Photovoltaic devices have a number of fundamental limitations that prevent an efficient use of all sunlight.These include the finite absorption range of the solar cells,thermalization loses and thermodynamic considerations,among other effects.Semiconductor quantum nanostructures pave the way of beating some of these limitations and achieving much higher conversion efficiencies.Multiple quantum wells and quantum dots are amongst the most widely studied nanostructures.Strain balanced quantum wells are a consolidated technology that has proven its potential in the past,and that might have the key for beating the efficiency barrier of 50% in the near future.Their main advantages are the possibility of tailoring the absorption of the host devices in monolithic,lattice matched multi-junction solar cells to better match the solar spectrum and to promote photon recycling and photonic coupling between subcells,therefore reducing radiative losses.In turn,quantum dots have been extensively used to explore more challenging approaches,but with the potential of achieving higher gains,too.The intermediate band solar cells,including the photon"ratchet"version developed recently at Imperial College London,multiple exciton generation or hot-carriers are the main application fields of these nanostructures with,still,several issues to solve.In this work,we summarise in what way these nanostructures can help to overcome these fundamental limitations,focussing on the work carried out recently at Imperial College London,and reviewing the main challenges that they have to face to reach the highest efficiencies.