Taking as a device model ITO|TPD|Alq 3 |Al (where TPD is N,N'-bis(3-methylphenyl)-N,N'-diphenyl-1,1'biphenyl-4,4'-diamine and Alq 3 is tris(quinolin-8-olato)aluminium) it is shown that control and improvement of carrier injection may be achieved using self-assembled monolayers (SAMs) to manipulate the Schottky energy barrier at the ITO±TPD interface. By using polar adsorbate molecules with the dipole oriented outward from the surface an arti®cial dipolar layer is formed and the work function is increased, and vice versa. With this method the threshold voltage for light emission (turn-on) can be reduced by 4 V and the maximum luminance increased by a factor of 3.5, giving an overall performance superior to that using the more stable Ag/Mg counter electrode. The SAMs effect is con®rmed using a Scanning Kelvin Probe (SKP) to pro®le the relative work function of half-coated ITO samples. Increases in work function in excess of 0.3 eV are observed, in line with predictions using the calculated molecular dipoles of the SAM molecules.