Charge-generation structures and their applications in light-emitting devices

Due to their unique properties, charge-generation layers (CGLs) have been used as interconnect layers for organic and quantum-dot light-emitting devices (LEDs) consisting of multiple emission units. Furthermore, CGLs have also been integrated into single-emission-unit LEDs and alternating-current LEDs. The charge-generation structures provide charge carriers (electrons and holes) to the devices under an external electric field, instead of charge injection from the electrodes. Therefore, there is no strict requirement for precise matching of energy levels between the electrodes and charge-injection layers. This affords greater flexibility for device design and enhances the efficiency and operational lifespan of devices. In this review, we summarize the development of charge-generation structures and discuss the existing challenges and opportunities. A particular focus is placed on the working mechanism of CGLs and their applications in various LEDs. Additionally, issues such as voltage drop in CGLs, charge generation efficiency, increased operating voltage for the devices, and optimizations of existing CGLs are discussed.