An organic light-emitting device (OLED) having a double-heterostructure of ITO/NPB/DCMdoped Alq3/BCP/Alq3/MgAg was constructed to form a narrow recombination zone where both charge carriers and excitons are confined, thus resulting in efficient electron-hole recombination and energy transfer. It was found that though luminance efficiency was enhanced, the low electron mobility of BCP resulted in higher driving voltages and limited the improvement of power efficiency. Significant improvements on both quantum efficiency and power efficiency were achieved by replace 1,3,5-tri(phenyl-2-benzimidazoly)-benzene (TPBI) for BCP, and were correlated with its high electron mobility. Device performance was further improved in the structure ITO/NPB/DCM-doped Alq3/TPBI/LiF/MgAg with a maximum luminance efficiency 6.03cd/A and a power efficiency of 5.94 lm/W.

The acrylic system consisting of a casting syrup [made of polymethyl methacrylate (PMMA) dissolved in methyl methacrylate (MMA) monomer] and triethylene glycol dimethacrylate (TEGDMA) monomer was polymerized by two different methods. One of these methods was made by thermal decomposition of benzoil peroxide (BP) as initiator, and the other one, used the promoted decomposition of BP using dimethyl p-toluidine (DMT). Both types of polymerization were carried out by bulk polymerization in closed test tubes. Since the polymerization reactions were over, the polymer obtained from the two methods were very different each other in appearance and, when characterization analysis were performed those gave evidence of different behavior between the two types of polymers. The characterization study was carried out using Scanning Electron Microscopy (SEM) to observe the morphology and microstructure in the polymers. Fourier Transform Infrared (FTIR), Raman and micro-Raman to analyze differences on the chemical compositions in the polymer bulk. Differential Scanning Calorimetry (DSC) to evaluate the thermal behavior, Dilatometry to determine the final cure shrinkage after polymerization reaction in the two types of polymers.

This report describes the synthesis of photocrosslinkable dendrimers with peripheral cinnamamide residues, which exhibit both photoisomerization and photodimerization, and their photochemical and photophysical properties in dilute solutions and polymer matrices. Photoirradiation with 313 nm gave rise to monotonous decrease in the absorbance of trans-cinnamamide at 270 nm as a result of the photochemical reactions of the cinnamamide residues. Spectral analysis revealed the changes in the photoproduct distribution of trans- and cis-photoisomerized and photodimerized cinnamamide groups to be a function of the exposure energy. In dilute solutions, the first-generation dendrimer displayed preferential formation of cis-isomer of the cinnamamide, whereas the photodimerization took place more favorably for the third- and fifth-generation dendrimers. The photochemical behavior was strongly dependent on the dendrimer generation rather than the concentration, probably due to the extent of steric crowding among the cinnamamide residues at terminal positions. Furthermore, the third- and fifth-generation dendrimers showed capturability of a benzophenone derivative into the macromolecules and triplet-triplet energy transfer in the photocrosslinkable dendrimers. This novel phenomenon of the triplet-triplet energy transfer in the dendritic cavities suggests potential applicability to design and fabricate novel optical and electrical molecular devices.

The charge transporting properties of N, N'-dipheny l-N, N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD), TPD doped with 5,6,11,12- tetraphenylnaphthacene (rubrene), and TPD doped with 4-(dicyanomethylene)-2-methyl-6-(pdimethylaminostyryle) 4H-pyran (DCM1) were examined by time-of-flight (TOF) technique between 180-300K. The dependence of the mobility on electric field and temperature for undoped and doped TPD was investigated. Reductions in hole mobility shows that both dopants act as hole traps in TPD. Computational results of TPD also account for the effective hole conduction in pristine TPD film.

Hybrid organic-inorganic solar cells promise to utilize the advantages of each class of materials and their complementary nature to produce power efficiently with inexpensive processing. Combining the efficient charge transport typical of inorganic semiconductors with the solution processibility of semiconducting polymers, nanocrystal-polymer photovoltaics hold tremendous potential[1[. Electronic energy levels of inorganic and organic semiconductors tend to be significantly staggered, creating a large energetic driving force for charge transfer. However, the hybrid approach requires control over the interface between dissimilar materials in order to mix them on the nanoscale. This mixing creates the very high area interface responsible for charge creation. Molecular level control of the interface, absent in current designs, could optimize charge separation.

