Nanostructured interfaces in thin hybrid and solar cells

Abstract

Global final energy consumption was around 8,428 Mtoe in 2008 and is expected to grow by 36% between 2008 and 2035 according to the International Energy Agency. At the same time, global warming has become an issue and objectives have been set to reduce the emissions of greenhouse gases (GHG). This leads to the need to develop low GHG emitting energy sources. This situation is ideal for the evelopment of solar cells, which produce electricity from sunlight without greenhouse gas emissions. Several technologies are being developed such as Si based solar cells, dye sensitized solar cells and thin hybrid and organic solar cells. The latter are relatively cheap and can easily be mass produced. However, their efficiency is low compared to silicon based cells and research is still in progress to solve that issue. One promising way of improving the efficiency of organic solar cells is to blend carbon nano-tubes (CNTs) as electron acceptors into the active layer of the cell. Those CNTs could serve as an electronic pathway towards the cell electrodes. This project aims to find cheap and easy ways of aligning the CNTs inside the active layer of the cell. This alignment can be useful for increasing the efficiency of the CNTs as electron pathways. Methods tried to align the CNTs are nanoimprint lithography (NIL), electric field assisted self-assembly and substrate rubbing. The samples are then characterized by using optical microscopy, atomic force microscopy, scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and electrical conductivity measurements. This thesis shows that thermal NIL as well as room temperature solvent assisted NIL can be effectively used to align CNTs in a polymer film. This is particularly visible in the Raman spectroscopy measurements. More experiments and the use of a polarised Raman spectroscope are required in order to conclude on the effectiveness of using substrate rubbing in order to align the CNTs.