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

We investigate the electron-injecting properties of a ZnO substrate modified by a thin layer of solution-processed Cs(2)CO(3) into poly(9,9'-dioctylfluorene)-co-benzothiodiazole (F8BT). Ultraviolet photoemission spectroscopy studies reveal that in the case of coannealed F8BT/Cs(2)CO(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(2)CO(3) in the coannealed F8BT/Cs(2)CO(3) films. I-V measurements in single carrier devices show a significant improvement in the electron injection of the coannealed F8BT/Cs(2)CO(3), in agreement with the observed n-doping of the polymer upon coannealing. (C) 2011 American Institute of Physics. [doi:10.1063/1.3564903]