Stability of polymer light-emitting diodes

In this paper, we report on the lifetime of polymer LEDs fabricated at Phil ips Research. For single-layer LEDS, we find thar the operational lifetime in nitrogen gas is limited by the stability of the indium-tin-oxide (ITO) a node. By using a polymeric capping layer for the ITO, we obtain more stable devices. In air, the lifetime is limited by black spot formation. Small pi nholes in the cathode layer are the origins of the black spots. Water or ox ygen may diffuse through these pinholes and react with the cathode, causing degradation. By encapsulating the devices we can prevent black spot format ion. Our present 8 cm(2) devices have lifetimes of many thousands of hours at daylight visibility under ambient conditions.