Hybrid Optoelectronic and Photovoltaic Materials based on Silicon Nanocrystals and Conjugated Polymers

Abstract

Hybrid material, which combines advantages of both organic and inorganic materials, might offer potential for design of novel type of low cost devices with superior performance (Schneider et al., 2000; Liu et al., 2008). The large choices for the organic and inorganic structures offer the possibility to obtain materials with attractive physical and chemical properties. The morphology of hybrid material at nanoscale might lead to very different properties from crystalline solids. Particularly molecular structure polymers, conformation and orientation can have a major effect on the macroscopic properties of novel material (Coakley et la.,2003). Nanotubes are a promising subclass of nanomaterials owing unique one-dimensional geometric features that can allow engineering the polymer based material morphology at low cost. Nevertheless, nanotubes fabrication with diameter comparable with exciton diffusion lengths of polymers (~ 15 nm) is still a problem. It has to be noted that among the nanotubes with small diameter (< 5 nm), carbon-based discovered by Iijima (Iijima 1991) were the first to gain recognition in academia (Marte et al., 2001; Harris, 2002; Wang et al., 2009). Novel synthetic strategies for generating nanotubes from inorganic materials have been recently also widely investigated and developed (Tenne et al., 1992; Zhao, et al., 2004). It is believed that fiber/nanotube-polymer based arrays of material have much lower reflectance and enable fabrication of thicker devices with increased absorption compared with thin films. One of the promising type of polymers used in variety of applications are the conjugated conductive ones (Inzelt, 2008). It has to be noted that in traditional polymers e.g. polyethylenes, the valence electrons are bound in sp3 hybridized covalent bonds (Inzelt, 2008). Therefore sigma-bond electrons have low mobility and do not contribute to the electrical conductivity. Contrary to that conducting polymers have backbones of contiguous sp2 hybridized carbon centers. As a result a valence electron on each center resides in a pz orbital, which is orthogonal to the other three sigma-bonds. Then electrons within the band become more mobile particularly when it is partially emptied. This advantage combined with the mechanical properties (flexibility, toughness, malleability, etc.) make them favorable also for optoelectronic applications as an active material.