Photoconductivity Measurements of Organic Polymer/Nanostructure Blends
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Photoconductivity Measurements of Organic Polymer/Nanostructure Blends David Black and Shashi Paul1 Emerging Technologies Research Centre, Hawthorn Building, DeMontfort University, The Gateway, Leicester, England, LE1 9BH ABSTRACT In an attempt to produce low cost and high quality polymer/nanoparticle blends for use in hybrid organic/inorganic photovoltaic devices we prepared blends of dihexylsexithiophene and tetragonal barium titanate particles. These polymer nanoparticle blends were deposited as films by spin coating and sublimation. The films were characterised and compared using a wide range of techniques; The electrical photoconductivity analysis of these structures carried out using an HP4140B picoammeter and a solar simulator after aluminium gap cell electrodes had been deposited on the films by sublimation, spectroscopic studies (UV-VIS) were carried out to understand the photoconductivity measurements and ellipsometry was used to determine the thickness of the films. The photoconductivity of the spin coated films was the highest reaching 8.5x 10-10A at 20 V, the sublimed films reached ~4 x 10-10A at 40V. This is thought to be due to the thinness of the sublimed films combined with the inhomogeneous distribution of nanoparticles compared with the spin coated film. Sublimed films have been shown by others to be better structured than spin coated films, if this property can be utilized with further optimization of the sublimation process then this technique offers the potential to produce very thin high quality films for use in organic and hybrid photovoltaic devices. INTRODUCTION Hybrid organic/inorganic photovoltaic devices comprising a blend or blends of polymers and inorganic nanostructures offer the potential of flexible devices with a small number of steps in the fabrication process. These devices are excitonic in nature, when an organic photoconductive material absorbs a photon of an appropriate wavelength, an excited state is created. It has been demonstrated by other groups such as that of Roman and other that the efficiency of photovoltaic devices is increased by incorporating nano-particulates into the organic photoconductive materials [1]. This work follows on from our previous work using tetragonal barium titanate to increase the permittivity of both insulating and conducting polymers with the aim of producing nanoparticle polymer matrices suitable for inclusion in hybrid organic/inorganic photovoltaic devices [2]. Commercially available barium titanate (BT) nanoparticles are cubic in nature and do not have the ferroelectric characteristics needed to increase the permittivity of polymers and hence we used tetragonal BT, prepared as described below, which does have the required properties. It has also been demonstrated previously by Kim et al [3] that BT is generally not highly soluble and by attaching a suitable ligand it can be more easily made into a suspension for spin coating. An initial study has been undertaken in our lab to understand photoconductivity of the blends of dihexy
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