Work function reduction using 8-hydroxyquinolinolato-lithium for efficient inverted devices

The work function reduction of various transparent conducting materials with 8-hydroxyquinolinolato-lithium (Liq) was investigated using in situ ultraviolet photoelectron spectroscopy (UPS) measurements. The work function of single-walled carbon nanotubes (SWCNTs), poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), and indium tin oxide (ITO), was significantly reduced by 1.00, 1.08 and 0.50 eV by depositing a 3.5 nm-thick Liq layer. This originates from the interface dipole having its negative pole pointed toward each electrode. These work function reductions would enhance electron injection or extraction in inverted organic electronic devices. However, the high electron injection barriers from electrodes to Liq itself were observed (2.43-2.53 eV), and thus an ultrathin Liq layer should be used for efficient electron injection through tunneling mechanism.