Gavin Conibeer

Gavin Conibeer University of New South Wales Deputy Director, Photovoltaics Centre of Excellence Presentation Title: Third Generation Photovoltaics (PDF, 1.6Mb)

Abstract: To achieve the International Panel on Climate Change recommended 60% reduction in emissions by 2050—the minimum needed to offset the worst effects of climate change—a large scale implementation of sustainable and renewable energy technologies is required. Amongst these renewable energies, photovoltaics is the fastest growing technology with more than 30% growth per year over the last 10 years and more than 60% growth in 2007; although worldwide installation is still small. This growth in manufacture is currently driven by subsidies, primarily in Europe, but the increase itself leads to a learning effect as the technology matures, which brings down the cost per unit. In order to maintain the leverage this steep learning curve applies to unit price, a transition of technology from the first generation approaches based on single crystal wafer based solar cells to second generation thin film, with their much lower energy intensity and material usage, is required. However to project this downward pressure on price onto ever larger production volumes, a further generation change is required to push up efficiencies whilst still maintaining the low cost approaches of thin film cells. The reason that such third generation technologies can achieve such a “best of both worlds” result is that the vast majority of current production cells consist of only one absorbing semiconductor material. But such single semiconductor band gap devices have to compromise in their absorption of the very polychromatic solar spectrum, with a wide range of photon energies. This leads to significant energy losses through two main routes. At first, solar photons at less than the band gap energy are not absorbed at all and are wasted. Secondly, for photons well above the band gap energy, a large fraction of their energy is lost as heat in the device. Third generation devices use multiple energy levels, often in the form of several different semiconductor materials, to extract energy efficiently from a greater fraction of these photons. Examples of such approaches will be discussed, with specific mention of tandem solar cells that use quantum dot nanostructures based on silicon; devices which can up-convert low energy photons such that they are absorbed; and hot carrier cells which seek to extract the energy gained from high energy photons before it can be lost to the lattice. The status of and prospects for these approaches will be assessed. Biography: Dr. Gavin Conibeer received his PhD from Southampton University, UK, in Semiconductor Physics for tandem solar cells in 1995. He also has a BSc in Materials Science and MSc in Polymer Science from London University. Conibeer has held research positions at Oxford, Cranfield, Southampton, and Monash Universities where he has worked on most of the materials systems used in photovoltaics. Conibeer joined the University of New South Wales, Sydney, Australia in 2002 and was appointed a Deputy Director in the Photovoltaics Centre of Excellence in 2003, in charge of Third Generation Photovoltaics. This group of 22 researchers is investigating the fabrication of silicon, germanium and tin nanostructures in oxide, nitride or carbide matrices; up or down conversion of the incident solar spectrum; and hot carrier solar cells. Conibeer’s personal research interests encompass a wide range of third generation and advanced photovoltaic concepts, including silicon quantum dot based tandem solar cells, hot carrier solar cells, up-conversion and photoelectrochemical cells. He is author of over 100 publications including 35 journal articles.