DCJTB Layer Research Articles

Study on interface engineering of layer-by-layer structure for applications in organic photodetector

The interfacial electronic structure of layer-by-layer 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB)/fullerene C60 was investigated using ultra-violet photoemission spectroscopy (UPS). Photoemission data of period of DCJTB/C60/DCJTB films suggested the formation of surface dipole and interfacial band bending across the interfaces, which greatly facilitates the charge transfer from DCJTB to C60 and from C60 to DCJTB layer as well. When applied this layer-by-layer structure to a near-infrared photodetector, a maximum of photocurrent was achieved by the device with 3 periods of DCJTB/C60 thin films. Finally, the detailed work mechanism of this detector was discussed.

A novel red organic light-emitting diode with ultrathin DCJTB and Rubrene layers

A novel red organic electroluminescent diode based on an ultrathin 4-(dicyanomethylene)-2- t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) layer has been fabricated. The device with the ultrathin DCJTB layer inserted between N, N′-bis-(1-naphthyl)- N, N′-diphenyl-1,1′-biph-enyl-4,4′- diamine (NPB) and tri-(8-hydroxyquinoline) aluminum (Alq 3) layers has an emission from both DCJTB and Alq 3. When utilizing the 5,6,11,12-tetraphenylnaphthacene (Rubrene) bilayer as the emitting-assistant layer in the fabrication of the device, the emission from Alq 3 disappears. We attribute the improvement of color purity to the exciton confinement and energy transfer from the Rubrene molecular. The device with 0.1 nm DCJTB layer has a luminance of 1130 cd/m 2 at 20 mA/cm 2 with an EL efficiency of 5.6 cd/A, and the CIE coordinates was [0.617, 0.379]. The maximum brightness of this device reaches 21,525 cd/m 2.

Detailed analysis of ultrathin fluorescent red dye interlayer for organic photovoltaic cells

The influence of an ultrathin 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) fluorescent dye layer at donor/acceptor heterojunction on the performance of small-molecule organic photovoltaic (OPV) cell is studied. The structure of OPV cell is of indium-tin oxide (ITO)/copper phthalocyanine (CuPc)/DCJTB/fullerene (C60)/bathophenanthroline (Bphen)/Ag. The results show that open circuit voltage (VOC) increases to 0.57 V as the film thickness of DCJTB layer increases from 0.2 to 2.0 nm. By using an equivalent circuit model, the enhancement of VOC is found to be attributed to the reduced reverse saturation current density (JS) which is due to the lower highest occupied molecular orbital (HOMO) level in DCJTB than that in CuPc. Also, the short circuit current density (JSC) is affected when the DCJTB layer becomes thicker, resulting from the high series resistance RSA due to the low charge carrier mobility of fluorescent red dye.

The mechanism of efficiency enhancement with proper thickness of DPVBi layer for blue organic light-emitting devices (BOLED)

We report on the fabrication of blue organic light-emitting devices (BOLEDs) with structure: ITO/NPB/DPVBi/Alq 3/LiF/Al. The hole-blocking effect in NPB/DPVBi interface was indirectly demonstrated and deduced by inserting DCJTB layer. In addition, the effect of the device with better J– V characteristics because of the extra DCJTB layer is discussed as well. However, the performance of devices was investigated with various thicknesses of DPVBi layer. The result shows that the device with proper thickness of DPVBi layer generating better electron injection enhances efficiency and luminance for BOLED.

Non-doped red to yellow organic light-emitting diodes with an ultrathin 4-(dicyanomethylene)-2- t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) 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/m 2 at 15 V, with the CIE coordinates of (0.522, 0.439).

White organic light emitting devices with thin 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) layer

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 45nm/DCJTB 0.15nm/NPB 5nm/DCJTB 0.15nm/BCP 10nm/AlQ 50nm/LiF 0.3nm/Al 150nm. 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 2.9cd/A and a maximum brightness of 7016cd/m2. When the current density increased from 2mA/cm2 to 100mA/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.

