Management of singlet and triplet excitons for efficient white organic light-emitting devices

Lighting accounts for approximately 22 per cent of the electricity consumed in buildings in the United States, with 40 per cent of that amount consumed by inefficient (approximately 15 lm W(-1)) incandescent lamps. This has generated increased interest in the use of white electroluminescent organic light-emitting devices, owing to their potential for significantly improved efficiency over incandescent sources combined with low-cost, high-throughput manufacturability. The most impressive characteristics of such devices reported to date have been achieved in all-phosphor-doped devices, which have the potential for 100 per cent internal quantum efficiency: the phosphorescent molecules harness the triplet excitons that constitute three-quarters of the bound electron-hole pairs that form during charge injection, and which (unlike the remaining singlet excitons) would otherwise recombine non-radiatively. Here we introduce a different device concept that exploits a blue fluorescent molecule in exchange for a phosphorescent dopant, in combination with green and red phosphor dopants, to yield high power efficiency and stable colour balance, while maintaining the potential for unity internal quantum efficiency. Two distinct modes of energy transfer within this device serve to channel nearly all of the triplet energy to the phosphorescent dopants, retaining the singlet energy exclusively on the blue fluorescent dopant. Additionally, eliminating the exchange energy loss to the blue fluorophore allows for roughly 20 per cent increased power efficiency compared to a fully phosphorescent device. Our device challenges incandescent sources by exhibiting total external quantum and power efficiencies that peak at 18.7 +/- 0.5 per cent and 37.6 +/- 0.6 lm W(-1), respectively, decreasing to 18.4 +/- 0.5 per cent and 23.8 +/- 0.5 lm W(-1) at a high luminance of 500 cd m(-2).     

Molecular-scale interface engineering for polymer light-emitting diodes

Achieving balanced electron-hole injection and perfect recombination of the charge carriers is central to the design of efficient polymer light-emitting diodes (LEDs). A number of approaches have focused on modification of the injection contacts, for example by incorporating an additional conducting-polymer layer at the indium-tin oxide (ITO) anode. Recently, the layer-by-layer polyelectrolyte deposition route has been developed for the fabrication of ultrathin polymer layers. Using this route, we previously incorporated ultrathin (<100 A) charge-injection interfacial layers in polymer LEDs. Here we show how molecular-scale engineering of these interlayers to form stepped and graded electronic profiles can lead to remarkably efficient single-layer polymer LEDs. These devices exhibit nearly balanced injection, near-perfect recombination, and greatly reduced pre-turn-on leakage currents. A green-emitting LED comprising a poly(p-phenylene vinylene) derivative sandwiched between a calcium cathode and the modified ITO anode yields an external forward efficiency of 6.0 per cent (estimated internal efficiency, 15-20 per cent) at a luminance of 1,600 candelas per m2 at 5 V.     

Formation cross-sections of singlet and triplet excitons in pi-conjugated polymers

Electroluminescence in organic light-emitting diodes arises from a charge-transfer reaction between the injected positive and negative charges by which they combine to form singlet excitons that subsequently decay radiatively. The quantum yield of this process (the number of photons generated per electron or hole injected) is often thought to have a statistical upper limit of 25 per cent. This is based on the assumption that the formation cross-section of singlet excitons, sigmaS, is approximately the same as that of any one of the three equivalent non-radiative triplet exciton states, sigmaT; that is, sigmaS/sigmaT approximately 1. However, recent experimental and theoretical work suggests that sigmaS/sigmaT may be greater than 1. Here we report direct measurements of sigmaS/sigmaT for a large number of pi-conjugated polymers and oligomers. We have found that there exists a strong systematic, but not monotonic, dependence of sigmaS/sigmaT on the optical gap of the organic materials. We present a detailed physical picture of the charge-transfer reaction for correlated pi-electrons, and quantify this process using exact valence bond calculations. The calculated sigmaS/sigmaT reproduces the experimentally observed trend. The calculations also show that the strong dependence of sigmaS/sigmaT on the optical gap is a signature of the discrete excitonic energy spectrum, in which higher energy excitonic levels participate in the charge recombination process.     

Efficient organic photovoltaic diodes based on doped pentacene

Recent work on solar cells based on interpenetrating polymer networks and solid-state dye-sensitized devices shows that efficient solar-energy conversion is possible using organic materials. Further, it has been demonstrated that the performance of photovoltaic devices based on small molecules can be effectively enhanced by doping the organic material with electron-accepting molecules. But as inorganic solar cells show much higher efficiencies, well above 15 per cent, the practical utility of organic-based cells will require their fabrication by lower-cost techniques, ideally on flexible substrates. Here we demonstrate efficiency enhancement by molecular doping in Schottky-type photovoltaic diodes based on pentacene--an organic semiconductor that has received much attention as a promising material for organic thin-film transistors, but relatively little attention for use in photovoltaic devices. The incorporation of the dopant improves the internal quantum efficiency by more than five orders of magnitude and yields an external energy conversion efficiency as high as 2.4 per cent for a standard solar spectrum. Thin-film devices based on doped pentacene therefore appear promising for the production of efficient 'plastic' solar cells.     

