Effects of coupling lens on optical refrigeration of semiconductors

Optical refrigeration of semiconductors is encountering efficiency difficulties caused by nonradiative recombination and luminescence trapping. A commonly used approach for enhancing luminescence efficiency of a semiconductor device is coupling a lens with the device. We quantitatively study the effects of a coupling lens on optical refrigeration based on rate equations and photon recycling, and calculated cooling efficiencies of different coupling mechanisms and of different lens materials. A GaAs/GaInP heterostructure coupled with a homo-epitaxial GaInP hemispherical lens is recommended.

高迁移率噻吩杂化共轭齐聚物的合成与表征

并苯类化合物和噻吩齐聚物是目前研究最广泛的两类p型高迁移率有机半导体材料，晶态下强分子间电子相互作用的特点使它们具有优异的电荷传输性质，作为电荷传输层制备的有机薄膜晶体管（OTFT）的器件性能已经可以和非晶硅器件（α- Si:H）相比拟（0.1~1.0 cm2/V.s）。但是，由于这两类材料具有较窄的能隙和较高的最高被占分子轨道（HOMO） 能级，容易与空气中的水、氧发生反应，而且并苯类化合物对光也非常敏感，因此它们的器件性能在空气中衰减很快。可以说，如何设计与合成兼具高迁移率和优异稳定性的OTFT材料依然是目前有机光电子研究领域面临的挑战之一。 在本论文中，我们采用较稳定的芳香基团和噻吩单元构造了三个系列杂化共轭齐聚物，通过改变芳香基团结构和引入方式，对共轭齐聚物的HOMO能级做了有效的调节，不仅提高了分子的热稳定性和化学稳定性，而且使分子的HOMO能级与金电极功函相匹配，有利于电荷的注入，获得了稳定的高迁移率有机半导体材料。 1、设计并合成了一系列含不同苯类（苯、联苯、芴和菲）中心单元的噻吩类共轭齐聚物，表征了它们基本的光谱、电化学和热行为，并作为传输层用于顶电极结构的OTFT，获得了较高的场致迁移率（（1－6.7）×10-2 cm2/V.s）。引入平面刚性芳香基团有利于获得稳定的高迁移率材料。噻吩/菲杂化共轭齐聚物，即2,7二（5'正己基2,2'二噻吩5）菲（DH-TTPhTT）综合性能最佳，与在相同条件下制备的DH6T具有相当的场致迁移率（μFET = 0.065 cm2/V.s）。 2、设计并合成了一系列含菲共轭齐聚物，研究了它们的基本物理和化学性质。[2,2';7',2''] 三联菲（Ph3）可通过真空蒸镀形成高度有序的薄膜，其OTFT μFET达0.01 cm2/V.s。但是，由于其HOMO能级太低，导致器件阈值电压很高，很难进一步优化器件性能。因此，为了调节分子的HOMO能级，合成了2 ,5二（2菲基） [3,2-b]并二噻吩（PhTT）和5,5'二(2菲基) 2,2'二噻吩（PhT2）两个含噻吩化合物，成功的应用于顶电极结构的OTFT，使器件性能大幅提高。其中PhT2的μFET > 0.1 cm2/V.s； Ion/Ioff > 1×105。更重要的是，器件在空气、自然光条件下保存一个月后，μFET 、Ion/Ioff和阈值电压三个性能指标都基本没有变化，说明PhT2是目前最好的OTFT材料之一。 3、设计并合成了六个萘和硫茚封端的噻吩齐聚物，研究了它们的基本物理和化学性质。为了对分子结构—堆积方式—器件性能的关系有所认识，解析了5,5'二(2萘基) 2,2'二噻吩（NaT2），5,5''二(2萘基) 2,2':5',2''三噻吩(NaT3)，5,5'二(2硫茚基) 2,2'二噻吩（TNT2）和5,5''二(2硫茚基) 2,2':5',2''三噻吩(TNT3) 的单晶结构。所有六个化合物均可形成高度有序的多晶薄膜，而且薄膜有序性随噻吩单元数的增加而提高。取决于分子长度和端基结构，它们的μFET介于0.01－0.39 cm2/V.s。和TNTn系列分子(n = 2-4)相比，NaTn系列齐聚物(n = 2-4)具有更好的器件性能。齐聚物5,5'''二(2萘基) 2,2':5',2'':5'',2'''四噻吩（NaT4）具有最好的器件性能，其场致迁移率为0.39 cm2/V.s；VT = -5 V； Ion/Ioff > 1×105，是目前性能最好的OTFT材料之一。

