Fabrication of Alq3／PBD OMQW Structures and Its Photoluminescence Characteristics

Organic multiple quantum well(OMQW)structures consisting of alternating layers of tris(8-quinolinolato)aluminum(Ⅲ）（Alq3)an 2-(4-biphenylyl)-5-(4-ter-butylphenyl)-(1,3,3-oxadiazole)(PBD)have been fabricated by organic molecular beam deposition(OMBD).The individual layer thickness in the multilayer samples was varied from 6 nm tp 20nm.The multiple quantum well structures were determined by low angle X-ray diffraction,optical absorption and photoluminescence(PL).The PL spectra narrow and the emission energy has been observed to shift to higher energy compared with that in the monolayer structure,suggesting a quantum size effect.     

Energy transfer in organic multilayer quantum well structure and its application to OLEDs

We fabricate a series of samples and OLEDs with organic multilayer quantum well structure, which consist of alternate PBD and Alq3. Both PBD and Alq3 are electron-transporting materials, and PBD is used as potential barrier layer, while Alq3 is used as potential well layer and emitting layer. Compared with double-layer structure, the luminescent characteris- tics of organic samples and diodes with quantum well structure are investigated and the quantum well structure helps the energy transfer between well layer and barrier layer. The quantum well structure makes carriers disperse in the different well layers and then increases the number of excitons to enhance the efficiency of the recombination.     

Film thickness effect on the performance of small molecular solar cell

An efficient organic photovoltaic (OPV) cell with an indium-tin-oxide/CuPc/C60/Ag structure has been investigated by changing the film thickness of organic layers. A high open-circuit voltage (VOC) of 0.5 V,a short-circuit current density (JSC) of 5.81 mA/cm2,and a high power conversion efficiency (ηp) of 1.2% were achieved at an optimum film thickness. The results demonstrate that material thickness is an important factor to cell optimization,especially for maximizing the absorp-tion rate as well as reducing the cell resistance. Experimental results also indicate that the power conversion efficiency increases from 1.2% to 1.54% as a BCP exciton blocking layer of 10 nm is introduced.     

Blue and green organic light-emitting devices with various film thicknesses for color tuning

Blue and green organic light-emitting devices with a structure of indium tin oxide (ITO) /N,N’-bis-(1-naphthyl)-N,N’- diphenyl-1,1’-biphenyl-4,4’-diamine (NPB)/aluminum(III) bis(2-methyl-8-quinolinato)4 –phenylphenolato (BAlq) /tris(8- hydroxyquinolate)-aluminum (Alq3)/Mg:Ag have been fabricated. Blue to green light emission has been achieved with the change of organic film thickness. Based on energy band diagram and charge carrier tunneling theory, it is concluded that the films of different thicknesses play a role as a color-tuning layer and the color-variable electroluminescence (EL) is ascribed to the modulation function within the charge carrier recombination zone. In the case of heterostructure devices with high performance, the observed EL spectra varies significantly with the thickness of organic films, which is resulted from the shift of recombination region site. It has not been hitherto indicated that the devices compose of identical components could be implemented to realize different color emission by changing the film thickness of functional layers.     

Film thickness effect on the performance of small molecular solar cell

An efficient organic photovoltaic （OPV） cell with an indium-tin-oxide/CuPc/C60/Ag structure has been investigated by changing the film thickness of organic layers. A high olin-circuit voltage （Yoc） of 0.5 V, a short-circuit current density （Jsc） of 5.81 mA/cm^2, and a high power conversion efficiency （ηp） of 1.2% were achieved at an optimum film thickness. The results demonstrate that material thickness is an important factor to cell optimization, especially for maximizing the absorption rate as will as reducing the cell resistance. Experimental results also indicate that the power conversion efficiency increases from 1.2% to 1.54% as a BCP exciton blocking layer of 10 nm is introduced.     

