Synthesis and Characterization of New Phosphorescent Heteroleptic Iridium (III) Complex by Using Tetrazole as an Ancillary Ligand for Organic Light-Emitting Diodes

The yellow emitting tetrazole based heteroleptic iridium(III) complex, bis(diphenylquinoline)iridium(pyridyltetrazole) [(DPQ)₂Ir(PyTz)], was synthesized and conformed by ¹H-,¹³C NMR spectral techniques. The purity was also confirmed by HPLC. The thermal, electrochemical, photophysical and electroluminescent properties were intrinsically investigated. The Ir(III) complex is thermally more stable having thermal decomposition temperature (T_d, 5% weight loss) more than 350°C and it shows very high glass transition temperature T_g-233°C. We have followed the easy and cost effective solution process for (DPQ)₂Ir(PyTz) device fabrication and achieved better performance yellow phosphorescent organic light-emitting diodes (PhOLEDs), maximum external quantum efficiency (EQE) of 5.68%, luminance efficiency 12.63 cd/A, and CIE coordinate of (0.56, 0.43).     

New Blue-Light Emitting Materials in White OLED Based on Solution and Vacuum Methods

New host material of 2-tert-butyl-9,10-bis(3′′,5′′-diphenylbiphenyl-4′-yl)anthracene [T-TAT] substituted t-butyl group was investigated in solution process WOLED device compared with 9,10-bis (3′′,5′′-diphenylbiphenyl-4’-yl) anthracene [TAT]. A two-color WOLED of a co-host system using solution process method was demonstrated. The device configuration was ITO / PEDOT:PSS (40 nm) / emitting layer (50 nm) / TPBi (20 nm) / LiF (1 nm) / Al. The emitting layer consisted of TAT or T-TAT, NPB, DPAVBi (blue dopant), and rubrene (yellow dopant). NPB was used to help hole carrier transport as well as blue host role. The device using the T-TAT compound as a co-host showed a luminance efficiency of 2.73 cd/A, which is 77% higher than TAT device of 1.54 cd/A at 20 mA/cm².     

Enhancement of organic thin-film solar cells by incorporating hybrid Au nanospheres and Au nanorods on a metallic grating surface

Abstract

In this study, we demonstrate the fabrication of hybrid plasmonic solar cells using gold nanoparticles (AuNPs). Two types of AuNPs, gold nanospheres (AuNSs) and gold nanorods (AuNRs), were incorporated in a hole transport layer (HTL) (PEDOT:PSS) on a metallic grating electrode. The organic solar cells (OSCs) structure comprised an indium-tin-oxide (ITO)-coated glass substrate/PEDOT:PSS:AuNSs:AuNRs/P3HT:PCBM/Al grating electrode. Adding AuNPs induced localized surface plasmon resonance (LSPR), while grating structured Al at the interface with a photoactive layer excited the propagating surface plasmons. Compared with a flat reference device, the proposed OSCs exhibited improved photovoltaic properties by increasing both the short-circuit current density (J_SC) and the power conversion efficiency (PCE) with large enhancements of 16.23% and 14.06%, respectively. The efficiency improvement was attributed to increased broadband absorption and improved electrical properties inside the thin-film devices.     

Highly Luminescent Red Phosphorescent OLED with Interfacial Layers for Hole Transport and Electron Injection

Four kinds of red phosphorescent organic light-emitting devices were fabricated and compared to investigate the effect of interfacial layers for hole transport and electron injection. 1 nm-thick LiF in the device A and C and 1 nm-thick Cs₂CO₃ in the device B and D were deposited as an electron injection layer between the anode and the electron transport layer, and 5 nm-thick layer of dipyrazion[2,3-f:2′,2′-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile[HATCN] was inserted as a hole transport interfacial layer between the hole injection layer and the hole transport layer only in the device C and D. Under a luminance of 1000 cd/m², the power efficiencies were 7.6 lm/W and 8.5 lm/W in the device A and B, and 8.6 lm/W and 13.4 lm/W in the device C and D. The quantum efficiency of the device D was 15.8% under 1000 cd/m² which was somewhat lower than those of the device A and C, but a little higher than that of the device B. The luminance of the device D was much higher than those of the other devices at a given votage. The luminance of the device D at 7 V was 23,710 cd/m², which was 13.0, 3.4, and 4.0 times higher than those of the device A, B, and C at the same voltage, respectively.     

