Single-walled carbon nanotube – polymer hybrids as hole transporting layers for organic solar cells

In this thesis, new types of single-walled carbon nanotube (SWNT)-Polymer/single molecule nanostructures were prepared and successfully used as hole transporting layers in both conventional and inverted organic solar cells thereby pushing the carbon nanotube based organic solar cell efficiency close to 10%. The first part of the thesis focuses on investigating the binding of nanotubes to Spiro-OMeTAD. A novel dual-shell nanostructure was prepared by first wrapping SWNTs with a monolayer of semiconducting polymer (F8BT/P3HT) that forms Type-I / Type-II heterojunctions with the nanotube, and subsequently binding a large number of small molecules (Spiro-OMeTAD) onto the [Polymer-NT] nanohybrids. This strong interaction leads to a significant improvement in PL emission intensity which we associate with the debundling of the nanotube. In the second part of the thesis, the properties of a new polymer wrapped single walled carbon nanotubes (C8-SWNTs) were investigated and shown to successfully remove metallic impurities from different carbon nanotube starting materials. In addition, highly selective wrapping (~99.3%) of only one SWNT species (6,5) can be made possible by optimising the chain length of the polymer. PLE studies show that there is a ~71 fold reduction in the intensity of other SWNT species compared to the SWNT starting material. Finally, the third part of the thesis focusses on the fabrication of high efficiency organic solar cells (~9.4%) using highly semi-conducting Polymer-SWNT nanohybrids as hole transporting layers. A simple polymer exchange technique was used to produce ~99.5% pure semiconducting P3HT-SWNT nanohybrids. We used these nanoybrids as Hole Transporting Material (HTM) in the fabrication of the devices and were able to achieve high efficiencies with improved stability.