Effect of metal electrodes on the performance of polymer:fullerene bulk heterojunction solar cells

An increase in the workfunction of the metal top electrode leads to a reduction of the open-circuit voltage, short-circuit current, and power conversion efficiency of organic bulk-heterojunction solar cells. It has been demonstrated that the photocurrent obtained from an active layer comprised of a blend of poly(2-methoxy-5-(3('),7(')-dimethyloctyloxy)-p-phenylene vinylene) (OC1C10-PPV) and [6,6]-phenyl C-61-butyric acid methyl ester (PCBM), with lithium fluoride topped aluminum, silver, gold, or palladium electrodes, shows a universal behavior when scaled against the effective voltage across the device. Indeed, model calculations confirm that the dependence of the photocurrent on the effective voltage is responsible for the observed variation in performance of each different electrode. Consequently, for any given metal, only the device's open-circuit voltage is required in order to be able to predict the remaining solar cell parameters. (C) 2004 American Institute of Physics.