以溶液法PEDOT∶PSS作为空穴传输层的免光刻背接触硅太阳电池

对PEDOT∶PSS(聚(3,4亚乙二氧基噻吩)-聚(苯乙烯磺酸))薄膜与Mg、Al和Ag三种金属接触后的I-V特性曲线进行了测试分析,发现Mg和Al与PEDOT∶PSS薄膜接触后呈现高电阻特性,可以起到绝缘隔离层的作用。在此基础上,以PEDOT∶PSS作为空穴传输层,以LiF作为电子传输层,以PEDOT∶PSS与Mg/Al的接触作为隔离层,不采用光刻工艺,设计制备了只需一次掩膜工艺的背接触太阳电池。通过在PEDOT∶PSS上采用热丝氧化升华技术制备MoO_x层,通过优化LiF薄膜的厚度,在抛光硅片上初步实现了开路电压最高为592 mV和效率最高为10.13%的背接触太阳电池。采用金属辅助腐蚀制备硅纳米线陷光结构改善前表面陷光效果,得到了开路电压为587 mV,短路电流密度为35.57 mA/cm²,填充因子为69.97%,效率为14.61%的背接触太阳电池。     

Synthesis and Photophysical Properties of Cationic Iridium Complexes using Oxazoline based Ancillary Ligands for Lighting Applications

In this study, we report the design, synthesis and characterization of two new cationic iridium(III) complexes employing oxazole based ancillary ligand, namely, and [Ir(ppz)₂(mbdiho)]PF₆ (Complex 1) and [Ir(dfppy)₂(mbdiho)]PF₆ (Complex 2) and its use in light-emitting electrochemical cells (LECs). The design is based on 2-phenylpyrazole (ppz) and 2-(2,4-difluorophenyl)pyridine (dfppy) as cyclometalating ligands and 2,2-Methylenebis[3a,8a-dihydro-8H-indeno[1,2]oxazole] (mbdiho) as ancillary ligand. The effect of substituents in the cyclometalating ligands on the photophysical and electrochemical properties of the complexes has been investigated. The synthesized complexes were used for the fabrication of LEC devices and studied their electroluminescent properties. The complexes incorporated LECs resulted in a higher luminance of 2820 cd m^?2 and current efficiency of 1.04 cd A^?1 for Complex 2 than Complex 1. Our work suggests that the light emission of cationic iridium complexes can easily tuned by the substituents present on the cyclometalating ligands which resulted in yellow and green emission for LECs based on Complexes 1 and 2, respectively.     

Efficient Charge Balance of Green Organic Light Emitting Diodes Using Mixed Charge Transporting Materials as the Host

The mixed layer for an emitting layer (EML) consists of two materials 4,4′,4′′-tris(N-carbazolyl)-triphenylamine (TCTA) and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) without host material. A series of EML structures were fabricated with three types of single mixed layers (mixing ratio 2:1, 1:2) and double mixed layers (mixing ratio 2:1/1:2), and the EML of using double mixed layer was optimized. The maximum luminous efficiency (LE) and quantum efficiency (QE) were 62.07 cd/A, 18.92%, respectively. Moreover, the roll-off ratio of LE was 20.42% at 20,000 cd/m². Interestingly, this result shows the roll-off ratio was reduced roughly 50% compared to the reference device.     

Efficient Bilayer Electrodes for Photosensitive Organic Heterostructure

The possibility of increasing the photosensitivity of organic heterostructures by using the bilayer transparent ITO electrodes with organic conducting polymer polyaniline, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) complex (PEDOT:PSS) and CuI has been verified experimentally. Photosensitive n-type organic semiconductor N,N′-dimethyl-3,4,9,10-perylenetetracarboxylic acid diimide (МРР) and p-type pentacene were chosen as components of these heterostructures. Usage of ITO/PEDOT:PSS bilayer electrodes leads to increasing the photovoltaic sensitivity of these heterostructures by 2–3 orders and by 1–2 orders when using CuI due to decreasing the recombination of excitons and increasing the potential barrier heights on the interface between the organic semiconductor and layers of PEDOT:PSS and CuI.     

Bulk Heterojunction Solar Cells with Ternary Mixed PTB7:PCDTBT:PC71BM Active Layers

We report on bulk-heterojunction solar cells fabricated based on ternary mixed solutions of two donors of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo [1,2-b:4,5-b’] dithiophene-2, 6-diyl] [3-fluoro-2- [(2-ethylhexyl) carbonyl]thieno[3,4-b]-thiophenediyl] (PTB7) and [N-9’-heptadecanyl-2,7-carbazole-alt-5,5-(4’,7’-di-2-thienyl-2’,1’,3’-benzothiadiazole)] (PCDTBT), and an accepter of [6,6]-phenyl C₇₁ butyric acid methyl ester (PC₇₁BM). The solar cells had a glass/ITO/NiO/PTB7:PCDTBT:PC₇₁BM/LiF/Al structure. Solar cells containing a 1-2% PCDTBT weight fraction showed a noticeable improvement in short circuit current density (J_sc), fill factor (FF), and power conversion efficiency (PCE). Solar cells with a 2% PCDTBT weight fraction exhibited an open circuit voltage (V_oc) of 0.77 V, J_sc of 13 mA/cm², FF of 0.42, and PCE of 4.23%. Possible mechanisms for the solar cell performance improvement by the introduction of the small amount of PCDTBT in the PTB7:PC₇₁BM active layer was discussed based on the active layer morphology changes and carrier transport mechanisms.     

