Origin of the enhanced open-circuit voltage in polymer solar cells via interfacial modification using conjugated polyelectrolytes

It has been previously shown that incorporating alcohol/water-soluble conjugated polyelectrolytes (CPEs) as cathode interlayers can substantially enhance the open-circuit voltage (V-oc) of bulk heterojunction polymer solar cells (PSCs). This improvement is attractive since there are only a few solution-based processing technologies that can enhance the V-oc. In this article, the V-oc enhancement effect of five distinct CPE materials was studied on three typical PSC device configurations, each using different donor materials. Significant V-oc enhancement was observed in devices that contain a polyfluorene copolymer as the donor material. The origin of the V-oc enhancement was investigated by examination of the dark currents.