聚乙炔激子单线态和三线态的稳态性质与零磁场判据

在Su-Schrieffer-Heeger(SSH)模型基础上,计入弱电子关联的影响,研究聚乙炔单线态和三线态两类激子的行为.与单线态相比,三线态激子能级自旋简并丧失,能隙增大,电荷密度振荡局域分布以及自旋密度波产生,三线态激子吸收谱的相应特征峰发生~0.1 eV蓝移并且强度增加~40%.这些差异为区分两类激子提供了磁共振实验之外的判据.     

极化子比率变化对自旋注入有机半导体性质的影响

从自旋扩散方程和欧姆定律出发研究了铁磁层到有机半导体的自旋注入,得到了系统的电流自旋极化率。有机半导体中的载流子为自旋极化子和不带自旋的双极化子,极化子比率在有机半导体内随输运距离变化。通过计算发现匹配的铁磁和有机半导体电导率有利于自旋注入;通过调节界面电阻自旋相关性,电流自旋极化率可获得很大程度提高;极化子比率衰减速率对有机半导体电流自旋极化率具有非常重要的影响。     

单线态分裂的超快光谱学研究

有机分子中的单线态分裂过程能将单个光激发的单线态激子转化成两个三线态激子. 借助此载流子倍增效应, 太阳能电池可以更有效地利用太阳光谱中的高能光子, 进而突破单结太阳能电池效率的理论极限. 因此, 单线态分裂备受关注. 本文回顾学术界对单线态分裂物理图像的认识以及争议, 结合课题组近年来的一些结果, 重点总结此领域中运用瞬态光谱学方法取得的实验进展, 讨论有关多激子中间暗态机理的不同观点, 并介绍单线态分裂材料的发展以及器件应用.     

有机器件电流自旋极化放大性质研究

基于自旋扩散漂移方程,考虑到电场的影响及有机半导体中特殊的载流子电荷自旋关系, 对一个简单的T型结构有机自旋器件模型进行了理论研究,得出了此有机器件的电流自旋 极化放大率表达式.研究表明,器件中极化子比率、电场和电流密度都会影响器件的电流 自旋极化放大率,通过调节此有机器件的电场和极化子比率可以获得较大的电流自旋 极化放大率.     

OLEDs中的激子及其高效利用

有机发光二极管（OLEDs）是基于有机半导体的发光器件,由于具有自发光、响应速度快、发光颜色可调、轻薄、大面积柔性可弯曲等优点,被认为是新一代的显示和照明技术。OLEDs是通过注入的电子和空穴复合形成激子并辐射发光的过程,因此如何有效利用激子,特别是三线态激子,已经成为OLEDs材料和器件研究的重要课题。其中,如何把三线态激子能量转换成单线态激子,并最终实现100%激子的荧光发射更具有应用价值,最近几年这方面的研究已经取得了显著进展。本文从OLEDs的工作原理和发光过程出发,详细介绍了制备高效率荧光OLEDs的有效方法及其最新进展,并对未来发展方向进行了展望,为OLEDs材料和器件的研究提供重要参考。     

自旋极化度对GaAs量子阱中吸收饱和效应与载流子复合动力学的影响研究

本文研究了(001) GaAs量子阱薄膜中重空穴激子近共振抽运-探测的载流子自旋弛豫动力学, 发现载流子的自旋极化对传统的线偏振光吸收饱和效应和载流子复合动力学都有影响. 进一步的抽运流依赖的自旋弛豫和复合动力学研究表明, 自旋极化对线偏振光的吸收饱和效应的影响随抽运流降低而变弱. 在低激发流时, 自旋极化对线偏振吸收饱和效应的影响才可忽略. 然而, 又显现出自旋极化对复合动力学的影响. 分析表明复合动力学的自旋极化依赖性起源于重空穴激子形成浓度的自旋极化依赖性. 复合动力学的自旋极化依赖性表明自旋弛豫时间计算中所涉及的复合时间应该使用自旋极化载流子的复合时间. 基于二维质量作用定律的激子浓度计算表明, 库仑屏蔽效应对激子形成的影响在较低激发载流子浓度下可以忽略.     

自旋注入有机物的扩散理论

根据自旋注入半导体的相关理论， 考虑到有机体内可能同时含有带自旋的单极化子和不带自旋的双极化子两种载流子，从扩散 理论和欧姆定律出发，建立了自旋注入有机体的唯象模型.通过计算发现，适当选择铁磁层极化率或两层的电导率可以使得有机层内电流具有高的自旋极化.进一步研究了单极化子浓度等因素对注入电流极化的影响. 关键词： 自旋电子学 自旋注入 有机聚合物 极化子     

电场诱导聚合物分子取向对单线态和三线态激子形成截面的影响

通过对聚乙烯咔唑(PVK) 掺杂三(2-苯基吡啶)铱(Ir(ppy)₃)和4-二氰亚甲基-2-叔丁基-6-(1,1,7,7-四甲基久咯呢定基-9-烯基)-4H-吡喃(DCJTB)，PVK 掺杂DCJTB和PVK掺杂Ir(ppy)₃聚合物在成膜时高压电场作用下分子取向变化对单线态和三线态激子形成截面的研究，发现，随着成膜时电场的增强，单线态激子的形成截面在增加，而三线态激子的形成截面却减小. 关键词： 分子取向 激子形成截面 三线态 单线态     

