基于空间电荷限制电流模型的FeCl3掺杂CBP的空穴迁移率研究

基于不同浓度FeCl3掺杂的4,4′-N,N′-二咔唑基联苯(CBP)设计制作了一系列的单空穴有机电致发光器件(OLED),采用空间电荷限制电流法估算了具有不同浓度FeCl3掺杂的CBP的空穴迁移率,并与OLED中常用的空穴传输材料N,N′-二苯基-N,N′-(1-萘基)-1,1′-联苯-4,4′-二胺(NPB)进行了比较研究。结果表明,FeCl3掺杂CBP可以极大地提高CBP薄膜的空穴迁移率,当FeCl3的浓度为12%时空穴迁移率最大,在电场强度为0.5MV/cm的条件下迁移率为4.5×10-5cm2/V·s,即使在零电场条件下迁移率依然高达2.2×10-5 cm2/V·s,近似为常用空穴传输材料NPB空穴迁移率的4倍。用CBP∶12%FeCl3做空穴传输层,制备了OLED器件,最大亮度为68468cd/m2,相对于采用NPB做空穴传输层的参比器件提高了97%,最大电流效率为31.28cd/A,比参比器件提高了23%。器件亮度和效率的提高归因于空穴传输性能的改善,使得器件中载流子的传输更为平衡,从而提高了激子形成的几率,且减少了激子-极化子之间的淬灭。     

镍基MOF电极材料物理超声改性及电化学性能

采用水热法合成了以4,4′-联苯二甲酸(BPDC)为配体的Ni-金属有机框架(MOF),利用低成本、无污染的物理超声法在不改变Ni-MOF晶体结构的前提下对其进行改性,使块状Ni-MOF表面产生孔隙,改善Ni-MOF表面微/纳米结构,提高其电化学性能。通过扫描电子显微镜(SEM)图、X射线衍射(XRD)谱、循环伏安(CV)曲线和恒电流充放电(GCD)曲线分析了改性前后Ni-MOF的微结构形貌和电化学性能。结果表明,经过超声处理后,Ni-MOF的比表面积从40.6 m^2·g^-1增加到65.8 m^2·g^-1,平均孔径从12 nm增加到22 nm。在0.5 A·g^-1电流密度下,超声处理后Ni-MOF电极比电容从420 F·g^-1增加到515 F·g^-1,提高了22.6%,电荷转移电阻明显降低,从25.11Ω降低到15.51Ω。因此,物理超声法可有效改善Ni-MOF表面微/纳米结构,提高其电化学性能。     

部分相干光光束并合的光束传输变换特性

运用维格纳(Wigner)分布函数(WDF)研究了高斯-谢尔模型(GSM)描述的部分相干光-光束并合的光束传输特性.推导出了并合光束的光束传输因子(M2因子)、峭度因子(K因子)以及光强分布的解析表达式.研究表明,并合光束的M2因子、K因子、光强分布和束宽依赖于总的空间相干度α,间距xd,束腰宽度ω0和GSM子光束数目N,如果子光束具有较大的α值,并合光束在远场更能达到较高的峰值光强和较窄的束宽.     

新型极化聚合物薄膜的制备及其光学特性研究

将新型有机NLO生色团分子GW-1-SF按一定比例掺入聚甲基丙烯酸甲酯(PMMA) 中,采用旋涂方法制备了聚合物复合薄膜.在100 ℃下对薄膜进行电晕极化,对极化前后的薄膜进行紫外/可见光吸收频谱分析和原子力显微镜分析.通过二次谐波法(SHG)测得其在1 064 nm波长下的二阶非线性系数d33为17.2 pm/V.详细讨论了材料两个二阶非线性系数d33和d13之间的关系,得出它们的比值d33/d13=3.45.     

基于Zn(Meq)_2为发光和主体材料OLEDs性能的研究

以2-甲基-8-羟基喹啉配体和ZnSO_4·7H_2O合成了有机金属配合物Zn(Meq)_2,并开展了材料的光电特性研究。当双层器件结构为ITO/NPB/Zn(Meq)_2/LiF/Al时,实现了绿光发射,EL峰位位于542 nm,最大亮度和效率分别为7 429 cd/m~2和1.80 cd/A。而当掺杂器件结构为ITO/NPB/Zn(Meq)_2:DCJTB/Alq_3/Li F/Al时,实现了红橙光发射,EL峰位位于580 nm,最大亮度和效率分别为6 075 cd/m~2和1.02 cd/A。结合器件结构和性能,讨论了相关工作机制。     

