Renewable Energy & Materials for Energy
Energy efficient and low cost materials are the two main drivers in Renewable Energy Research. Our programme spans cheap organic materials through to record breaking efficient inorganic materials for photovoltaics as well as magneto-caloric materials for environmentally friendly and efficient magnetic refrigeration.
The very highest solar cell power conversion efficiencies are achieved using multi-junction solar cells. Much of the QPV research group’s activity is concerned with the development of semiconductor materials that can efficiently absorb sunlight in the 1-2um wavelength range, which can push multi-junction solar cell efficiency over 50%. A collaboration with the University of Tokyo resulted in the demonstration of a 1.15eV sub-cell formed of aggressively strain balanced GaAsP/InGaAs quantum wells. We established that under certain growth conditions, this strain- balanced structure spontaneously formed quantum wire in well structures with carrier lifetimes in excess of 1μs. An alternative approach to this problem using GaAsSbN has been evaluated in partnership with IQE PLC and Nangyang Technical University, SiGeSn with IQE PLC and Translucent Inc and finally GaAsBi with Sheffield University.
Organic Solar Cells
Finding new materials to harvest and store solar energy is critical to future clean energy supply. We study the physics, chemistry, materials science and device engineering of new, solution processible materials for solar cells. These include organic semiconductors such as conjugated polymers and small molecules, hybrid inorganic:organic materials and - with Dr Piers Barnes - dye sensitised and perovskite materials. The central aim of the group’s research is to understand how chemical structure and physical organisation of materials controls material properties and device function.
Our main research activities span: The device physics of organic and hybrid solar cells. We study the factors controlling current generation and charge recombination in solar cells, such as the role of trap states, doping and interface recombination. We use detailed analysis to determine the sources of loss in practical devices and find ways to reduce such losses.
Academic Staff: Professor Lesley Cohen
We are currently funded through an Innovate UK grant together with the Materials department at Imperial College and Cambridge UK to bring magnetic materials closer to application for energy efficient and environmentally friendly magnetic refrigeration: We have recently participated in a European wide programme on solid state magnetic cooling (DRREAM) and an EPSRC programme grant on materials for energy applications. We use our unique characterisation tools to study the magnetic, thermal and magnetocaloric properties of a range of materials. We examined the influence of the local demagnetisation field on the nucleation and growth of the magnetocaloric transition. The work helped identify the importance of the magnetic dipole interaction and thermal linkage across the material as components to the transition process itself. We also studied the limitations of the magnetocaloric effect in managanites, showing how the intrinsic properties that made this system so important for colossal magnetoresistance two decades ago, contribute to their relatively modest performance for solid state magnetic cooling applications.
Solid Oxide Fuel Cells
Academic Staff: Professor Lesley Cohen
The work builds on the development of an optical fuel cell for monitoring Raman active processes in real time. We have used this system and a furnace Raman system to provide information on the reduction and oxidation processes associated with the formation of secondary phases in gadolinium doped ceria, one of the widely used electrolyte materials for solid oxide fuel cells.