Ned’s research aims to fundamentally increase the efficiency of photovoltaic solar cells towards the ultimate efficiency limit for solar power conversion of 87%. This research begins by establishing conceptual thermodynamic boundaries of the processes that can (and cannot) lead to efficiency improvements in solar cells. This is followed by practical work to demonstrate working, proof-of-principle devices and often involves computer modelling, optical spectroscopy in addition to standard photovoltaic device measurements. Several 'Advanced Concept' devices have emerged from this work, notably the quantum well solar cell that enabled a 32.9% III-V double junction solar cells to be made, photo-molecular up-conversion on amorphous silicon solar cells, photon ratchet sequential absorption photovoltaic device and several demonstrations of a hot carrier solar cell.