Photosensitive in wide spectral region composites based on polyphenylenevinylene

Optical and photovoltaic properties of polyphenylenevinylene derivative – poly(2-methoxy-5-(3-,7-dimethyl-octyloxy)-1,4-phenylenevinylene (MDMO-PPV) and its composites with high (40 %) concentration polymethine dyes (PD) – meso-Cl and hexaindoletricarbocyanine (HITC) films have been studied. Two H-aggregates of dyes with different energies that weakly depend on the molecular structure of dyes, is formed in MDMO-PPV with PD in composites films. The efficiency of photogeneration of charge carrier by these aggregates is greater than the efficiency of photogeneration of charge carriers by the quasi-isolated molecules of dye. It results in substantial expansion of the absorption region (in comparison with the absorption region of molecules in solution) and photosensitivity in the side of higher energies. The presence of PD aggregates in the films MDMO-PPV influences on their photosensitivity that depends on PD molecular structure. This dependence can be caused by interaction between the molecules of MDMO-PPV and dye. In composites MDMO-PPV/HITC, the value of interaction is low and practically does not influence the efficiency of photogeneration of charge carriers by MDMO-PPV molecules, which give a considerable contribution to formation of the photovoltage in 2-3 eV regions. The interaction of meso-Cl and MDMO-PPV molecules is stronger, and this, probably, results in considerable decrease of photovoltage in the region of the excitation of MDMO-PPV

Fabrication and characterization of solution-processed methanofullerene-based organic field-effect transistors

The fabrication and characterization of high-mobility, n-channel organic field-effect transistors (OFET) based on methanofullerene [6,6]-phenyl C61-butyric acid methyl ester using various organic insulators as gate dielectrics is presented. Gate dielectrics not only influence the morphology of the active semiconductor, but also the distribution of the localized states at the semiconductor-dielectric interface. Spin-coated organic dielectrics with very smooth surfaces provide a well-defined interface for the formation of high quality organic semiconductor films. The charge transport and mobility in these OFET devices strongly depend on the choice of the gate dielectric. The electron mobilities obtained are in the range of 0.05-0.2 cm2 V-1 s-1. Most of the OFETs fabricated using organic dielectrics exhibit an inherent hysteresis due to charge trapping at the semiconductor-dielectric interface. Devices with a polymeric electret as gate dielectric show a very large and metastable hysteresis in its transfer characteristics. The observed hysteresis is found to be temperature dependent and has been used to develop a bistable memory element

Charge carrier mobility in sulphonated and non-sulphonated Ni phthalocyanines: experiment and quantum chemical calculations

The objective of this interdisciplinary paper was to study theoretically and experimentally the electronic part of charge carrier transport in the class of sodium salts of sulphonated Ni phthalocyanine as candidates for p-type channels in organic field-effect transistors. These materials were selected because of their enhanced solubility as compared to their non-sulphonated counterparts. The values of the field-effect charge carrier mobility determined on the OFET structures using NiPc(SO3Na)x films were much higher than the charge carrier mobility obtained on the respective device prepared from non-substituted phthalocyanine. In order to explain differences between charge carrier mobility of sulphonated and non-sulphonated Ni phthalocyanines, quantum chemistry studies of molecular aggregates were performed. Quantum chemistry modeling of the semiconductive molecular systems is new and progressive – we highlighted factors at the molecular level which led to the enhancement of the charge carrier mobility in systems containing SO3Na groups