基于LiF/Al/F4-TCNQ/NPB电荷产生层的叠层有机电致发光器件的特性研究

采用结构为LiF/Al/F4-TCNQ/NPB的电荷产生层,制备出了双发光单元叠层有机电致发光器件(OLED:Organic Light Emitting Device)。通过对比实验发现当F4-TCNQ层的厚度为8nm、Al层的厚度为5nm时,电荷产生层产生电荷的能力较强且具有良好的透光率。基于此,本文制备了发光层为CBP:6%Ir(ppy)3的叠层OLED,通过与单发光单元OLED的性能比较发现:采用LiF/Al/F4-TCNQ/NPB作为电荷产生层制备的叠层OLED的最大电流效率与功率效率分别为51.6cd/A、28.4lm/W,为单发光单元OLED的2.16倍、1.8倍,此外采用这种结构的电荷产生层有效解决了叠层OLED由于工作电压高而导致功率效率并未得到提升的问题;另一方面,采用有机材料F4-TCNQ代替传统无机金属氧化物作为电荷产生层中的电荷产生部分,能够避免无机金属氧化物高温升华对Al层薄膜的破坏,提升了器件的效率并且降低了器件的roll-off现象。     

高效叠层有机电致发光器件

采用Cs2CO3:Alq3/MoO3作电荷产生层,制备出高效双单元串联型叠层有机发光器件.双单元叠层有机发光器件发光性能受电荷产生层MoO3的厚度影响很大.当MoO3厚度为30 nm时,叠层器件表现出最好的器件性能,最大电流效率达到14.5 cd/A.在相当宽的低电流密度范围内,30 nm MoO3叠层器件的电流效率是...     

具有新型电荷产生层的叠层有机发光器件

研究了采用薄层WO3作为叠层有机发光器件电荷产生层时的性能并对其厚度进行了优化,器件的电荷产生层由Li掺杂的电子注入层和高透明的WO3组成.研究表明,薄层WO3具有很高的透明度,并能有效地产生和注入空穴.叠层器件性能与单发光单元器件相比较,其亮度及效率均有大幅提高,叠层器件的最大电流效率达到了4.2 cd/A,在相同的电流密度下,叠层器件的效率约为传统器件的2倍;同时,电荷产生层的性能与WO3薄膜厚度密切相关,WO3薄膜厚度为3 nm时,器件的效率在整个电流范围内都保持稳定.采用薄层WO3作为电荷产生层为制备高效叠层有机发光器件提供了一条有效的途径.     

不同荧光蓝光层厚度的OLED的制备与光电性能

采用蓝色荧光材料1p-TDPVBi结合绿色磷光材料2Ir(ppy)3掺杂到母体材料CBP作为绿光发光层,并且采用3BPhen作为电子传输层和激子阻挡层制备结构为ITO/m-MTDATA(50nm)/NPB(10nm)/p-TDPVBi(dnm)/CBP∶Ir(ppy)38%7nm/BPhen(60nm)/LiF(1nm)/Al的有机发光器件。实验结果表明:通过改变蓝光发光层p-TDPVBi的厚度,得到了高效率的有机发光器件,当p-TDPVBi厚度为5nm时,器件的电流效率和功率效率在4V时达到32.3cd/A和25.3lm/W,亮度在11V时达到31 020cd/m2。研究了p-TDPVBi厚度由3nm变化到9nm,OLED器件的电流密度-电压特性曲线、亮度-电压曲线及电流效率-电压和功率效率-电压等光电性能的变化。     

基于激基复合物主体的高性能OLED器件

为了得到低驱动电压、高光效的有机电致发光二极管(OLED),本文介绍了一种激基复合物mCP∶PO-T2T。首先通过测试mCP、TPBi、PO-T2T、mCP∶TPBi和mCP∶PO-T2T薄膜的光致发光光谱,确定了mCP∶TPBi、mCP∶POT2T具备激基复合物性能要求,并分别将上述两种激基复合物作为发光层主体,制备器件结构为HATCN(10nm)/TAPC(40nm)/TCTA(10nm)/mCP(10nm)/mCP∶X∶FIrpic(20nm,Y,15%)/X(50nm)/LiQ(2nm)/Al(120nm)的蓝光OLEDs。当X为PO-T2T,Y=42.5%(质量分数)时,对应蓝光器件开启电压为2.83V,功率效率和电流效率分别达到了35.5lm/W和33.1cd/A。在此基础上,将0.2%(质量分数)的黄光磷光材料PO-01掺入上述器件的发光层,得到了基于激基复合物主体的暖白光OLED,该器件获得了63.7lm/W的功率效率、61.8cd/A的电流效率以及19.9%的外量子效率,实现了具备低电压、高效率、色偏较小等优越性能的暖白光OLED。     

