Enhancements in open circuit voltage, photocurrent (see figure), and fill factor are observed by inserting a thin poly(ethylene oxide) layer between a metal electrode (Al) and active layers in polymer solar cells based on a polyfluorene copolymer poly((2,7-(9-(2'-ethylhexyl)-9-hexyl-fluorene)-alt-5,5-(4',7'-di-2-thien yl-2',1',3'-benzothiadiazole))-co-(2,7-(9-(2'-ethylhexyl)-9-hexyl-fluorene) -alt- 2,5-thiophene))(APFO-5) and [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) under illumination of AM 1.5 (100 mWcm(-2)).