University of Bristol
Our efforts to harness the abundant solar flux with man-made photovoltaic (PV) technology to generate electricity have, to date, been far less effective than the near unity efficiency regularly achieved by plants. To meet the ever-growing global energy demands, it is imperative for our society to develop renewable and more efficient PV devices that can take full advantage of the abundant solar flux. With lower costs and higher efficiencies, these technologies will be well placed to replace fossil fuel based electricity generation, which is a large contributor to irreversible climate change.
As well as benefits, sunlight harbours threats: the ultraviolet (UV) component of sunlight is potentially very harmful for life on Earth. Deoxyribonucleic acid (DNA) is the source code for all living organisms. The precise sequence of molecules in the famous double helical structure of DNA contains all the information required for cell growth, development and function. If DNA absorbs the UV light, damaging photochemical reactions can be initiated, such as ejection of an electron or bond breaking. These can lead to destruction of our genetic code and cancerous mutations.
Absorption of light by molecules and materials increase the internal energy. In many cases, the excited molecules have sufficient energy to overcome barriers to structural re-arrangements, or can transfer this energy to different molecules. One of the main goals of this proposal is to understand how energy is redistributed and partitioned in arrays of molecules and solid state materials. In DNA, if this energy is trapped in excited states for a significant period of time, the excess energy can be used to form dangerous charge separated electrons and radical cations. For PVs, fast charge separation is highly desirable and can determine their efficiency. These processes of energy redistribution occur on very fast timescales, often those commensurate with the period of a vibration; 10-100 fs (1 fs = 10^-15 s). Currently we do not have the technology to visualise the motion of individual atoms or electrons on that timescale. We can, however, infer their motions using spectroscopy with laser pulses with femtosecond pulse durations. Using accurate time delays between laser pulses, we can take snapshots of bulk molecular and nanomaterial properties. From these measurements we deduce the route and timescale of energy flow through systems.
By understanding the directions and timescales of energy flow, and how energy and electrons are redistributed and transferred in arrays of molecules and bulk materials, we will seek to develop mechanisms on the molecular level that underpin photodamage in DNA and the efficiency of PV devices. These insights will provide a platform for protect against cancer in living cells, and to guide the design of the next-generation thin film PV materials.
Interests and expertise (Subject groups)