电子传输层中掺杂Ir(ppy)3改善白光OLED的效率

采用真空热蒸镀技术,制备了结构为ITO/NPBX(40nm)/rubrene(0.2 nm)/NPBX(5nm)/DPVBi(30nm)/TPBi:x%Ir(ppy)3(30nm)/LiF/Al的白光器件。利用Ir(ppy)3掺杂到电子传输层TPBi中,在掺杂层中提高了电子的迁移率,调整了空穴和电子的平衡,从而改善了白色有机电致发光器件的效率。当Ir(ppy)3的掺杂浓度为6%时,器件的电流效率最高,在驱动电压9 V时最大电流效率为10.66 cd/A,此时色坐标为(0.36,0.38);当电子传输层TPBi中不掺杂Ir(ppy)3时,白光器件的效率最低,在驱动电压10V时最大电流效率为1.69 cd/A,此时色坐标为(0.31,0.30)。掺杂浓度为6%的白光器件的电流效率是不掺杂白光器件的电流效率的6.3倍。     

以DCJTB为颜色转换层的三原色WOLED研究

对一系列蓝光和蓝绿光器件展开研究,发现结构为ITO/NPB(40nm)/mCP(5nm)/mCP∶FIrpic(30nm)/TPBi(2nm)/TPBi∶Ir(ppy)₃(10nm)/TmPyPB(40nm)/LiF(1nm)/Al的蓝绿光器件具有最佳光电性能,其电流效率高达38.3cd/A。基于该结构,结合采用红色荧光染料DCJTB制备的颜色转换层实现了三原色白色有机发光二极管(White Organic Light-emitting Diode,WOLED)。结果表明,器件性能可通过DCJTB浓度进行调控,当其浓度为0.7%时,实现了电流效率为23.9cd/A、色坐标为(0.35,0.43)及色温为5121K的WOLED,且电流密度从1mA/cm²变化到100mA/cm²,其色坐标仅漂移(0.005,0.003)。     

C545T对Al／MoO3复合阳极OLED性能的影响

制备了以Al／MoO3为复合阳极的有机电致发光器件,其结构为：Al／MoO3／NPB／Alq3：C545T（x%）／Alq3／LiF／Al。比较了不同掺杂浓度条件下OLED器件的电致发光特性。当C545T掺杂浓度为8％时,主客体间的能量转移最充分,器件的启亮电压为2．75V,器件在13V时获得最高亮度为27000cd／m^2,发光效率为6．97cd／A。用Fowler—Nordheim隧道效应理论和载流子注入机制,分析了以Al／MoO3为复合阳极的OLED器件性能。     

基于薄层铱配合物的有机电致发光器件研究

采用蓝色磷光染料bis[(4,6-diflourophenyl)-pyridinato-N,C2’)](picolinato) Iridium (III)(FI rpic)和黄色磷光染料bis[2-(4-tertbutylphenyl) benzothiazolato-N,C2,]iridium(acetylacetonate)[(t-bt)2 Ir(acac)]为超薄层,制备了结构为ITO/NPB/mCP/(t-bt)2Ir (acac)/mCP/Flrpic/mCP/TPBi/Mg:Ag的白色有机电致发光器件.通过调节磷光染料双超薄层Flrpic和(t-bt)2Ir(acac)的厚度,优化了白光器件的性能.结果表明,白光器件的最高电流效率为13.08 cd/A,最高功率效率为7.21 lm/W,发光光谱稳定,在9V时得到色坐标为(0.33,o.33)的标准白光,并且在较宽的电压范围内仅有(±0.08,±0.08)变化.这是由于超薄层FIrpic和(t-bt)2Ir(acac)形成的陷阱效应直接俘获电子和空穴,从而将载流子复合区域限制在一定范围内,不仅有利于增加激子的辐射发光效率,且提高了光谱的稳定性.     

