Enhanced performance of polymer solar cells with imprinted nanostructures on the active layer

Different nanoimprint techniques are adopted to make nanostructures on the active layer of a conjugate polymer solar cell to improve light trapping in order to improve the solar cell performance. The active layer is a conductive polymer blended with fullerene, which becomes very sticky and difficult to imprint with traditional hard mold or hard mold coated with anti-adhesion materials. Therefore, soft mold such as polydimethylsiloxane having low surface energy is made, which can imprint the surface of the active layer and increase the light absorption. Problems encountered with different imprint techniques will be discussed. A small imprint machine is developed to imprint the nanostructures on the active layer without contact with air and moisture. Nanostructures with either random or regular arrays are made to texture the active layer and increase the cell performance. However, light trapping and charge transport and collection should be compromised in order to achieve a much higher cell performance. The current and voltage characteristics of the textured solar cells are measured which indicate that the short circuit current density can increase from 8.61 to 9.61 mA/cm2, the fill factor from 0.452 to 0.580. The cell performance of the textured solar cells increases from 2.3% to 3.29%, which represents an increase of 43%.