The rapid rise in performance of organic solar cells over the last decade derived in large part from advances in materials chemistry and processing morphology control of the donor–acceptor photoactive active layers. As a consequence, much of the work in device physics of organic solar cells has focused on the fundamental limits imposed by the photoactive layer, assuming that contacts are non-limiting through the use of MoOx and ZnO2 as hole- and electron-collection layers, with sufficiently high  and low work functions, respectively. However, even so, contacts still do limit the performance of organic solar cells.