可溶性聚(2,5-二己氧基)对苯乙炔三阶非线性光学特性

报道了利用脱氯化氢反应制备可溶性聚(2,5二己氧基)对苯乙炔(PDHOPV),这种聚对苯乙炔(PPV)衍生物在波长450～550nm范围内具有强的光学吸收,最大吸收峰位于499nm处。采用简并四波混频(DFWM)技术对PDHOPV薄膜的非线性光学特性进行研究。结果表明:PDHOPV具有大的三阶非线性光学特性;激发波长为532nm的共振三阶非线性系数和1.064μm的非共振三阶非线性系数分别为9.6×10-10esu和2.1×10-11esu;电子共振增强有利于提高三阶非线性光学系数。     

新型含硒杂环红光聚芴电解质的电致发光器件制备和研究

利用新型的聚[9,9-二辛基芴-9,9-(双(3′-(N,N-二甲基)-N-乙基铵 溴-)丙基)芴-4,7-二噻吩-2-基-2,1,3-苯并硒二唑](PFNBr-DBSe)共扼聚电解质制备了聚合物发光二极管。这类共扼聚电解质可用乙醇等溶剂成膜,不仅可代替传统的甲苯等芳香性非极性溶剂,而且有利于制备溶液型的多层显示器件。文章研究了这类新型聚电解质的光致发光特性及发光二极管器件的电荧光特性。研究表明在紫外光照射或电激发下,窄带系的DBSe链段通过俘获激子能够实现有效的能量转移。聚电解质中DBSe的含量在5%以上,其器件具有电致发光峰值为700~740nm的饱和红光发射。所制聚电解质器件在用铝作电极时的电致发光效率比用钡作电极时要高。     

Raman spectroscopy applied to reveal polycrystalline grain structures and carrier transport properties of organic semiconductor films: Application to pentacene-based organic transistors

We have fabricated high performance polycrystalline pentacene-based thin-film transistors using several dielectrics with different surface properties, including inorganic oxide and polymeric materials. These materials provide excellent samples for the analysis of charge transport properties, particularly the impact of the grain boundary and the molecular structural quality within the grain on the efficient charge transport. The carrier transport in polycrystalline organic films with grain structures is often interpreted using the grain boundary model. Assuming a large amount of charges are trapped at the boundaries, the model neglects the microstructural quality inside a grain. According to joint experimental and theoretical Raman spectra and normal modes analysis on these pentacene films, we present a new observation that the microscopic hopping transport parameters, i.e., intermolecular interactions and reorganization energy, in polycrystalline films govern the carrier transport. An obvious, positive correlation is found between the mobility and the molecular vibrational characteristics, especially the intermolecular vibrational coupling energy, under all varieties of grain size morphology. MicroRaman mapping methodology reveals that the grain size of pentacene films should not be taken for granted in structural quality and efficient charge transport. The microstructural qualities inside the grain play an important role in efficient charge transport.     

High temperature carrier mobility as an intrinsic transport parameter of an organic semiconductor

The high temperature limit of hole mobility (μ_∞) in N,N′-diphenyl-N,N′-bis(1-naphthyl)(1,1′-biphenyl)-4,4′diamine (NPB) has been studied by time-of-flight technique. The effect of dopants on μ_∞ was also investigated. It was found that the μ_∞ is independent of the nature of dopants. The common μ_∞ can be applied to estimate the full temperature dependence of zero-field mobility (μ₀), if μ₀ at one temperature is known. We demonstrate this concept by predicting the room temperature μ₀ of NPB-doped with copper phthalocyanine (CuPc). The mobility prediction of CuPc-doped-NPB was then verified by the classic work of Hoesterey and Letson [D.C. Hoesterey, G.M. Letson, J. Phys. Chem. Solids 24 (1963) 1609].     

Nonlinear thermopower in bipolar semiconductor samples

The theory of the thermopower in bipolar semiconductor samples is developed taking into account the bending of the energy band near the semiconductor surface. The boundary conditions at the real metal- semiconductor junction and the nonequilibrium space charge appearing near the sample surface are taken into consideration. The model is constructed in the linear approximation in the temperature gradient, i.e., at a small deviation of the carrier density from equilibrium in the sample bulk. It is shown that the dependence of the thermopower on the temperature difference between the heater and cooler can become nonlinear at certain surface parameters and thicknesses of the semiconductor.     

