Efficient Tandem White OLED/LEC Hybrid Devices

Abstract

Organic light‐emitting diodes (OLEDs) attract much research attention owing to their superior device characteristics in display and lighting applications. However, multi‐layered organic thin films deposited by thermal evaporation in a high‐vacuum chamber complicate the fabrication processes and increase the production costs. Alternatively, solution‐processable single‐layered light‐emitting electrochemical cells (LECs) possess easy fabrication and good device performance due to in situ electrochemical doping. To take advantages of both types of devices, the study proposes an efficient tandem white OLED/LEC hybrid device by stacking a red OLED on top of a blue LEC with a sophisticatedly designed charge‐generating layer (CGL). The proposed tandem device exhibits a high external quantum efficiency (EQE) of 21.53%, which is almost the sum of the EQEs of the two stacked devices. When fabricated on the diffusive substrate to recycle the trapped light in the substrate, the EQE can be further enhanced to reach 37.88%. Besides connecting the two stacked devices, the CGL improves the carrier balance of the blue LEC due to enhanced electron injection. This study demonstrates that the white tandem OLED/LEC hybrid device has a simpler device structure than all‐vacuum‐processed tandem OLEDs but it still delivers high device efficiency, revealing its potential in lighting applications.