端基官能化共轭齐聚物的设计与合成

和共轭聚合物相比，单分散共轭齐聚物具有结构确定、易提纯等优点，不仅是建立共轭体系结构与性能关系的最佳模型，而且是一类高纯度光电子材料，还是构造具有规整结构嵌段共聚物和超分子体系的理想构造单元。鉴于基于芴单元的共轭齐聚物与聚合物具有优异的光电性能，引入不同端基能够有效调节共轭齐聚物的性能，本论文以端基官能化齐聚芴为研究对象，设计与合成了具有不同端基结构的系列单分散齐聚芴，研究了它们基本的物理化学性质，主要成果与创新点如下： 1、利用Horner-Wadsworth-Emmons反应、Wittig反应和Heck偶联反应，交替引入极性、非极性反应端基，成功解决了发散法合成较长单分散共轭齐聚物过程中产物难以提纯的技术问题，合成了系列芴撑乙烯撑共轭齐聚物。其中，最长的齐聚物含11个芴单元，光谱外推得到的有效共轭长度可达19个重复单元。DSC和偏光显微镜研究表明，芴单元数大于5的齐聚物可形成向列型液晶相。含7个芴单元以上的齐聚物可用于制备有机发光二极管，含11个芴单元的齐聚物电致发光效率是相应聚合物的5倍。 2、通过Hagigara-Sonogashira偶联、Diels-Alder环加成等反应合成了一系列端基为刚性的苯乙炔基和五苯基苯的单分散齐聚芴。但典型Scholl反应条件不能实现完全氧化脱氢，获得六苯并晕苯封端的齐聚芴。光谱研究表明苯乙炔基的引入导致吸收光谱和荧光光谱有1-2 nm的红移。五苯基苯结构的引入能显著提高齐聚芴的Tg，从而提高齐聚物的形态稳定性。 3、利用Yamamoto反应，采用端基溴代的齐聚芴大分子单体聚合结合制备色谱分离，成功地制备了分子量超过20000 Da的单分散共轭聚合物，说明大分子单体聚合结合制备色谱分离制备单分散共轭聚合物是可行的。 4、通过Horner-Wadsworth-Emmons反应合成一系列端基为三苯胺乙烯撑的单分散齐聚芴，其中，最长的齐聚物含9个芴单元。光谱研究表明，随芴单元数的增加，两个三苯胺乙烯撑端基间共轭作用显著减弱，最大吸收波长蓝移；当芴的单元数≥3时，最大发射波长均位于450 nm，和聚芴和齐聚芴相比，这类共轭齐聚物的蓝光发光峰位更佳。电化学研究表明三苯胺乙烯撑单元的氧化还原过程不受齐聚芴单元长度的影响，该封端齐聚芴的HOMO能级主要是由三苯胺乙烯撑单元决定。 关键词：端基官能化，齐聚芴，单分散共轭聚合物