阴极蒸镀和隔离层对有机发光二极管性能的影响

制备了简单结构的有机发光二极管(OLED)ITO/NPB/Alq3/Al/Ag。实验结果表明,快速蒸镀法制备的Ag阴极越厚,器件性能越差,而慢速蒸镀200nmAg阴极时器件性能也较差。在Alq3与Al阴极之间插入BCP/C60/LiF隔离层后,即使快速蒸镀法制备的Ag厚达280nm,器件的最大电流密度、最大亮度和最大电流效率仍分别高达248.6mA/cm2、5380.7cd/m2和3.52cd/A。隔离层不仅保护NPB和Alq3基本不被玻璃化,还很好地与Alq3和Al阴极匹配,大大提高了器件性能。     

载流子平衡方法提高量子点发光二极管效率的研究

尝试采用三种方式来平衡载流子的浓度,以提高量子点发光二极管(QLED)的外量子效率等性能:在正装结构(ITO/HIL/HTL/QD/ETL/EIL/金属阴极)的QLED的发光层和电子传输层中间插入超薄聚甲基丙烯酸甲脂(PMMA)电子阻挡层;在空穴注入和传输层方面,通过使用更加优化的HIL等来提高空穴注入和传输几率;在QD发光层方面,用短链配体来置换量子点的长链配体以增加载流子向量子点发光层中的传输效率等。在进行量子点配体交换的同时带来了量子点在正交溶剂中的可溶性优势,有利于QLED器件的全溶液法制备。     

Comparison between Equivalent Charge Model and Equivalent Dipole Model on Realistic Head Model

Equivalent source layer(ESL) imaging is an important kind of high-resolution electroencephalogram(EEG) imaging.It consists of two categories:equivalent dipole layer(EDL) and equivalent charge layer(ECL).Both of them are assumed to be located on or near the cortical surface and have been proposed as high-resolution imaging modalities or as intermediate steps to estimate the epicortical potential.Here,EDL and ECL based on a realistic head model are presented,both simulations and real data experiment are done to compare these two models.The results show that ECL can provide higher spatial resolution about source location than EDL does.     

Origin of Enhanced Hole Injection in Inverted Organic Devices with Electron Accepting Interlayer

Conventional organic light emitting devices have a bottom buffer interlayer placed underneath the hole transporting layer (HTL) to improve hole injection from the indium tin oxide (ITO) electrode. In this work, a substantial enhancement in hole injection efficiency is demonstrated when an electron accepting interlayer is evaporated on top of the HTL in an inverted device along with a top hole injection anode compared with the conventional device with a bottom hole injection anode. Current–voltage and space‐charge‐limited dark injection (DI‐SCLC) measurements were used to characterize the conventional and inverted N,N′‐diphenyl‐N,N′‐bis(1‐naphthyl)(1,1′biphenyl)‐4,4′diamine (NPB) hole‐only devices with either molybdenum trioxide (MoO₃) or 1,4,5,8,9,11‐hexaazatriphenylene hexacarbonitrile (HAT‐CN) as the interlayer. Both normal and inverted devices with HAT‐CN showed significantly higher injection efficiencies compared to similar devices with MoO₃, with the inverted device with HAT‐CN as the interlayer showing a hole injection efficiency close to 100%. The results from doping NPB with MoO₃ or HAT‐CN confirmed that the injection efficiency enhancements in the inverted devices were due to the enhanced charge transfer at the electron acceptor/NPB interface.     

Quantification of Temperature-Dependent Charge Separation and Recombination Dynamics in Non-Fullerene Organic Photovoltaics

Transient optical spectroscopy is used to quantify the temperature-dependence of charge separation and recombination dynamics in P3TEA:SF-PDI₂ and PM6:Y6, two non-fullerene organic photovoltaic (OPV) systems with a negligible driving force and high photocurrent quantum yields. By tracking the intensity of the transient electroabsorption response that arises upon interfacial charge separation in P3TEA:SF-PDI₂, a free charge generation rate constant of ≈2.4 × 10¹⁰ s⁻¹ is observed at room temperature, with an average energy of ≈230 meV stored between the interfacial charge pairs. Thermally activated charge separation is also observed in PM6:Y6, and a faster charge separation rate of ≈5.5 × 10¹⁰ s⁻¹ is estimated at room temperature, which is consistent with the higher device efficiency. When both blends are cooled down to cryogenic temperature, the reduced charge separation rate leads to increasing charge recombination either directly at the donor-acceptor interface or via the emissive singlet exciton state. A kinetic model is used to rationalize the results, showing that although photogenerated charges have to overcome a significant Coulomb potential to generate free carriers, OPV blends can achieve high photocurrent generation yields given that the thermal dissociation rate of charges outcompetes the recombination rate.     

