Effect of PEDOT:PSS/metal electrodes on the performance of heterojunction solar cells

The properties of photovoltaic donor/acceptor blend organic solar cells are highly influenced by several parameters, such as the thickness of the active layers, the morphology of the film due to the solvent, the mobility of the free charge carriers and the electrodes used. In this work, the open-circuit voltage (Voc) of solar cells based on series of conjugated MDMO: PPV as donor and MCPM as acceptor were measured and compared. In each cell, the donor polymer was blended with an electron acceptor fullerene molecule with a ratio 1:4 (by weight). The devices were constructed in a sandwich structure with indium tin oxide ITO/metallic polymer as an anode, PEDOT: PSS acting as an anode and Al acting as a cathode. The values of Voc of the solar cells with indium tin oxide ITO/metallic polymer anode were compared against those for PEDOT: PSS acting as an anode. The Voc was found to be 1.0 V, and 0.7 V for the device with ITO and PEDOT: PSS as anodes, respectively. This 0.3V drop is attributed to the ohmic contacts at the interfaces resulting in band bending. The band bending created by accumulated charges at the ohmic contact produces a considerable loss in Voc of 0.3 V at room temperature.