Formation of bubbles on electrical contacts to polymer light-emitting diode devices

Bubble formation on calcium/aluminum contacts to bilayer poly(n-vinyl carbazole) (PVK)/poly(3,4-ethylenedioxythiophene)-poly(4-styrenesulfonate) (PEDOT-PSS) polymer light-emitting diode (PLED) devices was studied using optical and electron microscopies and Auger electron spectroscopy (AES). The formation of bubbles is shown to correlate with pinholes in the metal contact thin film and with excess absorbed water in the presence of the calcium layer. AES data show oxidation at the Ca/Al interface during this process. Gas evolution and relaxation of compressive stress when voltage is applied to the PLED devices are postulated to cause formation of the bubbles.