Enhancing the Photovoltage of Polymer Solar Cells by Using a Modified Cathode

A method to increase the open-circuit voltage (Voc) up to 200 mV and the power conversion efficiency (PCE) by 50%, by using a thin layer of poly(ethylene oxide) (PEO) to modify the cathode in polymer solar cells, was reported. An enhanced photocurrent of polymer solar cells by bending a small amount of PEO and LiCF3SO3 into the active layer was also demonstrated. The results show that the value of open-circuit voltage increases in all diodes with PEO by 150 to 200 mV while the fill factor (FF) increases with a decrease of the thickness of PEO. The thickness of the PEO layers on Si wafers measured by using ellipsometry shows that the thickness are 3.8 nm for 1000 rmp, 2.1 nm for 3000 rmp, and 1.4 nm for 5000 rmp. The quantitative similarity of the J-V characteristics in the dark between the diodes containing PEO and LiF shows that PEO has an analogous function in the device as LiF.