The strong absorption characteristics of ternary one-dimensional photonic crystals with silver layer

In order to achieve broadband and efficient optical absorption, the multiple silver nanolayer was introduced into the photonic crystals to form a one-dimensional ternary periodic symmetric structure. The effects of thickness of each layer on the band range, absorption bandwidth, absorbance and absorption energy field distribution of the solar spectrum high absorption band were studied by the transfer matrix method. The absorption band with wavelength range from 724 nm to 1 188 nm, spectral width of 464 nm, and average absorbance of 0.78 was obtained by structural adjustment. The absorbed energy is mainly distributed in the first half of the symmetrical structure of the photonic crystal. When the thickness of the silver layer decreased from 30 nm to 15 nm, the local energy in each period increased significantly. At the same time, the distribution and transfer of energy in silicon and MgF2 layers can be controlled. The results of this paper can be used to improve the absorption of solar radiation, and provide an important basis for the design of photonic crystal and their application in solar energy utilization.     

Enhanced performance of C60 organic field effect transistors using a tris(8-hydroxyquinoline) aluminum buffer layer

We have investigated the properties of C60-based organic field effect transistors（OFETs） with a tris（8- hydroxyquinoline） aluminum（Alq3） buffer layer inserted between the source/drain electrodes and the active material. The electrical characteristics of OFETs are improved with the insertion of Alq3 film.The peak field effect mobility is increased to 1.28×10^-2 cm²/（V·s） and the threshold voltage is decreased to 10 V when the thickness of the Alq3 is 10 nm.The reason for the improved performance of the devices is probably due to the prevention of metal atoms diffusing into the C60 active layer and the reduction of the channel resistance in Alq3 films.     

Effect of BCP ultrathin layer on the performance of organic light-emitting devices

Based on conventional double layer device, triple layer organic light-emitting diodes (OLEDs) with two heterostructures of indium-tin oxide (ITO)/N,N'-diphenyl-N,N'-bis(1-naphthyl)(1,1'-biphenyl)-4,4'-diamine(NPB)/2,9-dimethyl-4,7-diphenyl- 1,10-phenanthroline (BCP)/ 8-Hydroxyquinoline aluminum (Alq3)/Mg:Ag using vacuum deposition method have been fabricated. The influence of different film thickness of BCP layer on the performance of OLEDs has been investigated. The results showed that when the thickness of the BCP layer film gradually varied from 0.1 nm to 4.0 nm, the electrolumines- cence (EL) spectra of the OLEDs shifted from green to greenish-blue to blue, and the BCP layer acted as the recombination region of charge carriers related to EL spectrum, enhancing the brightness and power efficiency. The power efficiency of OLEDs reached as high as 7.3 lm/W.     

Effect of BCP ultrathin layer on the performance of organic light-emitting devices

Based on conventional double layer device, triple layer organic light-emitting diodes （OLEDs） with two heterostructures of indium-tin oxide （ITO）/N,N＇-diphenyl-N,N＇-bis（1-naphthyl）（1,1 ＇-biphenyl）-4,4＇-diamine（NPB）/2,9-dimethyl-4,7-diphenyl- 1,10-phenanthroline （BCP）/8-Hydroxyquinoline aluminum （Alq3）/Mg：Ag USing vacuum deposition method have been fabricated. The influence of different film thickness of BCP layer on the performance of OLEDs has been investigated. The results showed that when the thickness of the BCP layer film gradually varied from 0.1 nm to 4.0 nm, the electroluminescence （EL） spectra of the OLEDs shifted from green to greenish-blue to blue, and the BCP layer acted as the recombination region of charge carriers related to EL spectrum, enhancing the brightness and power efficiency. The power efficiency of OLEDs reached as high as 7.3 lm/W.     

Fabication of Organic／Polymeric Superlattice Structure and Its Use for Electroluminescent Device^①②

Superlattices consisting of alternating layers of organic/polymeric materials have been fabricated from tris(8-hydroxyquinoline) aluminum(Alq3) and poly(N-vinylcarbazole)(PVK) by a multisource-type high-vacuum organic molecular deposition.The characteristics of superlattice structures are determined by the smallangle X-ray diffraction,optical adsorption and photoluminescence.The electroluminescent devices with the superlattice structure have also been fabricated and the emission characteristics are discussed.     