Understanding Temperature‐Dependent Charge Extraction and Trapping in Perovskite Solar Cells

Understanding the factors that limit the performance of perovskite solar cells (PSCs) can be enriched by detailed temperature (T)‐dependent studies. Based on p‐i‐n type PSCs with prototype methylammonium lead triiodide (MAPbI₃) perovskite absorbers, T‐dependent photovoltaic properties are explored and negative T‐coefficients for the three device parameters (V_OC, J_SC, and FF) are observed within a wide low T‐range, leading to a maximum power conversion efficiency (PCE) of 21.4% with an impressive fill factor (FF) approaching 82% at 220 K. These T‐behaviors are explained by the enhanced interfacial charge transfer, reduced charge trapping with suppressed nonradiative recombination and narrowed optical bandgap at lower T. By comparing the T‐dependent device behaviors based on MAPbI₃ devices containing a PASP passivation layer, enhanced PCE at room temperature is observed but different tendencies showing attenuating T‐dependencies of J_SC and FF, which eventually leads to nearly T‐invariable PCEs. These results indicate that charge extraction with the utilized all‐organic charge transporting layers is not a limiting factor for low‐T device operation, meanwhile the trap passivation layer of choice can play a role in the T‐dependent photovoltaic properties and thus needs to be considered for PSCs operating in a temperature‐variable environment.     

一种新的MOS结构量子化效应修正模型

从载流子在 MOS结构反型层内的经典分布和量子化后的子带结构出发 ,提出了经典的和量子化的表面有效态密度 (SL EDOS:Surface layer effective density- of- states)的概念。利用表面有效态密度的概念建立了经典理论框架和量子力学框架内的电荷分布模型。该模型包含了强反型区表面电势的变化对载流子浓度的影响 ,具有很高的计算效率和稳定性。在模型基础上 ,研究了量子化效应对反型层载流子浓度和表面电势的影响。     

Origin of Reduced Bimolecular Recombination in Blends of Conjugated Polymers and Fullerenes

Bimolecular charge carrier recombination in blends of a conjugated copolymer based on a thiophene and quinoxaline (TQ1) with a fullerene derivative ((6,6)‐phenyl‐C₇₁‐butyric acidmethyl ester, PC₇₁BM) is studied by two complementary techniques. TRMC (time‐resolved microwave conductance) monitors the conductance of photogenerated mobile charge carriers locally on a timescale of nanoseconds, while using photo‐CELIV (charge extraction by linearly increasing voltage) charge carrier dynamics are monitored on a macroscopic scale and over tens of microseconds. Despite these significant differences in the length and time scales, both techniques show a reduced Langevin recombination with a prefactor ζ close to 0.05. For TQ1:PC₇₁BM blends, the ζ value is independent of temperature. On comparing TRMC data with electroluminescence measurements it is concluded that the encounter complex and the charge transfer state have very similar energetic properties. The ζ value for annealed poly(3‐hexylthiophene) (P3HT):(6,6)‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) is approximately 10^?4, while for blend systems containing an amorphous polymer ζ values are close to 1. These large differences can be related to the extent of charge delocalization of opposite charges in an encounter complex. Insight is provided into factors governing the bimolecular recombination process, which forms a major loss mechanism limiting the efficiency of polymer solar cells.     

The Curious Out‐of‐Plane Conductivity of PEDOT:PSS

For its application as transparent conductor in light‐emitting diodes and photovoltaic cells, both the in‐plane and out‐of‐plane conductivity of PEDOT:PSS are important. However, studies into the conductivity of PEDOT:PSS rarely address the out‐of‐plane conductivity and those that do, report widely varying results. Here a systematic study of the out‐of‐plane charge transport in thin films of PEDOT:PSS with varying PSS content is presented. To this end, the PEDOT:PSS is enclosed in small interconnects between metallic contacts. An unexpected, but strong dependence of the conductivity on interconnect diameter is observed for PEDOT:PSS formulations without high boiling solvent. The change in conductivity correlates with a diameter dependent change in PEDOT:PSS layer thickness. It is suggested that the order of magnitude variation in out‐of‐plane conductivity with only a 3‐4‐fold layer thickness variation can quantitatively be explained on basis of a percolating cluster model.