有机异质结晶体管中功能与形貌关系的研究

有机薄膜晶体管由于具有低成本、易于柔性基底兼容、可以大面积制作等优点，已经在有源平板显示、低端电子产品以及传感器等方面显示出了极大的应用潜力。由于有机异质结具有一些与无机异质结不同的特性，而基于有机异质结的电子器件也显示出越来越受到人们的关注。因此，本论文的工作主要集中在有机异质结薄膜晶体管的功能与薄膜形貌的研究上。 1． 我们首先研究了BP2T/F16CuPc异质结的特征（第二章）。在BP2T/F16CuPc异质结界面处，BP2T的能级向上弯曲，F16CuPc的能级向下弯曲，费米能级穿越F16CuPc的LUMO。并且在其异质结界面处，存在载流子的累积，其中空穴累积在BP2T中，累积厚度大约为10 nm，电子累积在F16CuPc中，累积厚度大约为20 nm。 2． 我们利用BP2T/F16CuPc异质结的特征，通过改变BP2T的厚度，在BP2T/F16CuPc有机异质结薄膜晶体管中实现了晶体管的三种工作模式（第三章）：n沟道、双极型和p沟道。在n沟道模式下，电子迁移率随着厚度的增加而增大；在双极型模式下，电子和空穴的迁移率先随着BP2T厚度增加而增加，当BP2T的厚度超过5 nm 时，电子和空穴的迁移率分别达到最大值，随着BP2T厚度的继续增加，电子和空穴的迁移率就开始下降；在p沟道模式下，空穴的迁移率不在随着BP2T厚度的变化而变化。通过对BP2T薄膜进行原子力表征，我们发现这些规律是与BP2T薄膜的表面形貌密切相关的，并给出了载流子累积的示意图。 3． 根据BP2T/F16CuPc有机异质结薄膜晶体管在三种工作模式中所具有的规律，将其双极型的工作模式推广到金属酞菁体系、菲体系、硫茚体系以及萘体系与F16CuPc的异质结材料对中，并分别从第一半导体的生长方式、 分子长度以及迁移率等方面对实现高性能的双极型传输进行了讨论（第四章）；在BP2T/F16CuPc有机异质结薄膜晶体管中将单极型电子的迁移率提高到了0.06 cm2/V•s，将双极型电子的迁移率提高到了0.1 cm2/V•s，并且观察到了F16CuPc在BP2T上具有弱外延生长；在NaT4/F16CuPc有机异质结薄膜晶体管中通过设计新的器件构型，实现了高迁移率、高开关比的p型常开型工作模式。

高分子空穴传输材料的合成与性能研究

本论文以改善有机／高分子电致发光器件的载流子注入与传输平衡为目的，以具有良好成膜性、热稳定性及氧化还原性的氮硫共扼聚合物为母体，通过在氮上引入不同的侧基来研究所得聚合物的空穴传输性能，发光性能及其在电致发光器件中佩的应用。1．设计与合成出一系列不同链长的烷基取代的氮硫共扼聚合物，所得聚合物具有规整的结构，高的分子量，可溶于常见的有机溶剂且具有良好的成膜性。电化学研究表明，它们具有良好的氧化还原可逆性及稳定性，其HOMO值在5.02一5.16eV之间，与阳极ITO具有较好的匹配，说明它们有着良好的空穴注入性能。通过对“hole-only"器件（ITO/PPSA-R/C u )的研究表明随着烷基侧链的增长，所得聚合物的空穴传输能力逐渐下降。双层器件(TO/PPSA-R/Alq3几佩F/AI）研究结果表明与传统的高分子空穴传输材料聚乙烯咔叫含(PVK)相比，器件的启动电压降低，发光效率明显提高，说明烷基取代氮硫共扼聚合物具有优良的空穴传输性能。2.设计与合成出侧链悬挂有三芳胺类空穴传输小分子的氮硫共辆单体，在强酸体系下聚合后，通过核磁表征发现由于醚键断裂导致部分三芳1}5}小分子脱落，聚合物中三芳胺小分子含量降低。电化学研究表明它们具有良好的氧化还原可逆性，其HOMO值在-5.18eV左右，大于未引入二芳服时的氮硫共扼聚合物。双层器件(ITO/PPSA-TPA/Alq3/LiF/Al)研究结果表明，与未引入三芳l}}C的氮硫共扼聚合物相比，器件的启动电压升高，发光效率降低。3.设计与合成出侧链悬挂有高荧光效率的蓝色发光二苯葱小分子的氮硫单体，并通过其与可合成出高性能的空穴传输材料一的乙基取代的氮硫单体以不同比例共聚获得一系列新型的主链传输空穴而侧链发光的聚合物。它们具有高的热稳定性，良好的溶解性及成膜性，电化学研究表明它们具有良好的氧化还原可逆 性及低的起始氧化电位。通过对其发光性质的研究，我们发现在溶液荧光光谱中短波长的发射归结于二苯葱单体的发射，而长波长的发射则归结于分子内或分子间受激分子的发射；在固体膜的荧光光谱中，主要表现为激基缔合物发光，并随着二苯葱基元含量的减少光致发光亮度增加，且发光蓝移。4.设计与合成出含有N一烷基咔吟或N一芳基咔畔和不同发光中心的小分子发光材料，我们发现含葱环的发光小分子发光颜色向长波移动，含联苯结构的发光小分子的发光颜色则向短波移动。电化学研究表明，11卜畔的存在提高了发光小分子的空穴传输性能。通过将含有电子传输层的发光小分子双层器件与单层器件对比，我们发现双层器件的各项性能远高于单层器件，进一步说明了发光小分子传输性能的改善。