有机／聚合物双异质结发光二极管

报道了用有机／聚合物薄膜材料制备的双异质结发光二极管。器件结构为：玻璃衬底／ＩＴＯ／ＰＶＫ／ＡｌｑＰＢＤ／Ａｌｑ３／Ａｌ电极。在这种结构器件中，电子和空穴分别从Ａｌ负电极和ＩＴＯ正电极中注入，产在ＰＢＤ及ＰＶＫ中传输注入到Ａｌｑ３发光层中。器件在正向偏压为４Ｖ时有绿色光输出；在正向偏压为１０Ｖ，最大亮度可达３０００ｃｄ／ｍ＾２以上。经光谱测试，电致发光峰值波长为５２３ｎｍ。     

一种有机多层量子阱结构能量转移的研究

将有机材料PBD和Alq3交替生长，制备PBD／Alq3有机多层量子阱结构（OMQWs）。利用电化学循环伏安法和光吸收分别测定PBD和Alq3最低空分子轨道（LUMO）和最高占据分子轨道（HOMO）。从能带图可看出，类似于无机半导体中的Ⅰ型量子阱结构。利用小角X射线衍射（XRD）和荧光光谱研究了OMQWs的结构特征和光致发光特性。本文基于四个周期制备了不同势垒层和势阱层厚度的样品。随着势垒层厚度地变化，PBD与Alq3之间的能量转移也有所变化，文中将给与讨论。     

C_(60)作激子阻挡层的有机发光二极管

制备了结构为ITO/CuPc(25nm)/NPB(40nm)/Alq3(xnm)/C60(ynm)/LiF(1nm)/Al(100nm)的有机发光二极管(OLEDs),研究了C60插入层对器件性能的影响。结果表明,在无C60的器件中,当Alq3层较厚时,器件的电流密度-电压(J-V)曲线右移,不利于获得高功率效率;当Alq3层较薄时,又会导致激子在LiF/Al阴极的严重淬灭。实验优化得出,在无C60的器件中,Alq3厚为45nm的器件可获得最高的功率效率。在Alq3与LiF之间插入15nmC60层后,对器件的J-V曲线几乎没有影响,但C60层阻挡了激子向阴极扩散,减少了淬灭。当在Alq3厚度为45nm的器件的Alq3和LiF间插入15nmC60层后,可使器件获得更高的功率效率,尤其是插入15nmC并将Alq厚度降至30nm,获得了最大的功率效率。     

Organic light-emitting devices with a 2-(4-biphenyl)-5-(4-butylphenyl)-1,3,4-oxadiazole layer between the α-naphtylphenyliphenyl diamine and 8-hydroxyquinoline aluminum

Organic light-emitting devices (OLEDs) with a 2-(4-biphenyl)-5-(4-butylphenyl)-1,3,4-oxadiazole layer between the α-naphtylphenyliphenyl diamine and 8-hydroxyquinoline aluminum were fabricated using a vacuum evaporation method. Compared to the different thickness of the buffer layer, the OLEDs with the 1.0 nm buffer layer showed the maximum power efficiency. The enhancements in power efficiency result from an improved balance of hole and electron injections. After comparing among different density buffer layer, PBD are good candidates for hole-injecting buffer layer, and 1.0 nm PBD buffer layer shows better operational durability and life.     

Organic small-molecule heterointerface for use in transistor-type non-volatile memory

A chargeable layer is an essential element for charge transfer and trapping in a transistor-based non-volatile memory device. Here we demonstrate that a heterointerface layer comprising of two different small molecules can show electrical memory characteristics. The organic heterointerface layer was fabricated with a pentacene and tris(8-hydroxyquinoline) aluminum (Alq3) layers by sequential vapor deposition without breaking the vacuum state. Pentacene was adopted as the active layer on the top, and Alq3 was used as the bottom layer for charge trapping. The bottom-gate top-contact transistor with an organic heterointerface layer showed distinct non-volatile memory behaviors and showed high air stability and reliability. We investigated the energy structure of the pentacene/Alq3 heterointerface layer to reveal the operation mechanism of the non-volatile memory and suggested that the writing/erasing gate bias-dependent energy barrier originating from the difference between the energy levels of the pentacene and Alq3 layers controls the charge transfer at the heterointerface layer. Our approach suggests a simple way to fabricate heterointerface layers for organic non-volatile memory applications with high air stability and reliability.     

