Synthesis, fabrication and characterization of poly[3-3′(vinylcarbazole)] (PVK) Langmuir-Schaefer films

Poly[3-3′(vinylcarbazole)] (PVK) was synthetized with N-vinylcarbazole as monomer by oxidative polymerization with ferric chloride. The resulting polymer was then deposited on various solid supports by using Langmuir-Schaefer (LS) method. The pressure-area isotherm of PVK revealed the possibility of compact monolayer formation at air-water interface. Different layers of PVK were doped with iodine vapours. Both scanning probe microscopy and optical microscopy images indicated a good uniformity of the films. The morphology and the thickness of PVK films were investigated using atomic force microscopy. The voltammetric investigation of I₂ doped PVK showed a distinctive electrochemical behaviour. The photoinduced charge transfer across a donor/acceptor (D/A) hybrid interface provided an effective method to study the photoelectrochemical properties of the composite LS films.     

Microstructures and photovoltaic properties of C60 based solar cells with copper oxides,CuInS2, phthalocyanines,porphyrin, PVK,nanodiamond, germanium and exciton diffusion blocking layers

Abstract

Organic solar cells have a potential for use in lightweight, flexible, inexpensive and large scale solar cells. However, significant improvements of photovoltaic efficiencies are mandatory for use in future solar power plants. One of the improvements is donor–acceptor proximity in the devices, which are called bulk heterojunction solar cells. Bulk heterojunction is an efficient method to generate free charge carriers, and the charge transfer is possible at the semiconductor interface. The purpose of the present work is to fabricate and characterise C₆₀ based solar cells with copper oxides, CuInS₂, phthalocyanines, porphyrin, poly-vinylcarbazole, nanodiamond, germanium and exciton diffusion blocking layers. In the present work, C₆₀ and fullerenol [C₆₀(OH)_10–12] were used for n-type semiconductors, and metal copper oxides, metal phthalocyanine derivative, porphyrin and poly-vinylcarbazole were used for p-type semiconductors. In addition, nanodiamond and germanium based molecules were added into the active layers of the solar cells. The novel aspect of the research is to investigate the relation between properties and microstructures of the solar cells using transmission electron microscopy, X-ray diffraction and electronic structure calculation. The impact of the research concerns the study of organic solar cells by means of microstructural analysis, property measurements and theoretical calculations.     

Deep blue/ultraviolet microcavity OLEDs based on solution-processed PVK:CBP blends

There is an increasing need to develop stable, high-intensity, efficient OLEDs in the deep blue and UV. Applications include blue pixels for displays and tunable narrow solid-state UV sources for sensing, diagnostics, and development of a wide band spectrometer-on-a-chip. With the aim of developing such OLEDs we demonstrate an array of deep blue to near UV tunable microcavity (μc) OLEDs (λ ∼373–469 nm) using, in a unique approach, a mixed emitting layer (EML) of poly(N-vinyl carbazole) (PVK) and 4,4′-bis(9-carbazolyl)-biphenyl (CBP), whose ITO-based devices show a broad electroluminescence (EL) in the wavelength range of interest. This 373–469 nm band expands the 493–640 nm range previously attained with μcOLEDs into the desired deep blue-to-near UV range. Moreover, the current work highlights interesting characteristics of the complexity of mixed EML emission in combinatorial 2-d μcOLED arrays of the structure 40 nm Ag/x  nm MoO_x/∼30 nm PVK:CBP (3:1 weight ratio)/y  nm 4,7-diphenyl-1,10-phenanthroline (BPhen)/1 nm LiF/100 nm Al, where x = 5, 10, 15, and 20 nm and y = 10, 15, 20, and 30 nm. In the short wavelength μc devices, only CBP emission was observed, while in the long wavelength μc devices the emission from both PVK and CBP was evident. To understand this behavior simulations based on the scattering matrix method, were performed. The source profile of the EML was extracted from the measured EL of ITO-based devices. The calculated μc spectra indeed indicated that in the thinner, short wavelength devices the emission is primarily from CBP; in the thicker devices both CBP and PVK contribute to the EL. This situation is due to the effect of the optical cavity length on the relative contributions of PVK and CBP EL through a change in the wavelength-dependent emission rate, which was not suggested previously. Structural analysis of the EML and the preceding MoO_x layer complemented the data analysis.     

基于MEH—PPV／PVK混合发光层的白光PLED发光机理探讨

分别采用聚合物MEH-PPV、PVK、MEH-PPV和PVK混合溶液及MEH-PPV、PVK与OXD-7混合溶液作为发光层材料制成了4种相似结构的PLED显示器件,并对上述器件进行了光谱测试.对其光谱分析发现,MEH-PPV的光谱主要集中在红、黄领域,短波区光谱强度弱,可以忽略不计;PVK的光谱范围较宽,短波区域光谱强度相对较高,但与长波区光谱强度相比则较低;MEH-PPV:PVK混合发光材料不仅出现了MEH-PPV和PVK所有光谱的光线,而且实验发现波长在500～540 nm的光线亮度随着波长的增加亮度增强,即出现了所谓的反常区,对此作者提出两种模型对该反常区进行了详细解释;加入电子传输材料OXD-7后,PLED器件短波长部分的光线强度增加,这主要是由于OXD-7能够有效增加电子的传输效率,进而有效提高激子的能量.     

