Improvement of the efficiency of CuPc/C60-based photovoltaic cells using a multistepped structure

Organic photovoltaic cells with multistepped (MS) structures based on a CuPc/C60 materials system were fabricated. A detailed analysis of the effect of stepped distributions on the device’s performance suggests that the highest efficiency is reached when the concentration gradient of donor and acceptor is largest. In this kind of device, owing to a great chemical potential energy gradient in addition to a large charge-separation (CS) interface, both the open-circuit voltage and short-circuit current density are improved remarkably, leading to a power conversion efficiency nearly one level higher than that of the bilayer device and 50% greater than the 1:1 homogeneously mixed device.