Efficient bulk heterojunction photovoltaic cells using small-molecular-weight organic thin films

The power conversion efficiency of small-molecular-weight and polymer organic photovoltaic cells has increased steadily over the past decade. This progress is chiefly attributable to the introduction of the donor-acceptor heterojunction that functions as a dissociation site for the strongly bound photogenerated excitons. Further progress was realized in polymer devices through use of blends of the donor and acceptor materials: phase separation during spin-coating leads to a bulk heterojunction that removes the exciton diffusion bottleneck by creating an interpenetrating network of the donor and acceptor materials. The realization of bulk heterojunctions using mixtures of vacuum-deposited small-molecular-weight materials has, on the other hand, posed elusive: phase separation induced by elevating the substrate temperature inevitably leads to a significant roughening of the film surface and to short-circuited devices. Here, we demonstrate that the use of a metal cap to confine the organic materials during annealing prevents the formation of a rough surface morphology while allowing for the formation of an interpenetrating donor-acceptor network. This method results in a power conversion efficiency 50 per cent higher than the best values reported for comparable bilayer devices, suggesting that this strained annealing process could allow for the formation of low-cost and high-efficiency thin film organic solar cells based on vacuum-deposited small-molecular-weight organic materials.     

2,6-二氨基-3,5-二硝基吡啶的合成与表征

2,6-二氨基-3,5-二硝基吡啶(DADNP)是一种非常重要的有机化合物,利用DADNP合成2,3,5,6-四氨基吡啶(TAP)是一个非常重要的有机反应,TAP是合成有机高分子化合物的一种重要单体,特别是在合成聚[2,5-二羟基-1,4-苯撑吡啶并双咪唑](PIPD)高分子化合物方面.DADNP的合成效果直接影响着TAP的纯度和产率以及PIPD高分子化合物的聚合工艺和产品性能.本文以大量的实验事实,提出了几种以2,6-二氨基吡啶(DAP)为原料合成DADNP的方法,总结出了几种切实可行的DADNP的合成方法,为高分子化合物PIPD的聚合工艺提供了强有力的单体保证和技术支撑.     

Efficient organic carbon burial in the Bengal fan sustained by the Himalayan erosional system

Continental erosion controls atmospheric carbon dioxide levels on geological timescales through silicate weathering, riverine transport and subsequent burial of organic carbon in oceanic sediments. The efficiency of organic carbon deposition in sedimentary basins is however limited by the organic carbon load capacity of the sediments and organic carbon oxidation in continental margins. At the global scale, previous studies have suggested that about 70 per cent of riverine organic carbon is returned to the atmosphere, such as in the Amazon basin. Here we present a comprehensive organic carbon budget for the Himalayan erosional system, including source rocks, river sediments and marine sediments buried in the Bengal fan. We show that organic carbon export is controlled by sediment properties, and that oxidative loss is negligible during transport and deposition to the ocean. Our results indicate that 70 to 85 per cent of the organic carbon is recent organic matter captured during transport, which serves as a net sink for atmospheric carbon dioxide. The amount of organic carbon deposited in the Bengal basin represents about 10 to 20 per cent of the total terrestrial organic carbon buried in oceanic sediments. High erosion rates in the Himalayas generate high sedimentation rates and low oxygen availability in the Bay of Bengal that sustain the observed extreme organic carbon burial efficiency. Active orogenic systems generate enhanced physical erosion and the resulting organic carbon burial buffers atmospheric carbon dioxide levels, thereby exerting a negative feedback on climate over geological timescales.     

Electroluminescent device with reversible switching between red and green emission

Research on new materials for organic electroluminescence has recently focused strongly on phosphorescent emitters, with the aim of increasing the emission efficiency and stability. Here we report the fabrication of a simple electroluminescent device, based on a semiconducting polymer combined with a phosphorescent complex, that shows fully reversible voltage-dependent switching between green and red light emission. The active material is made of a polyphenylenevinylene (PPV) derivative molecularly doped with a homogeneously dispersed dinuclear ruthenium complex, which fulfils the dual roles of triplet emitter and electron transfer mediator. At forward bias (+4 V), the excited state of the ruthenium compound is populated, and the characteristic red emission of the complex is observed. On reversing the bias (-4 V), the lowest excited singlet state of the polymer host is populated, with subsequent emission of green light. The mechanism for the formation of the excited state of the PPV derivative involves the ruthenium dinuclear complex in a stepwise electron transfer process that finally leads to efficient charge recombination reaction on the polymer.     

