Photoluminescence and photoconductivity studies of oriented polyfluorene thin films

Photoluminescence and photoconductive properties of poly(9,9-dioctylfluorene) (F8) on rubbed polyimide (PI) alignment layers have been studied. The F8 thin films are highly oriented, which is manifested from polarized absorption, fluorescence, and photoconductivity spectra (the order parameter of F8 is 0.86). The ratio of photocurrent parallel to perpendicular directions to the rubbing direction (photoconductivity anisotropy) is 18 at 2.9 eV for F8. Effects of C60 addition to F8 on the optical properties are also studied. C60 addition to F8 significantly increases photoconductivity but decreases the order parameter (0.67) and the photoconductivity anisotropy (7 at 2.9 eV). Both F8 and C60 doped F8 thin films exhibit similar photoconductive response and similar photoconductivity anisotropy (3–4) above 3.8 eV.