Photorefractivity and transmission‐type holograms of a poly(N‐vinylcarbazole)‐based composite with N‐4‐nitrophenyl‐(l)‐prolinol as chromophore

The photorefractivity of a poly(N‐vinylcarbazole)/2,4,7‐trinitro‐9‐fluorenone/N‐4‐nitrophenyl‐(l)‐prolinol/N‐ethylcarbazole composite was investigated by two‐beam coupling and degenerate four‐wave mixing experiments. The composite in a weight ratio 35 : 1 : 50 : 15 exhibited a 22% steady‐state diffraction efficiency and 70 cm⁻¹ two‐beam coupling coefficient at the applied external field of 55 V/μm. Zero applied field transmission‐type holograms were observed in the photorefractive sample as well as the spin‐coated thin film. The dynamic decay of diffraction light indicated that there existed two contributors with different phase‐shift, and the slow decay time can be as long as several h under continuous illumination by the readout beam. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 447–451, 2000     

Avoiding trap states in poly(n-vinylcarbazole) thin films

Optical properties of poly(n-vinylcarbazole) (PVK) thin films are revisited. Steady-state emission spectra put in evidence a strong red band whose intensity increases with decreasing temperature when the solid state PVK film is excited by a continuous 375 nm laser line. This red band is assigned to the emission from PVK aggregate states which act as trap states for the monomeric PVK triplet high energy (blue) excitons. At the same low temperatures, these trap states can be avoided when the excitation of the PVK film is made by a 355 nm pulsed laser line with 10 Hz repetition rate. The red band was also observed to compete with the emission of guest poly(3-octadecylthiophene) (PODT) molecules in a PVK/PODT sequential bilayer structure. Different optical geometries enabled us to show that the exciton energy transfer effect from PVK donor to PODT acceptor states dominates the scenario in the bilayer structure, suppressing almost completely the trap state emissions.     

The role of exciplex states in phosphorescent OLEDs with poly(vinylcarbazole) (PVK) host

Polymer light emitting diodes (PLEDs) may revolutionize lighting and display industries. PLEDs would enable printing of display or lighting panels on large area substrates that could substantially reduce fabrication costs by avoiding expensive vacuum processes presently used in OLED technologies. PVK is one of the most popular hosts for blue PLEDs. However, PVK has very poor electron transport properties and oxadiazole based electron dopants, e.g. PBD or OXD-7, are used to improve charge transport. This is generally ascribed to capture and transport of electrons on the PBD or OXD-7. Here we show that this is not necessarily the only reason for improved efficiency upon PVK doping. We demonstrate that devices with PVK doped with PBD or OXD-7 have emission lasting up to 1 ms which in some cases may be greater than prompt emission from excitons formed initially on the dopant. This long-lived emission is arising mainly due to formation of an exciplex between the PVK and PBD/OXD-7. This exciplex state then repopulates dopant iridium complexes over a long period of time giving very long-lived emission. We also note that this exciplex-fed long-lived emission from heavy metal complexes is observed in several PLEDs with PBD and PVK (and also OXD-7) doped with blue or green iridium phosphors indicating this to be a general phenomenon.     

Properties of polymer light‐emitting diodes coated on surface‐treated ITO/glass substrates

We fabricated blue polymer light‐emitting diodes (PLEDs) with indium tin oxide (ITO)/PEDOT : PSS/PVK/PFO‐poss/LiF/Al structures. All of the organic film layers were prepared by the spin‐coating method on plasma and heat‐treated ITO/glass substrates. The dependences of the optical and electrical properties of the PLEDs on the plasma and heat treatment of the ITO film and the introduction of poly(N‐vinylcarbazole) (PVK) layer were investigated. The AFM measurements indicated that the surface roughness of the ITO transparent film was improved by the plasma and heat treatment. In the emission spectra, the intensity of the excimer peaks of the PFO‐poss [polyhedral oligomeric silsesquioxane‐terminated poly(9,9‐dioctylfluorene)] emission layer were decreased for the PLED device with the PVK film layer compared with the one without the PVK layer. The maximum current density, luminance and current efficiency of the PLEDs were found to be about 470 mA/cm², 486 cd/m² at an input voltage of 12 V and 0.55 cd/A at 100 cd/m² in luminance, respectively. The color coordinates (CIE chart) of the blue PLEDs were in the range of x = 0.17 ～ 0.20, y = 0.13 ～ 0.16, and the peak emission spectrum was about 430 nm, showing a good blue color. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

CdSe／PVK纳米晶薄膜及其电致发光特性

以巯基乙酸（RSH）为稳定剂，在水溶液中合成CdSe纳米晶，用表面活性剂将分散在水溶液中的纳米颗粒转移到有机溶剂中，与具有电荷输运性能的有机聚合材料复合。作为电致发光（EL）器件的工作层，得到较强的位于600nm附近的CdSe纳米晶的带边发射，以及较弱的位于420nm附近的来自聚合物的发射。器件EL强度首先随着外加电压的增加而增加，当电压超过26V时，EL强度开始下降。器件的电流-电压（I-V）特性基本符合二极管特性，表明器件是受载流子注入限制的。     

聚乙烯基咔唑对稀土络合物发光特性的影响

本文报导了稀土红色荧光络合物－Eu(TTA)m复合体系与聚乙烯基咔唑（PVK）共混体系的光致发光和电致发光性质。通过对吸收光谱和发射光谱的测量,可知在光致发光中存在PVK向Eu(TTA).复合体系的能量传递,但在较大的掺杂浓度下仍存在来自PVK的发光.在电场激发条件下,此共混体系的电致发光仅有稀土络合物的特征发光而很难看到PVK的特征发光.并且这种电致发光器件的稳定性明显改善,另外在器件结构中加入电子传输层可明显提高器件的发光效率.