Progress in organic semiconducting materials with high thermal stability for organic light‐emitting devices

Organic light‐emitting devices (OLEDs) have been extensively studied over the past three decades and are still attracting attention owing to their potential use in flexible and foldable displays. To achieve highly durable OLED displays for flexible devices, constitutive OLED materials need to be stable in various environments, including those with thermally and mechanically severe conditions. To this end, the present review aims to investigate the progress of OLED material research over the past two decades with respect to thermal stability. The literature survey is first conducted using the keyword “OLEDs” and then narrowed down to “high thermal stability materials for OLEDs.” The number of search results indicates that creating OLED materials with high thermal stability is a widely studied topic in the field of OLED research and has undergone an average growth rate of approximately 15% per year over the past two decades. In this review, the OLED materials used as core layers (ie, the hole injection and transport layers, emission layers, and electron injection and transport layers) are thoroughly analyzed, and the best representative materials are discussed in detail by summarizing their major thermal and electronic characteristics. Finally, several previous reports on flexible and foldable OLED displays are analyzed to determine the importance of the stability of their constitutive materials. As the paradigm of mobile devices shifts toward foldable and wearable electronics, OLED displays need further advances by achieving better durability and functionality. This review discloses that the thermal stability of OLED materials has been gradually improved irrespective of their applications layers, even though further advances in OLED materials are necessary for flexible displays with very high durability.