Preparation and characteristics of nonflammable polyimide materials

The thermal and flame-retardant properties of homo- and copolyimides were evaluated. Those containing sulfone linkages in the backbone were found to be more flame retardant. Both properties were dependent on the composition. A polyimide/silica nanocomposite was obtained through sol-gel processing. The effects of the addition of silica an the dispersion, interfacial adhesion, fire resistance, mechanical properties, and thermal stability of the composites were investigated. SEM analysis showed a good dispersion of silica with a diameter of 50-300 nm in the organic matrices. The addition of silica increased the fire retardancy and mechanical properties of the composites. (C) 2000 John Wiley & Sons, Inc.

Length dependence of electron conduction for oligo(1,4-phenylene ethynylene)s: A conductive probe-atomic force microscopy investigation

The dependence of electron conduction of oligo(1,4-phenylene ethynylene)s (OPEs) on length, terminal group, and main chain structure was examined by conductive probe-atomic force microscopy (CP-AFM) via a metal substrate-molecular wire monolayer-conductive probe junction. The electron transport in the molecular junction was a highest occupied molecule orbital (HOMO)-mediated process following a coherent, non-resonant tunneling mechanism represented by the Simmons equation.

Solution-Processable Carbazole-Based Conjugated Dendritic Hosts for Power-Efficient Blue-Electrophosphorescent Devices

A novel class of hosts suitable for solution processing has been developed based on a conjugated dendritic scaffold. By increasing the dendron generation, the highest occupied molecular orbital (HOMO) energy level can be tuned to facilitate hole injection, while the triplet energy remains at a high level, sufficient to host high-energy-triplet emitters. A power-efficient blue-electrophosphorescent device based on H2 (see figure) is presented.

Colorimetric recognition of the coralyne-poly(dA) interaction using unmodified gold nanoparticle probes, and further detection of coralyne based upon this recognition system

Among the functional nucleic acids studied, adenine-rich nucleic acids have attracted attention due to their critical roles in many biological processes and self-assembly-based nanomaterials, especially deoxyribonucleic acids (abbreviated as poly(dA)). Therefore the ligands binding to poly(dA) might serve as potential therapeutic agents. Coralyne, a kind of planar alkaloid, has been firstly found that it could bind strongly to poly(dA). This work herein reports an approach for visual sensing of the coralyne-poly(dA) interaction. This method was based on the coralyne inducing poly(dA) into the homo-adenine DNA duplex and the difference in electrostatic affinity between single-stranded DNA and double-stranded DNA with gold nanoparticles (GNPs). Furthermore, we applied the recognition process of the interaction between coralyne and poly(dA) into specific coralyne detection with the assistance of certain software (such as Photoshop). A linear response from 0 to 728 nM was obtained for coralyne, and a detection limit of 91 nM was achieved.

