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.

串联有机发光二极管（TOLED）通常由两个或多个经由中间层串联电连接的电致发光（EL）单元组成。已经发现，TOLED的电流效率可能比单个EL单元器件的电流效率高几倍。基于最新的重大研究成果，本文旨在在功能材料，能级，器件结构和光学特性方面概述高效EL单元和中间层的主要原理和名称。此外，还提出了单色，白色和彩色可调谐TOLED的设计，以指导中间层中电荷载流子的精确调节以及不同EL单元中激子的分布。最后，我们通过提出TOLED的挑战来结束这项工作，以实现对信息显示和固态照明光源的吸引人的商业兴趣。可以预见，可以在适当的设备工程上设计出新颖的功能材料和结构构造，以实现高性能的TOLED。