) layer inserted inside an electron transport layer (ETL), tris (8-hydroxyquinoline) aluminum (Alq3). The structure of device was ITO/NPB/Alq3/KCl/Alq3/Al. The KCl layer was inserted inside 60 nm Alq3 at 10, 20 and 30 nm positions away from the Alq3/Al interface. The device shows the optical power and electroluminescence (EL) efficiency enhancements. The highest optical power density of devices with KCl at different positions is more than twice as high as that of the device without KCl. The EL efficiency is enhanced by more than 50% by inserting the thin KCl insulating layer. The mechanism of KCl EL efficiency enhancer is that the thin KCl layer induces carrier trap sites and gives better recombination in the device. After air-exposure 42 h, the efficiency of the devices with KCl is enhanced but not for the device without KCl. The insertion of KCl inside Alq3 may improve the stability of OLED.

A multilayer organic light-emitting diode (OLED) was fabricated with a thin rubidium chloride (RbCl) layer inserted inside an electron transport layer (ETL), tris (8-hydroxyquinoline) aluminum (Alq3). Here, we set d is the distance of the RbCl layer away from the Alq3/Al interface. The rubidium chloride layer was inserted inside 60 nm Alq3 at d = 0.0, 2.5, 5.0, 7.5, 10, 20 and 30 nm positions. When the RbCl layer is positioned closer to the Al cathode, both the current density and EL efficiency are enhanced due to the enhanced electron injection. The devices show the electroluminescent (EL) efficiency improvement without an enhanced injection if the value of d is lager than 5.0 nm. The suggested mechanism of RbCl EL efficiency enhancer is carrier trap sites induced by the thin RbCl layer. The trapped charges alter the distribution of the field inside the OLED and, consequently, give better recombination in the device.

The effect of indium-tin oxide (ITO) surface treatment on hole injection of devices with molybdenum oxide (MoO3) as a buffer layer on ITO was studied. The Ohmic contact is formed at the metal/organic interface due to high work function of MoO3. Hence, the current is due to space charge limited when ITO is positively biased. The hole mobility of N, N′-bis-(1-napthyl)-N, N′-diphenyl-1, 1′biphenyl-4, 4′-diamine (NPB) at various thicknesses (100–400 nm) has been estimated by using space-charge-limited current measurements. The hole mobility of NPB, 1.09×10−5 cm2/V s at 100 nm is smaller than the value of 1.52×10−4 cm2/V s at 400 nm at 0.8 MV/cm, which is caused by the interfacial trap states restricted by the surface interaction. The mobility is hardly changed with NPB thickness for the effect of interfacial trap states on mobility which can be negligible when the thickness is more than 300 nm.

We report on the fabrication of organic light-emitting diodes (OLEDs) using a zinc acetate ((CH3COO)2Zn) layer as the cathode buffer layer. The results show that the device containing a (CH3COO)2Zn interlayer shows improved luminance and efficiency due to the Zn–N bond formation resulting in the occurrence of Alq3 anion and also due to the band bending at the Alq3/Al interface, which is beneficial to electron injection by lowering electron injection barrier. And the devices with structured cathodes (CH3COO)2Zn/LiF/Al and LiF/(CH3COO)2Zn/Al have a higher luminance and efficiency than the LiF/Al cathode-based device.

In this letter, we have fabricated an efficient, color stable white organic electroluminescent device through the incorporation of double thin 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) emitting layers and 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB), a hole transporting and blue emitting material. The device structure is ITO/NPB 45 nm/DCJTB 0.15 nm/NPB 5 nm/DCJTB 0.15 nm/BCP 10 nm/AlQ 50 nm/LiF 0.3 nm/Al 150 nm. This device exhibited a pure white-light emission having Commission Internationale de I’Eclairage (CIE) coordinates of (0.324, 0.336), a current efficiency of 2.9 cd/A and a maximum brightness of 7016 cd/m2. When the current density increased from 2 mA/cm2 to 100 mA/cm2, we observed only a slight shifting in the CIE coordinates from (0.324, 0.336) to (0.320, 0.326). Moreover, the efficiency of the device with double thin emitting layers of DCJTB is two times higher than the device with only one DCJTB layer.

A thin layer of samarium (Sm) was introduced in the cathode fabrication of the organic light-emitting devices (OLEDs). An efficient cathode Sm/LiF/Al used to improve the performance of OLEDs was reported. Standard N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl 4,4′-diamine (NPB)/tris-(8-hydroxyquinoline) aluminum (AlQ) devices with Sm/LiF/Al cathode showed dramatically enhanced electroluminescent (EL) brightness and efficiency. The optimized device with the 0.5 nm layer of Sm with the cathode structure of Sm/LiF/Al showed the improved power efficiency of 40% than the control device of the conventional LiF/Al cathode at 100 mA/cm2. The drive voltage of the device with the Sm/LiF/Al cathode was decreased about 2 V at 500 mA/cm2 compared with the conventional LiF/Al cathode device. The enhanced properties of the device with such a multilayer cathode are considered to the improved balance of electron/hole injection in the emitting layer.

In this letter, bright non-doped red to yellow organic light-emitting diodes (OLEDs) with ultrathin 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) layer as the emitting layer were fabricated. It was investigated that the effect of the ultrathin DCJTB layer on the electroluminescent (EL) performance of OLEDs. The DCJTB layer was incorporated at different positions in the conventional tris(8-quinolinolato)-aluminum (AlQ)-based devices (ITO/NPB/AlQ/LiF/Al). The emission of DCJTB was dominative in the EL spectra of the devices, in which the position of 0.3 nm DCJTB layer was less than 10 nm from the NPB/AlQ interface. The EL peak emission of DCJTB shifted to blue side as DCJTB position moved gradually from AlQ to NPB layer. The highest brightness of the device with 0.3 nm DCJTB layer inserted into NPB reached 16,200 cd/m2 at 15 V, with the CIE coordinates of (0.522, 0.439).