Rational Design, Synthesis, and Optical Properties of Film-Forming, Near-Infrared Absorbing, and Fluorescent Chiromophores with Multidonors and Large Heterocyclic Acceptors

A new series of film-forming, low-bandgap chromophores (1a,b and 2a,b) were rationally designed with aid of a computational study., and then synthesized and characterized. To realize absorption and emission above the 1000 nm wavelength, the molecular design focuses on lowering the LUMO level by fusing common heterocyclic units into a large conjugated core that acts an electron acceptor and increasing the charge transfer by attaching the multiple electron-donating groups at the appropriate positions of the acceptor core. The chromophores have bandgap levels of 1.27-0.71 eV, and accordingly absorb at 746-1003 nm and emit at 1035-1290 nm in solution. By design, the relatively high molecular weight (up to 2400 g mol(-1)) and non-coplanar structure allow these near-infrared (NIR) chromophores to be readily spin-coated as uniform thin films and doped with other organic semiconductors for potential device applications. Doping with [6,6]-phenyl-C-61 butyric acid methyl ester leads to a red shift in the absorption on]), for la and 2a. An interesting NIR electrochromism was found for 2a, with absorption being turned on at 1034 nm when electrochemically switched (at 1000 mV) from its neutral state to a radical cation state. Furthermore, a large Stokes shift (256-318 nm) is also unique for this multidonor-acceptor type of chromophore.

Diarylmethylene-bridged 4,4 '-(bis(9-carbazolyl))biphenyl: morphological stable host material for highly efficient electrophosphorescence

novel compound (BCBP) based on the modification of a well-known host material 4,4'-(bis(9-carbazolyl))biphenyl (CBP) through arylmethylene bridge linkage was synthesized, and fully characterized. Its thermal, electrochemical, electronic absorption and photoluminescent properties were studied. A high glass transition temperature (T-g) of 173 degrees C is observed for BCBP due to the introduction of the bridged structure, remarkably contrasting with a low T-g of 62 degrees C for CBP. Furthermore, the bridged structure enhances the conjugation and raises the HOMO energy, thus facilitating hole-injection and leading to a low turn-on voltage in an electroluminescent device. With the device structure of ITO/MoO3/NPB/Ir complex: BCBP/BCP/Alq(3)/LiF/Al, maximum power efficiencies of 41.3 lm/W and 6.3 lm/W for green- and blue-emitting OLED were achieved, respectively.

Copolymerization of ethylene with norbornene catalyzed by cationic rare earth metal fluorenyl functionalized N-heterocyclic carbene complexes

Rare earth metal bis(alkyl) complexes attached by fluorenyl modified N-heterocyclic carbene (NHC) (Flu-NHC)Ln(CH2SiMe3)(2) (Flu-NHC = (C13H8CH2CH2(NCHCCHN)C6H2Me3-2,4,6); Ln = Sc (2a); Y (2b); Ho (2c); Lu (2d)), ((tBu)Flu-NHC)Ln(CH2SiMe3)(2) ((tBu)Flu-NHC = 2,7-(Bu2C13H6CH2CH2)-Bu-t(NCHCCHN)C6H2Me3-2,4,6; Ln = Sc (1a); Lu (1d)) and attached by indenyl modified N-heterocyclic carbene (Ind-NHC)Ln(CH2SiMe3)(2) (Ind-NHC = C9H6CH2CH2(NCHCCHN)C6H2Me3-2,4,6; Ln = Sc (3a); Lu (3d)), under the activation of (AlBu3)-Bu-i and [Ph3C][B(C6F5)(4)], showed varied catalytic activities toward homo- and copolymerization of ethylene and norbornene. Among which the scandium complexes, in spite of ligand type, exhibited medium to high catalytic activity for ethylene polymerization (10(5) g mol(Sc)(-1) h(-1) atm(-1)), but all were almost inert to norbornene polymerization. Remarkably, higher activity was found for the copolymerization of ethylene and norbornene when using Sc based catalytic systems, which reached up to 5 x 10(6) g mol(Sc)(-1) h(-1) atm(-1) with 2a. The composition of the isolated copolymer was varying from random to alternating according to the feed ratio of the two monomers (r(E) = 4.1, r(NB) = 0.013).

