Multi-layer encapsulation structures for stable bottom- and top-emitting white OLED devices

Abstract

Organic light-emitting diode (OLED) devices have problems such as poor environmental stability, low thermal tolerance, and decomposition of materials. This work focuses on the encapsulation of white OLED devices with bottom and top emission. White OLED devices are realized by stacking tricolor luminescent materials as the light-emitting layer. The encapsulation structure is constructed with heat-conductive films, an inorganic barrier layer, liquid transparent glues, a POSS resin coating, and transparent films and glasses to solve stability problems. A three-dimensional protection system is constructed by multi-layer encapsulation, which consists of environmental isolation, a stress buffer, and thermal management. In addition, the highlight transmittance in either the bottom- or top-emitting directions is guaranteed by multiple transparent materials during encapsulation. The fabricated devices show white-light emission with an external quantum efficiency (EQE) of 11.6% for the top-emitting device and 7.5% for the bottom-emitting device. The decays of the encapsulated devices are significantly lower than those of unencapsulated devices, indicating that the designed encapsulation structures can improve the stability of the OLED devices. After 720 h, the encapsulated top- and bottom-emitting devices show a decay of about 20% and 16%, respectively. In contrast, the bright decay of the unencapsulated device exceeds 40%.