Examinando por Autor "Mallavia, Ricardo"

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analytical evaluation of the ratio between injection and space charge limited currents in single carrier organic diodes
(IEEE, 2008) ALvarez, Angel Luis; Arredondo, Belén; Romero, Beatriz; Quintana, Xabier; Gutiérrez, Araceli; Mallavia, Ricardo; Otón, José Manuel
An analytical, complete framework to describe the current-voltage (I-V) characteristics of organic diodes without the use of previous approaches, such as injection or bulk-limited conduction is proposed. Analytical expressions to quantify the ratio between injection and space-charge-limited current from experimental I-V characteristics in organic diodes have been derived. These are used to propose a numerical model in which both bulk transport and injection mechanisms are considered simultaneously. This procedure leads to a significant reduction in computing time with respect to previous rigorous numerical models. In order to test the model, different diode structures based on two different polymers: poly(2-methoxy-5-{3',7'-dimethyloetyloxy}-p-phenylenevinylene) (MDMO-PPV) and a derivative of the poly(2,7-fluorene phenylidene) [PFP:(CN)(2)], have been fabricated. The present model is excellently fitted to experimental curves and yields the microscopic parameters that characterize the active layer.
Influence of electrical operating conditions and active layer thickness on electroluminescence degradation in polyfluorene-phenylene based light emitting diodes
(Elsevier, 2009) Romero, Beatriz; Arredondo, Belén; Alvarez, Angel Luis; Mallavia, Ricardo; Salinas, A; Quintana, Xabier; O, José Manuel
We have studied the influence of the electrical working conditions (voltage or current biased). and the active layer thickness on electroluminescence (EL) properties of polymeric light emitting diodes based on poly-[9,9-bis(6'-cyanohexyl)-2,7-fluorene-alt-co-1,4-phenylene], [PFP:(CN)(2)]. Diodes with different active layer thicknesses (55-140 nm) have been fabricated and characterized. Temporal evolution of the spectra at constant bias and current, as well as the spectral evolution with the current, has been performed. Excitation photoluminescence has been used to discriminate between intrinsic and defect-related transitions. The relative spectral area arising from defects has been quantified by means of Gaussian deconvolution for different device excitations. Active layer thickness has been observed to play an important role on the emissive spectral shape. In thick samples EL tends to resemble fluorescence from the pristine material. In contrast, thinner samples clearly show two additional bands related to defects: the first one is structured in the range 470-510 nm, which is proposed to be due to electron accumulation in the active layer, and a second band at 535 nm. arising from on-chain keto defects due to the presence of oxygen. The role of the electron blocking character of the PEDOT:PSS on the spectral shape, as well as the influence of the active layer thickness on the oxygen concentration, are discussed