The demand for renewably generated electricity will only increase. Common photovoltaic modules consist of single p-n junction solar cells made of silicon or the more cost effective CdTe or Cu(In,Ga)Se2. All have an upper theoretical light to electric power conversion efficiency of 33 %, known as the Shockley-Queisser limit (SQL). This is breakable when the sunlight is used more effectively than is done in single junction devices. Multi-junction devices made of III-V semiconductors do surpass the SQL with efficiencies of around 39 % under normal conditions and around 46 % under concentrated light, showing the potential of multi-junction and concentrator solar cells, albeit at very high cost. Breaking the SQL using cost-effective materials still needs to be demonstrated and devices will require new materials, more components and greater structural complexity.The aim of this Doctoral Training Unit is to create a cohort of scientists with expertise in advanced photovoltaic concepts necessary to overcome the SQL. This will be achieved by a stimulating and ambitious research and training programme. The research will focus on multi-junction and concentrator solar cells, and on understanding the necessary materials and interface properties. The final objectives are to synthesize beyond state of the art tandem and micro-concentrator solar cells using cost-effective materials. The research will be supported by training to place it in the broader context of other high efficiency ideas such as intermediate band, and hot carrier solar cells. It will consist of workshops by international experts, placements, a retreat, and organization of an international workshop. All of these objectives will be met by combining the expertise of the photovoltaic scientists of the University of Luxembourg, the materials and characterization scientists of the Luxembourg Institute of Science and Technology, and the external international scientists and companies involved.