RESUMEN
Carrier transport and trapping was investigated in poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) layers by thermally stimulated currents (TSC) depending on the exciting light spectral range. The upper edge of the spectra ranged from 1.77 eV up to 3.1 eV to assure selective excitation of the defect states. The TSC curves were shown to be a superposition of several thermally activated processes, i.e., carrier generation from trapping states and thermally stimulated mobility growth according to the Gaussian disorder model. The extrinsic excitation resulted in 0.15 eV photoconductivity effective activation energy values, which decreased down to 0.05 eV for the intrinsic excitation. The deeper states with activation energies of 0.28-0.3 eV and 0.8-0.85 eV were identified too. The results are direct indication by photo-thermo-electrical methods of distributed in energy trapping and transport states with the standard deviation of the density of states of about 0.015 eV.
RESUMEN
We have investigated charge carrier transport and trapping in the layers of [poly-(2-methoxyl, 5-(3,77dimethyloctyloxy)] para phenylenevinylene (MDMO-PPV). To reveal distribution of the trapping states the thermally stimulated current method was applied using the varying excitation conditions by light and applied voltage. To assure the selective excitation of the defect states close to the band gap edges, both extrinsic and intrinsic excitation by the light passed through the long-pass color filters with the cut-off energies ranging from 1.77 eV up to 3.1 eV was employed. Carrier transport conditions were varied by increasing applied electric field from 5 x 10(4) V/cm up to 6 x 10(5) V/cm. The effective thermal activation energy of material conductivity was dependent both on the spectral region of the exciting light and applied electric field. The superposition of several thermally activated processes, i.e., carrier generation from the trapping states and thermally stimulated mobility growth according to the Gaussian disorder model, was revealed. The energy distribution of the trapping state density was shown to follow the Gaussian distribution function. We had demonstrated that carrier trapping is effectively influenced by the extended defect states with the effective activation energy values ranging from 0.05 eV up to 0.15 eV with maximum located at about 0.07-0.08 eV. Moreover, deeper states with activation energies of 0.28-0.3 eV and 0.8-0.85 eV were identified. The results are direct indication by photo-thermo-electrical methods of distributed in energy trapping and transport states with the standard deviation of the density of states of about 0.015 eV.
Asunto(s)
Membranas Artificiales , Nanoestructuras/química , Nanoestructuras/ultraestructura , Polivinilos/química , Transporte de Electrón , Transferencia de Energía , Ensayo de Materiales , Tamaño de la Partícula , TemperaturaRESUMEN
Charge carrier transport and trapping was investigated in organic solar cell structures consisting of poly-3-hexylthiophene blended with the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester in 6:5 weight ratio. The analysed devices having solar efficiency of 3.7 per cent were produced in the inverted layer sequence. The fill factor of the IV characteristics was as high as 68 per cent. It was demonstrated that despite of such relatively high fill factor carrier trapping is effectively involved in the charge transport phenomena. The density of the trapping states was evaluated to be up to 10(20) division by 7 x 10(21) cm(-3) and their activation energy was about 0.18 eV. At such high densities these states may probably act as transport states, limiting carrier mobility. The results were analyzed by taking into account carrier thermal generation from traps as well their mobility variation according to the Gaussian disorder model. The mobility parameters obtained by both methods demonstrated good coincidence.