8-羟基喹啉铝作为修饰层对C60有机场效应管性能影响的研究

采用真空蒸镀技术制备了以喹啉铝(tris(8-hydroxyquinoline) aluminum, Alq3)作为修饰层的C60有机场效应管器件,并研究了修饰层的厚度对于器件性能的影响。实验表明,随着Alq3修饰层厚度的增加,器件的性能参数得到改进。当Alq3修饰层厚度为10nm时,器件场效应的迁移率达到最大值,为1.2810-2cm2/Vs,阈值电压也下降到了10V。分析了缓冲层使器件性能提高的主要原因可能有两个：一个是可以阻止金属原子扩散进入C60有机层,另一个是使Al/C60界面间的沟道电阻降低。     

有机缓冲层(Alq3和PBD)和无机缓冲层(TiO2)对OLEDs的不同影响

制备了三种不同缓冲层材料(TiO2、Alq3和PBD)修饰ITO的有机电致发光器件,同没有缓冲层修饰的器件相比,亮度和效率都有很大改善.同时通过比较有缓冲层修饰的三个器件的启亮电压和器件的效率,发现TiO2材料修饰的器件的启亮电压最低(为4 V),效率最高,在电流密度为120 mA/cm2情况下电流效率为5 cd/A;Alq3修饰的器件启亮电压次之(为5V),在相同电流密度下电流效率为4.5 cd/A;PBD材料修饰的器件启亮电压最高(为6 V),相同电流密度下电流效率为3 cd/A.因为ITO表面不平整,缓冲层的修饰使ITO表面得到了改善,由于TiO2的最优化厚度比Alq3和PBD的最优化厚度大,所以对于ITO表面的平整作用也就相应的要强.同时,空穴在有机材料和无机材料中的传输过程是不一样的,有机分子间的电荷移动靠的是分子离化,而无机材料中电荷的转移主要靠的是带传导.而且三种材料HOMO能级也不一样,TiO2材料的HOMO能级(7.2 eV)最高.因此,三个材料中TiO2对于空穴的阻挡作用最大,通过隧穿作用穿过缓冲层材料PBD的空穴数就小于缓冲层材料Alq3和PBD,TiO2修饰的器件的载流子的平衡程度就高于Alq3和PBD修饰的器件,从而效率也相应的高于Alq3和PBD修饰的器件.     

Novel Heterolayer Organic Light‐Emitting Diodes Based on a Conjugated Dendrimer

We demonstrate a novel organic light‐emitting diode (LED) heterolayer structure that contains a conjugated dendrimer as the light‐emitting molecule. The LED was prepared by spin‐coating two dendrimer layers from the same solvent. The device consists of a graded bilayer structure formed from a neat dendrimer film covered with a film consisting of the same dendrimer but doped with the electron‐transporting material 2‐(4‐biphenylyl)‐5‐phenyl‐1,3,4‐oxadiazole (PBD). In this device, the heterojunction interface present in conventional bilayer organic light‐emitting diodes is eliminated, and is replaced by a graded interlayer. By optimizing the concentration of PBD in the dendrimer, a peak electroluminescence (EL) external quantum efficiency of 0.16 % at 600 cd m^–2 was obtained. The EL quantum efficiency is significantly enhanced in comparison with devices based on a single layer, a conventional bilayer, and a single‐layer doped with PBD. The EL quantum efficiency is a factor of eight larger than that of a conventional bilayer LED made with the conjugated dendrimer as the emissive layer and poly(methylmethacrylate) (PMMA) doped with PBD as the electron‐transporting layer. The best blended device exhibited only one third of the efficiency of the graded device. The improvement in the operating characteristics of the graded device is attributed to the efficient device structure, in which exciton formation is improved by a graded doping profile of electron‐ and hole‐transporting components.