铁磁/有机半导体/铁磁系统的电流自旋极化性质研究

根据有机半导体中的电流自旋极化注入和输运实验现象，理论上研究了铁磁/有机半导体/铁磁系统的电流自旋极化性质.考虑到有机半导体的具体特性，从自旋扩散理论和欧姆定律出发，得到了系统的电流自旋极化率.假设自旋极化子和不带自旋的双极化子为有机半导体中的载流子.通过计算发现，极化子为实现有机半导体中电流极化注入和输运的有效自旋载流子，即使它只占总载流子很少一部分.还进一步研究了自旋相关界面电阻和电导率匹配以及有机半导体长度等因素对系统电流自旋极化的影响. 关键词： 自旋电子学 自旋注入 有机半导体 极化子     

高分子中双激子态对外电场的线性响应

在外电场中,非简并基态共轭高分子中的双激子具有反向极化的奇异特性.利用响应函数求得高分子链的双激子态在任意频率下的动态极化率χ(ω),并通过求ω→0极限,给出双激子态的静态极化率χ,证实了χ确实为负值.并与激子态和基态作了比较,分析了分子负极化率的起因.考察了响应函数在低频时的行为,指出激子和双激子的激发浓度增大会导致材料折射率n(ω)向不同方向变化. 关键词：     

Theoretical study on spin-polarized injection of electrical currents into polymer semiconductors

Different from electrons and holes in traditional inorganic semiconductors, the charge carriers in polymer semiconductors are spin polarons and spinless bipolarons. In this paper, a theoretical model is presented to describe the spin-polarized injection of electrical currents from a ferromagnetic contact into a nonmagnetic polymer semiconductor. In this model, a new relation of conductivity to concentration polarization for polymer semiconductors is introduced based on a three-channel model to describe the spin-polarized injection of electrical currents under large electrical current densities. The calculated results of the model reveal the effects of the polaron ratio, the carrier concentration polarization, the interfacial conductance, the bulk conductivity of materials, and the electrical current density, etc. on the spin polarization of electrical currents. As conclusions, the large and matched bulk conductivity of materials, the small spin-dependent interfacial conductance, the thin polymer thickness and the large enough electrical current are critical factors for upgrading the spin polarization of electrical currents in polymer semiconductors. Particularly, when the polaron ratio in polymer semiconductors approaches the concentration polarization of the ferromagnetic contact, a modest concentration polarization is sufficient for achieving a nearly complete spin-polarized injection of electrical currents.     

Transparent manganite films as hole injectors for organic light emitting diodes

Organic light-emitting diodes (OLEDs) are nowadays one of the most attractive devices based on organic semiconductors due to their successful application in the display technology. Electroluminescence in OLEDs is mainly governed by the fluorescence from excited singlet states, which have large transition probabilities providing the major radiative pathway. The “forbidden” triplet state emission can be activated by increasing spin–orbit coupling via dye doping. The singlet–triplet exciton formation statistics is usually given by 1:3 partition due to the quantum constrains.

Injection of carriers with finite spin polarisation should influence and modify the recombination statistics and can be used for tuning of the device efficiency. In this context, the development of a new class of electrodes able to guarantee both efficient charge and spin injection becomes of paramount importance. We show that strongly spin polarised colossal magnetoresistance manganite La_0.7Sr_0.3MnO₃ (LSMO) can successfully substitute conventional ITO electrodes in OLEDs. Highly transparent, metallic and ferromagnetic LSMO layers were used in combination with standard Al and spin polarised Co top electrodes. Electrical and optical characterisations of the OLEDs with spin polarised electrodes indicate the applicability of the new manganite electrodes for organic light-emitting devices.     

高效率的有机电致发光器件

有机电致发光器件 (OL EDs)的发光机理包括电子和空穴从电极的注入、激子的形成及复合发光 ,其中 ,空穴和电子的注入平衡是非常重要的。为了平衡载流子的注入以得到高效率和稳定性好的器件 ,人们不仅使用了电子注入更为有效的 L i F/ Al[1] 和 Cs F/ Al[2 ] 等复合电极 ,同时也使用了空穴缓冲层 ,如 S.A.Van Slyke等 [3]在ITO和 NPB之间使用 Cu Pc,使得器件的稳定性得到了明显的提高 ;A.Gyoutoku等[4 ] 用碳膜使器件的半寿命超过 3 5 0 0小时 ;最近 ,Y.Kurosaka等 [5]和 Z.B.Deng[6 ]分别在 ITO和空穴传输层之间插入一薄层 Al…     