Nitride semiconductors free of electrostatic fields for efficient white light-emitting diodes

Compact solid-state lamps based on light-emitting diodes (LEDs) are of current technological interest as an alternative to conventional light bulbs. The brightest LEDs available so far emit red light and exhibit higher luminous efficiency than fluorescent lamps. If this luminous efficiency could be transferred to white LEDs, power consumption would be dramatically reduced, with great economic and ecological consequences. But the luminous efficiency of existing white LEDs is still very low, owing to the presence of electrostatic fields within the active layers. These fields are generated by the spontaneous and piezoelectric polarization along the [0001] axis of hexagonal group-III nitrides--the commonly used materials for light generation. Unfortunately, as this crystallographic orientation corresponds to the natural growth direction of these materials deposited on currently available substrates. Here we demonstrate that the epitaxial growth of GaN/(Al,Ga)N on tetragonal LiAlO2 in a non-polar direction allows the fabrication of structures free of electrostatic fields, resulting in an improved quantum efficiency. We expect that this approach will pave the way towards highly efficient white LEDs.     

对乙烯基苯磺酰氯与苯乙烯的原子转移自由基共聚合制备支化聚苯乙烯

以对乙烯基苯磺酰氯作为引发剂进行了苯乙烯的原子转移自由基聚合，由于对乙烯基苯磺酰氯同时含有可聚合的乙烯基和原子转移自由基聚合引发基团，因此可以得到支化结构的聚苯乙烯。用凝胶渗透色谱对不同对乙烯基苯磺酰氯浓度下所得聚合物的分子量及其分布进行了表征，发现所得聚合物的平均分子量明显大于按照每个对乙烯基苯磺酰氯分子产生一个聚合物链计算的理论分子量，并且分子量呈多峰分布。     

响应曲面法优化聚丙烯酰胺的反相乳液聚合

通过二次回归正交旋转组合实验设计,以单体质量分数、引发剂质量分数和反应温度为考察因素,用响应曲面法分析了这3个因素对产物聚丙烯酰胺特性粘数的影响.通过采用DPS数据处理软件,建立了聚合工艺的预测模型,预测最佳聚合工艺条件为:ω(单体)=40.0%,ω(引发剂)=0.2%,反应温度41.6℃,预测特性粘数为14.00 dL·g-1,验证实验所得的特性粘数为12.25 dL·g-1.两者结果相近,说明响应曲面法优化得到的聚丙烯酰胺反相乳液聚合模型是适用可行的.     

两类聚合物溶液的相变分析

讨论了两类聚合物溶液的相变,一类是单体相-溶胶相-凝胶相之间的相变;另一类是溶液中溶胶-凝胶之间的相变.结果表明,聚合物溶液体系相变的阶和相变点依赖于每个子系(单体或溶剂分子)的态的简并度以及子系间的有效相互作用;态的简并度的对称性和均匀性对相变的阶和临界点有明显的影响.     

油田污水配制用耐盐聚合物的制备与性能评价

大庆油田利用污水稀释聚合物溶液的区块比例超过80%,污水稀释聚合物溶液成为污水循环利用的主要途径。为解决污水条件下,普通聚合物用量高、不耐盐、应用性能差等制约聚驱开发提效的不利因素,通过优化设计聚合物分子结构,引入抗盐单体和刚性单体,采用多单体共聚后水解的合成工艺,制备了新型功能聚合物A。性能评价结果表明:相同分子量条件下,功能聚合物A的耐热稳定性、耐盐能力、抗剪切能力、注入能力及驱油效率等性能均优于部分水解聚丙烯酰胺。在相同浓度和注入体积条件下,功能聚合物A提高采收率11. 42%,较同分子量普通聚合物高3. 2%;在相同初始黏度和注入体积条件下,功能聚合物A采收率提高值较普通聚合物高1. 2%,且节约聚合物用量28%。功能聚合物A在油田污水中应用性能优于同分子量部分水解聚丙烯酰胺,可为聚合物驱开发降本增效提供新型高效驱油剂。     

膨胀型光缆阻水油膏用吸水剂的辐射合成

利用Co^60γ射线辐射引发聚合的方法以丙烯酸丁酯为改性组分合成亲油改性吸水剂,用于光缆用膨胀阻水油膏的制造.研究丙烯酸丁酯摩尔含量对其分散稳定性和吸水倍率的影响,确定组分配比：丙烯酸丁酯的摩尔分数为3 %,改性吸水剂在油膏中的质量浓度为5～10 g/.优化辐射工艺条件：辐射剂量率2.5 Gy/min,辐射剂量10 ～20 kGy.实验证明,改性吸水剂与基础油的相容性和分散稳定性明显提高,所制备的油膏性能指标满足要求.     

