Transport model for disordered organic nanocomposites
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Transport model for disordered organic nanocomposites Andrés Vercik1 1 Nanotechnology, Biosensors and Devices Laboratory, University of São Paulo, Av. Duque de Caxias Norte 225, 13635-900, Pirassununga - SP, Brazil ABSTRACT Electric transport in disordered media is usually explained in terms of different transport regimes, such as SCLC (Space Charge Limited Current) or TCLC (Trap Charge Limited Current) regimes. These models lead to exponential dependencies of the current on voltage, e.g., quadratic for SCLC or higher order for TCLC, with transition regions between them where fitting is poor. Alternatively, a statistical distribution in space and energy of the disordered traps, e.g., Gaussian or exponential, allows explaining transport in disordered materials. In this work, we propose a modeling based on the density of states (DOS) function, fitted from normalized differential conductivity curves obtained from experimental current-voltage curves. In general a Gaussian function is used for low energies whereas one or more exponential functions are used for higher energies. The proposed model is used to reproduce experimental current-voltage curves of organic nanocomposites, with gold and silver nanoparticles within chitosan matrixes. A unique expression is obtained for a very accurate fitting the experimental current-voltage characteristics in the whole voltage range without transition regions. INTRODUCTION Organic materials are attractive for many applications, such as OLEDs for displays or lightning devices, solar cells and memories based on polymeric nanocomposites [1]. The main advantages of organic electronics are the low cost and the possibility of making large area and flexible devices. Bio-inspired electronic materials allow fabricating eco-friend and non-polluting devices in sustainable electronics. Bioresorbable materials used in temporary implantable biomedical electronic devices, such biosensors, based on biodegradable materials, are also promising. All these applications require a deep knowledge of the transport properties to predict their optimal operation. The aim of this work is to contribute to understanding the electrical properties of disordered organic nanocomposites by modeling their current-voltage characteristics. Many biomaterials are suitable for use in organic electronic systems due to their electrical properties. Natural and synthetic polymeric biomaterials, such as chitosan and poly(vinyl alcohol) (PVA), are electrical insulators and could be used as gate dielectrics in electronic industry, despite some drawbacks, such as significant hysteresis and large gate leakage currents, can limit their use [2]. The electronic transport in organic materials has been extensively studied, in general assuming a space charge limited current regime with a quadratic dependence of the current on voltage, with partially or totally filled traps, and a trap-filling region with a higher power law on voltage. Assuming electric field dependent mobilities, e.g., a Poole-Frenkel mobility, other shapes of the curve
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