Electrically conductive immiscible polymer blends containing high impact polystyrene (HIPS), liquid crystalline polymer (LCP) and a low content of conductive carbon black (CB) were studied to establish and understand the correlation between composition, electrical properties and the morphology of filaments produced at different melt flow conditions. The HIPS/LCP/CB blend containing 30% LCP and at least 2 phr CB reveals a stable resisitivity throughout the shear rate range applied in a capillary rheometer. Interesting structure alterations were observed for the LCP and CB components as a result of melt flow processing. Unusual sensing properties of liquids were found for the blends containing LCP.

The X-ray structural analysis of di-L-valine selenate monohydrate has been carried out (P21, a=6.181(2), b=18.675(3), c=15.342(4)Å β=90.14(2)°, V=1770.8(7) Å3, Z=4, R=0.0532 for 3057 observed reflections). The crystal structure is formed by selenate anions, L-valinium cations and water molecules (in the ratio of 1:2:1) interconnected by a system of hydrogen bonds. The FTIR (298-90 K temperature range) and FT Raman spectra were recorded and interpreted. DSC measurements were carried out in the temperature range 95-363 K. Quantitative SHG measurements of di-L-valine selenate monohydrate and tri-L-valine selenate were carried out on powdered samples.

In this work electrically detected magnetic resonance (EDMR) is used to study the electronic properties of poly(2-methoxy-5-(2'-ethyl-hexoxy)-1,4-phenylene vinylene) (MEHPPV) diodes. Two kinds of MEH-PPV diodes were characterized. The first one was a bipolar light emitting diode whose structure was ITO/MEH-PPV/Al. In this diode the EDMR signal is composed of two lines, a line that can be fitted by a lorentzian with peak-to-peak linewidth of 5.0 ± 0.5 G and the other best fitted with gaussian line with a linewidth of 24 ± 1 G. The g factor of both components is 2.002 ± 0.001 and signals were only observed at forward bias. The second diode is a hole only device, with a structure ITO/MEH-PPV/Au, the EDMR signal in this case is dominated by a gaussian line with peak-to-peak linewidth of 5 ± 1 G and average g factor of 2.0014 ± 0.0002. In high forward bias (V > 30 volts at T = 130K) a second line could be observed with a linewidth of 10 ± 2 G and a g factor of 2.0012 ± 0.0004. The signal from both types of diodes is quenching, and tipically10-5 in amplitude. The EDMR signal is assigned to the spin-dependent fusion of two like-charged polarons. Our results indicate that the narrower component is coming from positive polarons while the broader to negative polarons.

A new host-guest electro optic (EO) polymer, in which a chromophore can be reacted with the polymer main chain during poling to give the corresponding side-chain EO polymer, has been prepared for improving EO effect and its thermal stability. Polyisoimide (PII) synthesized from 2, 2-bis (4-aminophenyl) hexafluoropropane and oxydiphthalic anhydride and Disperse Red 1 (DR1) were used as a host and a guest, respectively. A model compound reaction and Infrared spectra of the host-guest film after annealing at various temperatures show that the reaction between the isoimide groups in PII and the hydroxyl groups in DR1 occurs around 140 °C. The glass transition temperatures of the resulting EO polyamic aicd ester-imide copolymer with 0, 10, 20 and 30 wt. % of chromophore concentration were 275, 219, 160, and 124 °C, respectively. The EO coefficient obtained at a wavelength of 1.55 νm was 5.3 and 10.5 pm/V from the EO polymer film with 20 and 30 wt. % DR1. The EO signals exhibited only a slight decay at high temperature due to the chemical reaction between the host and guest during poling.

