Improved electron injection in poly(9,9' -dioctylfluorene)-co-benzothiodiazole via cesium carbonate by means of coannealing

摘要

We investigate the electron-injecting properties of a ZnO substrate modified by a thin layer of solution-processed Cs_2CO_3 into poly(9,9'-dioctylfluorene)-co-benzothiodiazole (F8BT). Ultraviolet photoemission spectroscopy studies reveal that in the case of coannealed F8BT/Cs_2CO_3 films, the Fermi level is pinned at the lowest unoccupied molecular orbital of the F8BT, indicating significant n-doping of the polymer. X-ray photoemission spectroscopy measurements reveal the presence of Cs_2CO_3 in the coannealed F8BT/Cs_2CO_3 films. Ⅰ-Ⅴ measurements in single carrier devices show a significant improvement in the electron injection of the coannealed F8BT/Cs_2CO_3, in agreement with the observed n-doping of the polymer upon coannealing.