Recent advances in thermally activated delayed fluorescence for white OLEDs applications

Abstract

Thermally activated delayed fluorescence (TADF) materials, which can harvest all excitons without utilizing any noble metals to emit light, are becoming the key cornerstone for developing the next generation of organic light-emitting diode (OLED) devices. In recent years, TADF materials are attracting numerous attentions as a new surge of research focuses on both science and industry owing to their high efficiency, low power consumption, and low production cost attributes when applied to white OLEDs. The design and application of TADF in WOLED devices have also experienced the rapid development in fundamental science and industrial technology perspectives. In the present review, the specific reverse intersystem crossing mechanism and evolution of TADF is outlined firstly, and then the latest research progress of TADF-WOLEDs is summarized and discussed. TADF/conventional fluorescence, TADF/phosphorescence, all TADF and TADF exciplex-based WOLEDs are categorized and elaborated in terms of the device structure, working mechanism, efficiency, color-rendering index, etc. Finally, we conclude with the future challenges and opportunities in high-quality TADF devices and application area.

Theoretical Characterizations of TADF Materials: Roles of ΔG and the Singlet–Triplet Excited States Interconversion

“…Thermally activated delayed fluorescence (TADF) materials have attracted increasing attention for organic light-emitting diodes (OLEDs) because of their ability to harness all of the electrogenerated triplet and singlet excitons for fluorescence. − Deep understanding of the TADF mechanism and the establishment of good descriptors are very important for the molecular design of highly efficient TADF materials. − In the TADF process of organic molecules, the triplet exciton first goes uphill to the singlet excited state through reverse intersystem crossing (rISC) and then emits fluorescence. Therefore, the rISC process is key to the occurrence of the TADF phenomenon.…”

Dispositivos emisores de luz basados en compuestos semiconductores orgánicos: una revisión aplicada a emisores rojos

“…Figura 2. Estructura dispositivo OLED Las moléculas que retornan al estado son solo el 25 % del total en estado excitado y solo esa fracción de excitones contribuye a la emisión (Xue et al, 2020), ya que el restante 75 % se considera perdido para emisión por regla de selección cuántica de espín ( ), que prohíbe las transiciones del estado singlete al estado triplete y viceversa. Por tanto, la IQE (acrónimo de Internal Quantum Efficiency) máxima posible solo puede ser del 25 % (Forrest, 2020).…”

“…Con este mecanismo de emisión se lograron los OLED de segunda generación (Pode, 2020) caracterizándose porque la IQE del dispositivo alcanza el 100 %, debido a que se aprovecha el otro 75 % de los excitones que no tenían permitida la emisión radiativa, por tanto, la emisión del OLED mejora al ser comparada con el mecanismo de fluorescencia (Baldo et al, 1998;Xue et al, 2020). Una de las particularidades que posee la fosforescencia es que se logra en compuestos que contienen átomos de Z grande como el iridio y las tierras raras, con los que se logra romper la prohibición cuántica.…”

Different electrode anodes used in OLED devices Diferentes eletrodos anodos usados em dispositivos OLEDs

“…Consequently, better performance is presented. This material is called hole transport layer (HTL), and a very used commercial material is known as poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) 33,34 ; • On the HTL the electroluminescent layer (EL) that promotes the electrical charges (holes and electrons) recombination to form the exciton (light emission) is deposited 35,36 . In the literature, several materials presenting different wavelengths have been found [37][38][39] ; • On the electroluminescent layer a thin film called as electron transport layer (ETL) is deposited.…”