Improvement of color purity in white OLED based on Zn(HPB) 2 as blue emitting layer

We synthesized zinc (II) [2-(2-hydroxyphenyl)benzoxazole] (Zn(HPB) 2) as blue emitting materials and evaluated in the organic light emitting diodes (OLEDs). The layer of Zn(HPB) 2 doped with 4-(dicyanomethylene)-2- t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) (Zn(HPB) 2:DCJTB) as emitters has been demonstrated. The structure of the device is indium–tin–oxide (ITO)/ N,N′-bis-(1-naphthl)-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB, 40 nm)/Zn(HPB) 2/Zn(HPB) 2:DCJTB/Alq 3 (20 nm)/LiF/Al. The thickness of Zn(HPB) 2 layer was 0, 10, 20, 30 nm at the same time the thickness of Zn(HPB) 2:DCJTB layer were 40, 30, 20, 10 nm. When thickness of Zn(HPB) 2 layer was 30 nm and the thickness of Zn(HPB) 2:DCJTB layer was 10 nm, white emission is achieved. The Commission Internationale de l'Eclairage (CIE) coordinates of the white emission are (0.304, 0.332) at an applied voltage of 10.5 V.

The carrier-trapping effect of dye doped in Alq

The electroluminescence (EL) of an organic light-emitting diode specially fabricated with a pure thin dye layer 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) of 1-nm thickness inserted at the interface between N,N′-bis-(1-naphthl)-diphenyl-1,1′-biphenyl-4,4′-diamine and tris(8-quinolinolato) aluminum has been investigated. The EL behavior of this device changed dramatically at a driving voltage of about 12.25V, which has been ascribed to the breakage of the thin DCJTB layer. It is suggested that not only such thin layer of DCJTB can transport electrons and holes, but also trap them. A comparison of the EL performance with four other devices confirms this mechanism. Therefore, the high efficiency and long life of the dye doped Alq devices are attributed to the hole and electron trapping effect and the high photoluminescence efficiency of the dye.

Nondoped-type red organic electroluminescent devices based on a 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran ultrathin layer

Nondoped-type red organic electroluminescent devices based on a 4-(dicyanomethylene) -2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) ultrathin layer have been fabricated. When the ultrathin DCJTB layer is inserted between N, N′-bis-(1-naphthyl)-N, N′-diphenyl-1,1′-biph-enyl-4,4′-diamine (NPB) and tri-(8-hydroxyquinoline) aluminium (Alq3) (type A device), the emission from Alq3 is mixed with the emission from DCJTB and the colour purity of the device becomes poor. When utilizing the Alq3 (5 nm)/TPBI (45 nm) (TPBI: 2,2′,2″-(1,3,5-phenylene)tris (1-phenyl-1 H-benzimidazole)) bilayer as a hole/exciton blocking and electron transporting layer (type B device), the emission from Alq3 disappears. We attribute it to the excitons confinement effect by the Alq3 (5 nm)/TPBI (45 nm) bilayer. The type B device with 0.2 nm DCJTB has a maximum efficiency of 2.20 cd A−1 and a luminance of 280 cd m−2 is achieved at 20 mA cm−2 with an EL efficiency of 1.41 cd A−1, and the CIE coordinates are (0.628, 0.369).

Trap effect of an ultrathin DCJTB layer in organic light-emitting diodes

An improved performance of organic light-emitting diodes has been obtained by using 4-(dicyanomethylene)-2- t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4 Hpyran (DCJTB) as an ultrathin emitting layer. When 0.1 nm DCJTB was inserted between the hole-transporting layer and electron-transporting layer, for an unoptimized device indium–tin oxide (ITO)/naphtylphenyliphenyl diamine (NPB)/DCJTB (0.1 nm)/8-hydroxyquinoline aluminum (Alq 3)/Al, the maximum brightness was 1531 cd m −2 at 15 V. Compared with doped devices ITO/NPB/Alq 3:DCJTB (1%)/Alq 3/LiF/Al, a higher efficiency has been achieved. Compared with the conventional device ITO/NPB/Alq 3/Al, the inserted device has a slightly higher current efficiency and lower turn-on voltage. We suggest the ultrathin DCJTB layer acts as trap for carriers, and the accumulated holes at the hole-transport layer/electron-transport layer interface have enhanced the electric field in the electron-transport layer and improved the electron injection at the cathode.