Properties of flexible heterojunction based on ITO/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/pentacene/Al

The organic solar cell based on poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS)/pentacene (Pc) was fabricated using a flexible polyethyleneterephthalate (PET) substrate coated with conductive ITO layer and aluminum contact film formed on a Pc layer by electron beam deposition. The performed investigations of current–voltage characteristics indicate that the devices operate like Schottky diodes. Under illumination of an ITO/PEDOT:PSS/Pc/Al multilayer structure the photovoltaic effect is measured with open circuit voltages up to 0.5 V, short circuit current of 0.6 μA and fill factor 0.2. The spectral-photocurrent excitation profile covers a full range of visible light (380–700 nm).     

Synthesis and Characterization of Violet Light Emitting Polymer based on Fluorene and Dimethylsilane

New fluorene based light emitting polymer, poly[(4-(9,9-didecyl-9H-fluoren-2-yl) phenyl)dimethyl(phenyl)silane] (PFDPS), was synthesized by palladium-catalzed Suzuki coupling reaction. The obtained copolymer was characterized by ¹H-NMR, and IR-spectroscopy. The polymer showed good solubility in common organic solvents and weight average molecular weight of 16,300 with polydispersity index of 1.4. The maximum photoluminescence of the solution and film of the polymer was observed at 392 nm and 410 nm, respectively.

The double-layered device with the configuration, ITO/PEDOT/PFDPS/LiF/Al structure has a turn-on voltage at about 5.5 V and maximum brightness of 9.40 cd/m², and emitted violet light at 414 nm.     

Asymmetric Ferroelectric Switching Based on an Al/PVDF Langmuir-Blodgett Nanofilm/PEDOT:PSS/Al Device

We prepared highly oriented ferroelectric poly(vinylidene fluoride) (PVDF) Langmuir–Blodgett (LB) nanofilms by an assistance of amphiphilic poly(N-dodecylacrylamide) (pDDA) nanosheets. In the nanofilms, semi-crystalline PVDF contains abundant polar β crystals, a parallel packing of PVDF all-trans molecules. Combing semi-conductive PEDOT:PSS and ferroelectric PVDF LB nanofilms, we fabricated a sandwiched capacitor (Al/PVDF LB nanofilm/PEDOT:PSS/Al). The capacitor shows asymmetric hysteresis curves and high remanent polarization values.     

Synthesis of a BDT-based small-molecule acceptor with dye end groups for organic photovoltaic cell application

ABSTRACT

An acceptor-donor-acceptor (A–D–A)-type small molecule, BDT-IN, having a benzo[1,2-b:4,5-b']dithiophene (BDT) unit as its electron-donating core (D) and an 1,3-indanedione (IN) unit as its electron-withdrawing end group (A), was synthesized by Knoevenagel condensation. The BDT-IN film showed broader UV absorption with a greater red shift (λ_max = 622 nm) than that of the BDT-IN solution (λ_max = 570 nm). The organic photovoltaic cells were fabricated with an ITO/PEDOT:PSS/poly(3-hexylthiophene): BDT-IN/LiF/Al configuration, and showed a power conversion efficiency of 0.23%.     

Synthesis and crystal structure of the iridium(I) carbene complex with a pair of hydrogen wing tips

The iridium(I) cyclooctadiene complex with two (3-tert-butylimidazol-2-ylidene) ligands [(H-Im^tBu)₂Ir(COD)]⁺PF₆^? (C₂₂H₃₂PF₆IrN₄) has been prepared, and its crystal structure is determined by X-ray diffraction. Complex exhibits slightly distorted square planar configurations around the metal atom, which is coordinated by two H-Im^tBu ligands and one cyclooctadiene group. The new iridium carbene complex has a pair of hydrogen wing tips. The Ir?C_carbene bond lengths are 2.066(5) and 2.052(5) Å, and the bond angle C?Ir?C between these bonds is 95.54(19)°. The dihedral angle between two imidazol-2-ylidene rings is 86.42°.     

Starburst-Type Carbazole Trimers as Host Materials for Solution-Processed Phosphorescent OLEDs

Novel starburst-type carbazole trimers SB-1 and SB-2 were developed as hole-transporting host materials for phosphorescent organic light-emitting diodes (PhOLEDs). The triplet levels (T₁s) of SB-1 and SB-2 were determined as at 2.81 and 2.73 eV, respectively. Also, these compounds afforded stable amorphous thin films upon spin-coating, and thus it was found that they are applicable to solution-processed devices. Indeed, blue PhOLEDs were fabricated by a solution method using SB-1 and SB-2 as host materials, where better device performance was obtained for the SB-1-based device due to its higher-lying T₁.     