感光性可溶共轭聚合物聚对苯的合成

利用反应性高分子的取代反应,合成了含肉桂酸酯侧基的新型感光性共轭聚合物．首先用无水三氯化铁作氧化剂,利用氧化聚合法合成可溶性聚对苯——聚(1,4-二(4-氯丁氧基))苯,然后与肉桂酸钾进行高分子反应,合成了所设计的感光性共轭聚合物．采用FT-IR,UV-VIS,NMR,TGA和荧光光谱对聚合物的化学结构和性能进行了测试．聚合物在氯仿、THF、DMSO等溶剂中溶解性较好,在紫外光辐照下聚合物薄膜可进行交联反应。     

基于LED光电参数之间关系的光效计算

运用光色电综合分析仪测量了5种颜色LED(Light Emitting Diode)的光电参数,分析了光效与光电参数的关系,并研究了运用该关系测算光效的可能性。研究表明:LED电压、功率和电流均线性相关,随着电流的增加,LED光效线性下降,因此,电参数均可用来测算光效。主波长可以较好地评估绿色、黄色和蓝色LED的光效,红色和黄色LED光效可用峰值波长测算,用主波长或峰值波长测算白色LED光效精确度较低。色坐标与光效也成线性关系,且用于评估光效时精确度较主波长或峰值波长高。半高全宽也可用于测算光效,但用于白色和绿色LED时准确度较低。本研究对大型LED灯具光效的测算具有重要意义。     

单线态氧的光敏作用及其生物学意义

单线态氧是氧分子的一种特殊存在形式，具有很强的生物活性。本文介绍了单线态氧的的电子结构、产生方式、光敏作用和在有机合成中的应用，着重阐述了单线态氧的生物活性，即单线态氧对血液病的危害，单线态氧在癌诱发和衰老．游离基形成过程中的作用，单线态氧的吞噬作用及其它在生物体内的猝灭，展望了单线态氧的研究发展趋势。     

烯丙基缩水甘油醚与丙烯酸甲酯的活性聚合

研究了在咪唑基二硫代甲酸苄酯的存在下,热引发烯丙基缩水甘油醚与丙烯酸甲酯的活性自由基聚合反应.实验结果表明,共聚合反应具有良好的活性特征.聚合物分子量随单体转化率线性增长,分子量分布窄,ln([M]0/[M])与聚合反应时间呈线性关系.聚合物结构分析证明生成了含有环氧官能团的聚丙烯酸甲酯.烯丙基缩水甘油醚在聚合物中的含量随着转化率和它在单体中比例的增加而增加.不过当单体中烯丙基缩水甘油醚的比例增大时,反应速率降低.利用聚苯乙烯大分子控制剂,合成了含有环氧官能团的两嵌段共聚物,即聚苯乙烯-聚(烯丙基缩水甘油醚/丙烯酸甲酯)(PS-b-P(MA-co-AGE)).     

基于无机p型NiO缓冲层的钙钛矿发光二极管发光特性研究

【目的】研究如何提高溴基钙钛矿(CH3NH3PbBr3)发光二极管的发光亮度。【方法】通过在氧化铟锡(ITO)玻璃基底上引入无机p型NiO缓冲层与有机聚合物聚(3,4-亚乙二氧基噻吩)-聚(苯乙烯磺酸)(PEDOT∶PSS)形成有机/无机杂化空穴传输层,提高空穴注入效率,降低电子溢出。【结果】引入无机p型NiO缓冲层形成有机/无机杂化空穴传输层后,发光二极管的发光亮度提高了约1倍。【结论】该方法不仅可降低PEDOT∶PSS对ITO基底的腐蚀,还能显著提高空穴注入效率,提高发光二极管的发光亮度。     

基于能值分析的矿产资源效率研究

基于能值分析理论,建立了矿产资源效率能值分析方法,设计了矿产资源效率计量分析模型和指标;以辽宁省作为实证,对辽宁省矿产资源效率进行了能值评估及测算.结果表明,辽宁省矿产资源效率不断提高.从1990到2005年,矿产效率提高5.13倍.其中石油效率提高2.65倍,煤矿效率提高5.75倍,铁矿效率提高5.63倍.对辽宁省2010年到2050年应提高的矿产资源效率进行了预测.对测算结果进行了分析讨论并提出了提高矿产资源效率的对策与建议.