迁移率对单层有机发光器件中电场与载流子分布的影响

有机发光器件的宏观特性与有机层中的电场和载流子浓度分布密切相关。建立的有机电致发光器件模型是由两个金属电极中间夹一层有机发光薄膜材料组成的单层器件,金属与有机发光层之间为欧姆接触。模型以载流子运动的扩散-漂移理论为基础,利用数值方法研究了有机发光层中双极载流子注入时的电势、电场、载流子浓度和复合密度分布。分析结果表明:当两种载流子的迁移率相同时,电场强度、载流子浓度、复合密度的分布呈对称形式。而当电子和空穴的迁移率μn和μp相差比较大时,高迁移率的载流子不仅仅分布在注入端附近而且还有一小部分能够传输到另一端,而低迁移率的载流子只分布在其注入端附近;当μn、μp的大小相差不大时,载流子传输情况就介于两者之间。当μn/μp的比值变化时,电场强度的极大值向载流子迁移率小的注入端偏移。     

Ir(ppy)3掺杂PVK体系发光特性的研究

对常温下磷光染料Ir(ppy)3掺杂PVK薄膜的光致发光(PL)和电致发光(EL)特性进行了研究。器件结构为ITO/PEDOT:PSS/PVK:Ir(ppy)3/BCP/Alq3/Al。实验发现随磷光材料掺杂浓度的不同,器件的发光性能发生变化。当浓度适宜时,主体材料PVK的发光很弱,主要为Ir(ppy)3的磷光发射。通过L-I-V特性曲线的比较,掺杂浓度为5%的光电性能最好,说明器件在掺杂浓度为5%时效果最佳。     

Long-lived two-dimensional triplet magnetoexcitons in a Hall insulator

An experimental technique is developed to perform photoexcitation of an ensemble of translationinvariant triplet excitons, to manipulate this ensemble, and to detect the properties of its components. In particular, the influence of temperature on the radiationless decay during the relaxation of an exciton spin into the ground state of a Hall insulator at a filling factor ν = 2 is studied. The generation of photoexcited electrons and holes is controlled using photoinduced resonance reflection spectra, which makes it possible to estimate the density of light-generated electron–hole pairs and to independently control the self-consistent generation of electrons at the first Landau level and holes (vacancies) at the ground (zero) cyclotron electronic level. The existence of triplet excitons is established from inelastic light scattering spectra, which are used to determine the singlet–triplet exciton splitting. The lifetimes of triplet excitons, which are closely related to the relaxation time of an electron spin, are extremely long: they reach 100 μs in perfect GaAs/AlGaAs heterostructures with a high mobility of two-dimensional electrons at low temperatures. These long spin relaxation times are qualitatively explained, and the expected collective behavior of high-density triplet magnetoexcitons at sufficiently low temperatures, which is related to their Bose nature, is discussed.     

Ir(PPY)3掺杂PVK的电致发光机理

近几年来发展起来的电致磷光(electrophosphorescence)是有机发光二极管(OLED)研究的新生长点。对电致磷光发光机理的研究随即得到了人们普遍的关注。比较了不同正向偏压条件下Ir(PPY)₃掺杂聚乙烯基咔唑(PVK)的光致发光(PL)和电致发光(EL)光谱。研究结果显示在电场和注入电流的共同作用下,PL光谱中基质PVK发光的相对强度并没有发生显著的变化。电场或注入载流子不会影响PVK向Ir(PPY)₃的能量传递。磷光掺杂聚合物EL主要是由于载流子在掺杂磷光分子上的直接复合,而不是由基质向磷光掺杂分子的能量传递。     

Spin-Polarized Carriers Injection from Ferromagnetic Metal into Organic Semiconductor

Charge carriers in organic semiconductor are different from that oftraditional inorganic semiconductor. Based on three-current model,considering electrical field effect, we present a theoretical model todiscuss spin-polarized injection from ferromagnetic electrode into organicsemiconductor by analyzing electrochemical potential both in ferromagneticelectrode and organic semiconductors. The calculated result of this modelshows effects of electrode's spin polarization, equilibrium value ofpolarons ratio, interfacial conductance, bulk conductivity of materials andelectrical field. It is found that we could get decent spin polarizationwith common ferromagnetic electrode by increasing equilibrium value ofpolarons ratio. We also find that large and matched bulk conductivity oforganic semiconductor and electrode, small spin-dependent interfacialconductance, and enough large electrical field are critical factors forincreasing spin polarization.     

Spin-polarized injection into a p-type GaAs layer from a Co2 MnAl injector

Electric luminescence and its circular polarization in a Co2 MnAl injector-based light emitting diode (LED) has been detected at the transition of e-A0 C , where injected spin-polarized electrons recombine with bound holes at carbon acceptors. A spin polarization degree of 24.6% is obtained at 77 K after spin-polarized electrons traverse a distance of 300 nm before they recombine with holes bound at neutral carbon acceptors in a p + -GaAs layer. The large volume of the p + -GaAs layer can facilitate the detection of weak electric luminescence (EL) from e-A 0C emission without being quenched at higher bias as in quantum wells. Moreover, unlike the interband electric luminescence in the p+ -GaAs layer, where the spin polarization of injected electrons is destroyed by a very effective electron-hole exchange scattering (BAP mechanism), the spin polarization of injected electrons seems to survive during their recombination with holes bound at carbon acceptors.