Plausible degradation mechanisms in organic light-emitting diodes

Organic light emitting diode has become a highly attractive technology for high quality displays and lighting. These applications, however, strongly rely on their lifetime. Probing all the possible failure mechanisms has hence become crucial. We reveal here that the device lifespan depends on the dielectric strength, internal electric field, morphology, thermal stability, and migration of the composing organic and inorganic materials as well as span of recombination zone and device efficiency. Additionally, the lifetime is highly sensitive to the thickness of electron transporting layer. By taking a green emitter doped in 4,4-bis(carbazol-9-yl)biphenyl host for example, the device lifetime can be increased from 51 to 209 h at 1000 cd/m2, an increment of 310%, and its efficacy increased from 21 to 41 lm/W, an increment of 96%, as the thickness is increased from 20 to 40 nm. The results show high device reliability to be achievable provided it composes materials with high dielectric strength, high glass transition property and low migration tendency, and uniform layered structure with low built-in internal electric field, wide recombination zone and high efficiency.