Progress on material, structure and function for tandem organic light-emitting diodes

Tandem organic light-emitting diodes (TOLEDs) generally consist of two or more electroluminescent (EL) units connected electrically in series via an intermediate layer. It has been found that the current efficiency of TOLEDs is potentially several folds higher than that of single EL unit device. Based on the latest great research efforts, herein we aim to present an overview of primary principles and designation for both efficient EL unit and intermediate layer in the aspects of functional materials, energy level, device architecture and optical properties. Moreover, the design of monochromatic, white and color tunable TOLEDs, is also presented to guide the precise regulation of charge carriers in the intermediate layer and exciton distribution in distinct EL units. Finally, we end this work by presenting the challenges of TOLEDs to achieve the appealing commercial interest for information display and solid-lighting source. It can be anticipated that novel functional materials and structural construction can be devised upon suitable device engineering to achieve high performance TOLEDs. (C) 2017 Elsevier B.V. All rights reserved.