Annealing effects on output characteristics of solution processable vertical organic light-emitting transistor (VOLET)

Abstract

The influence of annealing temperature on the output characteristics of solution processable vertical organic light-emitting transistor (VOLET) was investigated. Poly[(vinylidenefluoride-co-trifluoroethylene] (PVDF-TrFE) and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) have been used as a dielectric and emissive layer, respectively, in a silver nanowire (AgNW) sourced VOLET. It was found that the performance of the VOLET is the best after annealed at 100 oC. A high polarization of the PVDF-TrFE promotes more charged carrier to be accumulated at AgNW/MEH-PPV interface. Surface morphology and photoluminescence results show that a high surface roughness of MEH-PPV exhibit bright emission due to reduction of internal reflection of light emission.     

面向器件应用的PEDOT:PSS薄膜的光电稳定性研究

PEDOT:PSS(聚3, 4-亚乙基二氧噻吩-聚苯乙烯磺酸盐)薄膜因其良好的导电性、透光性、机械柔韧性以及溶液可加工性而被广泛应用。提高PEDOT材料的电导率以及光电稳定性对其器件应用有重要意义。在本文中,首先用旋涂法制备PEDOT:PSS薄膜,然后采用硫酸后处理技术提高其电导率,并将硫酸处理后的薄膜分别放置于空气、氧气、氮气中以及太阳光照下30 d,研究薄膜的光电稳定性及老化机制。实验结果表明:太阳光照是影响薄膜光电性能稳定性的主要因素,而硫酸处理有效地去除了过量的PSS成分,使薄膜的稳定性变好。通过比较老化前后薄膜的光吸收谱和光电子能谱(XPS)发现,在老化过程中薄膜发生了光氧化降解,这是影响薄膜光电稳定性的原因之一。     

Crystal Structures of Two Palladacycles from the C–H Activation of 2-(Thiophen-2-yl)pyridine

Abstract  

A C,N-bound palladacycle dimer has been synthesised by reaction of 2-(thiophen-2-yl)pyridine, LH, with palladium acetate in acetic acid. Characterisation by single crystal X-ray diffraction showed the palladacycle dimer, [(L)Pd(OAc)]₂, to crystallise in the monoclinic space group P2₁/n with cell parameters a = 9.5853(1) ?, b = 19.1332(3) ?, c = 12.3889(2) ?, β = 103.732(1)°. Reaction of [(L)Pd(OAc)]₂ with triphenylphosphine afforded a trans-substituted monomeric complex, [(L)PdPPh₃(OAc)] which was also analysed using single crystal X-ray diffraction. [(L)PdPPh₃(OAc)] crystallises in the monoclinic space group P2₁/c with cell parameters a = 9.4839(1) ?, b = 11.0427(2) ?, c = 26.0770(4) ?, β = 95.022(1)°.     

Molecular structure of [(tBu)2Al(μ-Cl)]2

The crystal and molecular structure of [(^tBu)₂Al(μ-Cl)]₂ has been determined. The bond lengths and geometry about aluminum are similar to that in [Me₂Al(μ-Cl)]₂ and [(Mes)₂Al(μ-Cl)]₂ suggesting that the geometry about the aluminum is defined by the steric repulsion between the alkyl groups on adjacent aluminum centers and not steric congestion between ligands on individual aluminum centers. Crystal data: Triclinic, $P\bar 1$ ,a=6.514(1),b=8.628(2),c-11.236(2)c=11.236(2) Å, α=102.05(3), β=105.32(3), γ=103.47(3)°,V=567.2(3) ų,Z=1,R=0.063,R _w =0.067.     

GaP:Mg layers grown on GaN by MOCVD

We have investigated the growth of magnesium-doped GaP (GaP:Mg) layers on GaN by metalorganic chemical vapor deposition. The hole carrier concentration increased linearly from 0.8×10¹⁸ to 4.2×10¹⁸ cm⁻³ as the Bis(cyclopentadienyl) magnesium (Cp₂Mg) mole flow rate increased from 1.2×10⁻⁷ to 3.6×10⁻⁷ mol/min. However, the hole carrier concentration decreased when the CP₂Mg mole flow rate was further increased. The double crystal X-ray diffraction (DCXRD) rocking curves showed that the GaP:Mg layers were single crystalline at low CP₂Mg molar flow. However, the GaP:Mg layers became polycrystalline if the CP₂Mg molar flow was too high. The decrease in hole carrier concentration at high CP₂Mg molar flow was due to crystal quality deterioration of the GaP layer, which also resulted in the low hole mobility of the GaP:Mg layer.