The HEMP workshop series started in 2011 and tackles a range of topics associated with high- efficiency PV research. Each year has a principle topic, but the programme is not exclusive. In previous years HEMP themes have included the intermediate band solar cell, the hot carrier solar cell and the application of nano photonics in photovoltaics. HEMP 2015 will bring together researchers working on highly mismatched alloys for PV, bridging the gap between materials fabrication and characterisation, device design and theory on a multiscale level. Participants will present the state of the art results in their respective fields and share the difficulties they are facing, spot the missing information that is necessary in order to design efficient solar cells, and establish collaborative activity to achieve the next stage in the development of these materials for photovoltaic devices.