In order to realize the vast potential offered by semiconducting polymers in emissive display technologies, it is important to understand the structure-property relationships that govern their performance. This paper will focus on one such relationship in the most widely studied class of polymers viz. poly(phenylene-vinylene) (PPV) derivatives. We have synthesized oxadiazole containing PPV copolymers varying the composition and sequence distribution of the oxadiazole moiety in the chain. We find that a statistically random copolymer performs 50% better in EL efficiency than the corresponding alternating copolymer with the same chemical composition, and 3 times better than the homopolymer without any oxadiazole moieties.

The current voltage characteristics of C60 thin film sandwich structures fabricated by vacuum deposition on indium tin oxide (ITO) with an aluminium top electrode are presented and discussed. A strongly non-linear behavior and a sharp increase in the device conductivity was observed at relatively low voltages (∼2V), at both room and low temperatures (20K). At room temperature the system is seen to collapse, and in situ Raman measurements indicate a solid state reduction of the fullerene thin film to form a polymeric state. The high conductivity state was seen to be stable at elevated voltages and low temperatures. This state is seen to be reversible with the application of high voltages. At these high voltages the C60 film was seen to sporadically emit white light at randomly localized points analogous to the much documented Electroluminescence in single crystals.

Conventional organic light-emitting diodes (OLEDs) having electrically doped carrier injection and transport layers with high conductivity exhibit extremely low driving voltages, which is due to the formation of radical anions and cations and ohmic contacts at the electrode interfaces. We report here an inverted OLEDs with indium-tin-oxide (ITO) bottom contact as cathode for electron injection. The device comprise an intrinsic 8-tris-hydroxyquinoline aluminum (Alq3) emission layer sandwiched in between n- and p-doped charge transport layers.

We investigate the geometric and electronic structure of porphyrin-fullerene based supramolecular system in which have an extremely long-lived charge-separated state have been achieved, using first principle calculations. The results suggest that the LUMO state of this supramolecule is localized on the fullerene and HOMO state is localized on the porphyrin moiety.

An overview of recent results concerning the injection and transport of holes in a range of conjugated fluorene polymers, provided by the Dow Chemical Company, is presented.

Time-of-flight measurements in poly(9,9-dioctylfluorene) (PFO) are performed in a range of electric fields and temperatures (200-415 K). It is found that annealing at 380 K results in an irreversible increase of the hole mobility by one order of magnitude. Analysis of the TOF data within the Gaussian disorder model of Bassler and coworkers shows that this effect mainly contributes to the mobility prefactor 0, which grows from 2.3x10-2 to 2.6x10-1 cm2/Vs after annealing, while the disorder parameters σ and Σ increase only slightly.

Dark-injection transient measurements are performed in poly(9,9-dioctylfluorene-co-bis-N,N'-(4-methoxyphenyl)-bis-N,N'-phenyl-1,4-phenylenediamine) (PFMO) and poly(9,9-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)-bis-N,N'-phenyl-1,4-phenylenediamine) (PFB) polymers for the range of electric fields and in a wide range of sample thicknesses. The lowest studied thickness (0.22 μm) for PFB is much closer to typical device thicknesses (≤0.1 μm) than the thicknesses (∼1 μm) required for TOF measurements. It is shown that there are no significant differences in hole transport across the range of thicknesses from 0.22 μm to 1.1 μm indicating that for this material TOF technique can be a reliable tool to characterise materials for device operation. There is found to be an influence on stability of the metal counter-electrode used to perform dark-injection measurements. Specifically Ag and Au are found to give less stable structures than Al.

Within recent years, the development of polymer-fullerene plastic solar cells has made significant progress. In such devices, an efficient charge generation takes place via photoinduced charge transfer between the photoexcited conjugated polymer and acceptor-type fullerene molecules. Due to the paramagnetic nature of the radical species, the photoinduced charge transfer can be studied by means of light induced electron spin resonance (LESR) techniques. We carried out W-band (95 GHz) LESR at high magnetic field strengths. Two well separated line groups with a strong anisotropic structure were detected for the composite MDMOPPV: PCBM. From the line shape analysis, we obtained an environmental axial symmetry for the positive polaron P+ and a lower, rhomboedric symmetry for the fullerene anion. The signals were found to be independent of each other with different spin-lattice relaxation times; hence, the radical species can be investigated separately. In order to study the bulk transport properties, we carried out admittance spectroscopy on the ITO/PEDOT:PSS/MDMO-PPV:PCBM/Al device. Two frequency-dependent contributions to the device capacitance with the activation energies 9 meV and 177 meV were found. For the very shallow trap state, we assume a bulk impurity, whereas the latter one is assigned to an interfacial defect state, located at the composite- aluminium interface.

