PV-21 is the UK's inorganic solar photovoltaic (PV) research programme / this proposal is for a renewal for the second four year cycle. The Consortium has sharpened its focus on the science that will deliver our medium to long term goal of 'making a major contribution to achieving competitive PV solar energy'. In its initial period of activity, the Consortium has put in place lab-scale facilities for making three main types of solar cells based on thin film absorbers - copper indium diselenide, cadmium telluride and ultra thin silicon - using a range of methods. In the renewal programme, these three 'Technology Platforms' form the basis for testing new processes and concepts. To reduce costs, we shall concentrate on critical materials and PV device issues. For large-scale PV manufacture, the materials costs dominate, and together with module efficiency determine the cost per kW peak. A closely related issue is sustainability. For example the metal indium is a key component in PV, but is rare and expensive ($660/kg in 2007). Reducing the thickness of semiconductor by one millionth of a metre (1 micron) in 10% efficient cells with a peak generating capacity of 1GW would save 50 tonnes of material. The renewal programme therefore includes work on both thickness reduction and on finding alternative sustainable low cost materials (absorbers and transparent conductors). To increase efficiency we shall work on aspects of grain boundaries and nanostructures thin films as well as on doping. Nanostructures will also be exploited to harvest more light, and surface sensitization of thin film silicon cells by energy transfer from fluorescent dyes will also be investigated as a means of making better use of sunlight and substantially reducing the required film thickness to as low 0.2 microns. In order to ensure a focus on cost effectiveness, the renewal programme includes a technical economics package that will examine cost and sustainability issues. Future links between innovative concepts and industry are ensured by a 'producibility' work package. Two highly relevant 'plus' packages have been submitted alongside the renewal proposal, these being on a) thin film silicon devices, grain engineering and new concepts, and b) new absorber materials. The Consortium will also continue to run the successful UK network for PV materials and device research, PV-NET, which is a forum for the UK academic and industrial research communities. The Supergen funding mechanism has enabled the Consortium to assemble and fully integrate a critical mass of PV researchers in the UK, and the work packages outlined in the proposal interweave the skills and capabilities of seven universities and nine industrial partners. PV-21 is also plays an important role in skills development, with nine PhD students due to be trained in the first cohort. The EPSRC Supergen funding mechanism is absolutely vital for the continued growth and strength of the UK PV materials research effort.