Whilst inspiring significant academic interest, the maximum power conversion efficiencies achieved by polymer PVs under solar conditions (PCE; 6.10-6.77%), are not yet sufficient for the devices to become widely marketable. Therefore much current work in the area is focussed on raising device efficiencies as far as possible towards theoretically achievable levels. To this end, key strategies involve material design and synthesis, device processing, and methods for controlling the morphology of the active components. This review aims to highlight the importance of morphological design and control for highly efficient polymer PVs, to discuss strategies by which morphology can be controlled, and to outline some of the characterisation techniques vital to the understanding and optimisation of morphology in these materials. (C) 2010 Elsevier Ltd. All rights reserved.