Solvent effects on spectrophotometric titrations and vibrational spectroscopy of 5,10,15-triphenyl-20-(4-hydroxyphenyl)porphyrin in aqueoius DMF

The spectrophotometric titration by sodium hydroxide of 5,10,15-triphenyl-20-(4-hydroxyphenyl)porphyrin ((OH)(1)PH2) is studied as a function of solvent composition of DMF-H2O binary solvent mixture ([OH-] = 0.04 M). Combining the structure changes of the porphyrin and the "four orbital" model of Gouterman, many features of the optical spectra of this deprotonated para-hydroxy-substituted tetraphenylporphyrin in different composition of binary solvent mixtures can be rationalized. In highly aqueous solvents, the changes of the titration curves are shown to be mainly due to hydrogen-bonding of the oxygen of the phenoxide anion group by the hydroxylic solvent, Which decreases the energy of the phenoxide anion pi orbital. Thus the phenoxide anion pi orbital cannot cross over the porphyrin Tr orbital being a different HOMO. However, its energy is close to that of the porphyrin pi orbitals. As a result, in the visible region, no charge-transfer band is observed, while in the visible-near region, the Soret peak split into two components. In nonaqueous solvents, the changes are mainly attributed to further deprotonation of pyrrolic-Hs of (OH) 1PH2 by NaOH and coordination with two sodium ions to form the sodium complex of (OH) 1PH2, which turns hyperporphyrin spectra of deprotonated of phenolic-H of (OH)(1)PH2 into three-banded spectra of regular metalloporphyrin.

Photoluminescence and electroluminescence properties of a samarium complex Sm(TTA)(3)phen

The photoluminescence (PL) and electroluminescence (EL) properties of a samarium complex Sm(TTA)(3)phen (TTA = 2-thenoyltri-fluoroacetonate, phen = 1, 10-phenanthroline) were investigated. The results show that Sm(TTA)3phen could be used as promising luminescent and electron transporting material in the electroluminescent devices. The difference between PL and EL spectra was noticed and discussed. Besides, it is noteworthy that the choice of the hole transporting layer (HTL) showed significant effect on the device performance, which was explained by the low-lying highest occupied molecular orbit (HOMO) level of Sm(TTA)3phen and the different hole injection barrier at the HTL/EML (emitting material layer) interface.

Syntheses and ethylene polymerization behavior of supported salicylaldimine-based neutral nickel(II) catalysts

Two novel salicylaldimine-based neutral nickel(II) complexes, [(2,6-iPr(2)C(6)H(3))NCH(2-ArC6H3O)]Ni(PPh3)Ph (6, Ar = 2-(OH)C6H4; 8, Ar = 2-OH-3-(2,6-iPr(2)C(6)H(3)NCH)C6H3), have been synthesized, and their structures have also been confirmed by X-ray crystallography, elemental analysis, and H-1 and C-13 NMR spectra. An important structural feature of the two complexes is the free hydroxyl group, which allows them to react with silica pretreated with trimethylaluminum under immobilization by the formation of a covalent bond between the neutral nickel(II) complex and the pretreated silica. As active single-component catalysts, the two complexes exhibited high catalytic activities up to 1.14 and 1.47 x 10(6) g PE/mol(Ni)center dot h for ethylene polymerization, respectively, and yielded branched polymers. Requiring no cocatalyst, the two supported catalysts also showed relatively high activities up to 4.0 x 10(5) g PE/mol(Ni)center dot h and produced polyethylenes with high weight-average molecular weights of up to 120 kg/mol and a moderate degree of branching (ca. 13-26 branches per 1000 carbon atoms).