Highly Efficient Bipolar Host Materials towards Solution-Processable Blue and Green Thermally Activated Delayed Fluorescence Organic Light Emitting Diodes
Mallesham Godumala, Suna Choi, Seong Keun Kim, Si Woo Kim, Jang Hyuk Kwon, Min Ju Cho, Dong Hoon Choi
Journal of Materials Chemistry C
New versatile host materials with good solubility in common organic solvents are greatly desired to promote solution-processable thermally activated delayed fluorescence organic light-emitting diodes. This paper describes the design and synthesis of two new host materials, namely 3’-(9H-Carbazol-9-yl)-[1,1’-biphenyl]-3,5-diylbis(diphenylphosphine oxide) (CDPO) and 3’,5’-di-(9H-carbazol-9-yl)-[1,1’-biphenyl]-3,5-diylbis (diphenylphosphine oxide) (mCPDPO), featuring hole-affine carbazole and electron-affine diphenylphosphine oxide (DPO) entities. The donor strength was varied to a constant n-type DPO core to tune the functional properties. The detailed studies proved that the resulting two new materials exhibit excellent solubility in common organic solvents, high triplet energy (> 2.80 eV), high glass transition temperature (up to 133 °C), and good bipolar electronic nature. Consequently, both compounds were executed as hosts in solution-processable blue and green thermally activated delayed fluorescence (TADF) OLEDs. In particular, the devices using mCPDPO as a host in the emissive layer bestow outstanding performance with maximum current efficiency, power efficiency, and external quantum efficiency of 35.3 cd A−1, 17.0 lm W−1 and 15.4% in the blue-emitting diode, and 61.5 cd A−1, 29.7 lm W−1 and 18.8% in the green-emitting diode, respectively. These results corroborated the potential of carbazole-phosphine oxide derivatives as host materials in solution-processable blue and green TADF OLEDs.
Fluorescence, Photoluminescence, Solid state, Optical properties, Materials