Surface properties of quantum dots for next generation solar cells
There is an urgent requirement to make better use of the 120,000 TW of power provided by the Sun. In order to make solar power generation economically viable, the next generation of solar cells must be cheaper and less costly in energy terms to produce. The development of wet-chemistry synthetic routes for the fabrication of high-quality nanoparticles or ‘quantum dots’ has created an opportunity for the exploitation of these quantum dots as the light-harvesting elements in future solar cells. In principle they offer a cheap and green solution to providing solar power.
Example of a prototype solar cell: Incoming sunlight is absorbed by a quantum
dot, creating an electron hole pair (or exciton) which must then be rapidly
separated, the electron travelling to the photoanode via metal oxide nanorods,
and the hole being transported to the photocathode via a conducting polymer.
At the heart of the nanocell device is a semiconductor quantum dot that harvests the incident light, creating an electron-hole pair, which is separated to produce a photocurrent. A potential obstacle to widespread exploitation is the limited chemical and photochemical stability of these quantum dots – in particular to oxidation of their surfaces, which affects the properties of the dot, and can impair the extraction of charge carriers from it. It is vitally important that we understand how the energy levels in the dot match up with the materials surrounding it, how charge is transported from it, and how this is affected by its surface properties – and this is the task of this PhD project. This project will use X-ray photoelectron spectroscopy (XPS) to understand the surface properties of the dot (including its stability, and the bonding of other cell components to it.) In addition a number of synchrotron and laser spectroscopies will be used to understand the electronic structure of the dot, and how charge is transferred from it when sunlight is absorbed. Synchrotron work will be carried out at the European synchrotron radiation sources such as SOLEIL near Paris, or MAXlab in Lund, Sweden.