Enhancement of hole mobility in lead sulfide nanoparticle doped polymer
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In recent years there has been increasing interest in the applications of hybrid organic-inorganic materials in electrical devices such as solar cells, photo detectors, field-effect transistors, light-emitting diodes etc. One of the promising composite structures which have been found useful for such application is a heterogeneous mixture of a polymer and semiconductor nanoparticles (quantum dots). The advantage of such a structure is that the optical properties of the quantum dots, which are related to the presence of quantum confinement, can be combined with good mechanical properties of the polymer, which can work both as a binder and as a matrix providing other electrical and optical functionalities. In this thesis, we report that charge carrier mobility in poly(9-vinylcarbazole) (PVK) can be enhanced by doping it with lead sulfide (PbS) nanoparticles. This result is a new confirmation of the effect first observed on cadmium sulfide nanoparticles in PVK and it is discussed in terms of the previously proposed mean free path model 1,2 as well as the band structure of the nanoparticles and its alignment with that of the host material. The mobility of holes (dominant carriers in the PVK host materials) was measured using the conventional time-of-flight technique with the injection of holes from a selenium layer. Though photocurrent transients exhibit features typical of dispersive transport in an amorphous semiconductor, certain deviations from the original Scher-Montroll theory are observed. Strong dependence of the carrier mobility on field and temperature indicate Poole-Frenkel-like activated hopping transport.