Enhancement in open circuit voltage through a cascade-type energy band structure

In this paper, we report a method to increase the open-circuit voltage (V-OC) of an organic solar cell by inserting an interfacial layer between the donor and acceptor layers to form a cascade-type energy band structure. We demonstrate its feasibility using a recently reported asymmetric pentacene derivative, tetraceno[2,3-b]thiophene (TT) as a donor material, C-60 as an acceptor material, and copper phthalocyanine (CuPc) as the sandwich layer. The V-OC was increased from 0.3 V for the device with no CuPc sandwich layer to 0.56 V for 13 nm thick CuPc layer. The power conversion efficiency (PCE) of the device with 13 nm CuPc layer was 1.53% and the fill factor (FF) was 0.64, in comparison to TT/C-60 device which had a PCE of 0.78% and a FF of 0.52. (C) 2007 American Institute of Physics.