Recent doping experiments in n-type perylene diimide (PPEEB) semiconducting thin films showed an unexpected quadratic dependence of electrical conductivity upon dopant molecule concentration. We propose that singly-ionized dopant pairs outnumber ionized unpaired dopants and dominate conductivity. Random association into dopant pairs during spin coating then explains the quadratic dependence. Classical calculations confirm that dopant pairing reduces the binding energy of the easiest-to-ionize electron. Our model agrees with the measured conductivity activation energy and magnitude, assuming typical electron mobility in the crystal. The random distribution of dopants implies their distribution cannot equilibrate during the spincoating process.

We present device simulations for p-channel organic field effect transistors. The current conservation equation and Poisson's equation are solved self-consistently in two dimensions in the drift-diffusion approximation. We focus on modeling transistor structures consisting of a gate electrode, a silicon dioxide gate insulator, and a pentacene or a conjugated polymer layer as the active (channel) material. The source and drain contacts are taken to be deposited directly on the gate insulator (bottom contact structure). We examine the effects associated with differences in charge carrier injection for different source and drain contact materials. It is also shown that, if the organic material immediately adjacent to the contacts has poor conduction properties, ‘parasitic’ source and drain series resistances that depend on the contact/organic injection barrier height as well as the channel material mobility can result.

Hardness measurements in ion implanted polymers are complicated by the fact that the hardness of the material varies as a function of depth within the modified layer. This effect is induced by the distribution of deposited energy, which produces a depth-dependent variation in microstructure. We have used the depth-sensing nano-indentation technique to investigate the mechanical properties of thin films of ion-beam modified aromatic polymers deposited onto silicon substrates. The depth of the ion-modified surface layer was determined using the load variation technique from the hardness and elastic module depth profile and the depth dependence of the power law coefficient of the unloading curve.

Low cost, high volume manufacturing processes are envisioned for solution processable organic semiconductor integrated circuits (IC) fabrication. The organic IC may be the low cost solution for driving electronic devices, i.e. smart cards, RFID tags, flexible displays, personal area networks, and body area networks. This study investigated the manufacturability of organic electronics (organic field effect transistors (OFETs), organic light emitting diodes (OLEDs), etc.) using commercially available printing technologies and materials systems qualified for use in microelectronic products. The evaluated contact printing technologies were pad printing and screen-printing; the non-contact printing technologies were ink jetting and micro dispensing. The material system selection for transistor structures and active layers was based on printing technology requirements and commercial availability. The materials were polymer thick film conductors and insulators, conductive nano-particle suspensions, and organic polymer systems. A series of material property characterization and printing process development studies were conducted. Several OFET designs were created and functional all printed organic transistors were demonstrated. The device electrical performance was characterized.

Charge-based deep level transient spectroscopy (Q-DLTS) has been used to study the defect states that exist within poly(p-phenylene vinylene) (PPV), a semiconducting polymer with a band gap of about 2.4 eV. The technique allows the determination of activation energies, capture cross-sections and trap concentrations. In some circumstances, it is also possible to distinguish between minority and majority carrier traps. The structures investigated here consisted of ITO/PPV/MgAg light emitting diode (LED) devices. Two types of trapping centres were found. The first type has activation energies in the range 0.49 – 0.53 eV and capture cross-sections of the order of 10-16 – 10-18 cm2. It shows a Poole-Frenkel, field assisted-emission process. This level has been identified as a bulk acceptor-like majority carrier (i.e., hole) trap. The second type has activation energies in the range 0.40 – 0.42 eV and capture cross-sections of the order of 10-19 cm2. This level has been identified as a minority carrier (i.e., electron) trap. This second trap type is therefore expected to limit minority carrier injection into the PPV layer within the LED, and hence reduce electroluminescence under forward bias conditions.