Organic photovoltaics (OPVs) promise a low-cost alternative to traditional inorganic PV technology. Recently, the relatively poor efficiency of a bulk-heterojunction OPV has been improved considerably (> 10%) in a tandem cell configuration, albeit at the expense of using four different organic materials. In this work, we revive the concept of 'single-material tandem cells' - originally developed in the 1990s to address the transport bottleneck of a-Si solar cell. We demonstrate that OPV sub-cells made of the single polymer (or organic semiconductor) and arranged in a series tandem configuration can lead to impressive (factor of 2-5) efficiency gains, provided that the sub-cells can be thinned for optimum carrier collection and stacked for improved light absorption. Our analysis may open up a new direction in OPV research and a completely different design space for such tandem structures. (C) 2013 Elsevier B.V. All rights reserved.