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Block copolymer (BCP) based polymer solar cells are potentially more stable than blend based systems as they have a distinct equilibrium nanostructure, which is determined by the polymer architecture and the block interactions. BCPs could be used to produce organic solar cells with consistent efficiency and device properties, largely unaffected by the choice of processing conditions. On page 1705, Chao Yan et al. study a triblock copolymer of PFM-F8BT-PFM using structural (grazing incidence scattering, as seen on the cover) and optical characterization techniques. The BCP has a device efficiency three times that of the blend. However the optical measurements show that the BCP exhibits exciplex emission and that the triplet yield is twenty times that of the blend. Both of these factors severely limit the device efficiency, but the potential of BCP based solar cells is clearly demonstrated.