The role of local potential minima on charge transport in thin organic semiconductor layers

We have performed a systematic study of dependence of time-resolved photocurrent on the point of charge excitation within the organic semiconductor channel formed by two coplanar metal electrodes. The results confirm that spatial variation of electric field between the electrodes crucially determines transport of photogenerated charge carriers through the organic layer. Time-of-flight measurements of photocurrent demonstrate that the transit time of photogenerated charge carrier packets drifting between the two electrodes decreases with increasing travelling distance. Such counterintuitive result cannot be reconciled with the spatial distribution of electric field between coplanar electrodes, alone. It is also in contrast to expected role of space-charge screening of external electric field. Supported by Monte Carlo simulations of hopping transport in disordered organic semiconductor layer, we submit that the space-charge screens the external electric field and captures slower charge carriers from the photogenerated charge carrier packet. The remaining faster carriers, exhibit velocity distribution with significantly higher mean value and shorter transit time.     

Characterisation of charge carrier transport in thin organic semiconductor layers by time-of-flight photocurrent measurements

The paper reviews recent advances in characterisation of charge carrier transport in organic semiconductor layers by time-of-flight photocurrent measurements, with the emphasis on the measurements of the samples with co-planar electrodes. These samples comprised an organic semiconductor layer whose thickness is on the order of a μm or less, and thus mimic the structures of organic thin film transistors. In the review we emphasise the importance of considering spatial variation of electric field in these, essentially two-dimensional structures, in interpretation of photocurrent transients. We review the experimental details of this type of measurements and give examples that demonstrate exceptional sensitivity of the method to minute concentration of electrically active defects in the organic semiconductors as well as the capability of probing charge transport along the channels of different mobility that reside in the same sample.     

A small-molecule organic semiconductor

The electrical conductivity and optical properties of bis-diethylaminokumarin have been investigated. The electrical conductivity of the compound exhibited three-dimensional hopping conduction in the temperature range 295–321 K. The compound shows a typical semiconductor property, and its semiconducting property results from delocalization of the π-electrons in the structure. To determine the optical band gap of the compound, an optical absorption study was made in the wavelength range 250–600 nm. The optical study revealed that the optical transition is the allowed indirect one. The electronic parameters, such as the electrical conductivity at room temperature σ₂₅, activation energy E, and optical band gap E_g of the compound are 1.46×10^?5 S/cm, 0.42 eV, and 2.46 eV, respectively. These values are in agreement with electronic parameters of organic semiconductors.     

Spin transport properties in double-barrier systems with diluted magnetic semiconductor doped layers

We have studied spin-polarized currents in resonant tunneling diodes containing diluted magnetic semiconductor layers with different geometries. The spin polarization effects on the resonant current are studied within Green's function formalism following the diagrammatic technique for non-equilibrium processes as proposed by Keldysh, using the one-band tight-binding modeling. The magnetic impurities can be located inside the well or the barrier layers of a diode sample. The resonant I×V curves are analyzed as a function of the magnetic potential strength induced by the magnetic ions.     

Barrier-limited transport in semiconductor devices

Current transport over a simple parabolic barrier is studied using the diffusion theory (dissipative transport) and the kinetic theory (ballistic transport). The solution of the diffusion equation for the barrier-limited case shows that the current density is inversely proportional to the width of the barrier. The solution of the kinetic theory, described by Euler's equation of classical fluid mechanics, gives a current density that is independent of the width of the energy barrier, and which is equal to 1.52 times the current density obtained from the thermionic emission theory. Euler's equation and the diffusion equation may be naturally combined into a single transport equation, and the current density derived from this equation shows the effects of both the ballistic and dissipative limits. The ballistic limits are of significance for the operation of the permeable base transistor and similar devices.     

Two formulations of semiconductor transport equations

Transport equations for semiconductors can be written with the diffusion term as qD₁?_n or as q?(D₂n), where D₁ and D₂ are diffusion coefficients. In a recent note in this journal the issues arising from this ambiguity were clarified and the possibility of a more general treatment, valid for arbitrary densities of states and current carriers, was announced. The details are given in this paper which includes magnetic field effects and covers also thermal conductivity, thermoelectric power and Soret coefficients in the two formulations. A special effort is made to develop a consistent macroscopic scheme of equations separately from their microscopic interpretations. A number of new equations and convenient connecting formulae between the two formulations are given; for example four general Einstein relations are found: for the electric and heat currents in the D₁- and the D₂-formulations.     

有机半导体激光器研究的新进展

近年来,有机半导体激光器已经成为一个新的研究热点。叙述了光泵浦有机半导体激光器的最新研究进展,对实现电泵浦（ 电注入） 有机半导体激光器也进行了评述。