Efficient Full-colour Organic Light-emitting Diodes Based on Donor-acceptor Electroluminescent Materials with a Reduced Singlet-triplet Splitting Energy Gap

A series of efficient blue-emitting materials, namely, Cz-DPVI, Cz-DMPVI, Cz-DEPVI and TPA-DEPVI, possessing a donor-acceptor architecture with dual carrier transport properties and small singlet-triplet splitting is reported. These compounds exhibit excellent thermal properties with a very high glass-transition temperature ( ), and thus, a stable uniform thin film was formed during device fabrication. Among the weak donor compounds, specifically, Cz-DPVI, Cz-DMPVI and Cz-DEPVI, the Cz-DEPVI-based device showed the maximum efficiencies (: 13 955 cd m, : 4.90%, : 6.0 cd A, and : 5.4 lm W) with CIE coordinates of (0.15, 0.06) at 2.8 V. The electroluminescent efficiencies of Cz-DEPVI were higher than that of the strong donor TPA-DEPVI-based device (: 13 856 cd m, : 4.70%, : 5.7 cd A, and : 5.2 lm W). Furthermore, these blue emissive materials were used as hosts to construct efficient green and red phosphorescent OLEDs. The green device based on Cz-DEPVI:Ir(ppy) exhibited the maximum of 8891 cd m, of 19.3%, of 27.9 cd A and of 33.4 lm W with CIE coordinates of (0.31, 0.60) and the red device based on Cz-DEPVI:Ir(MQ)(acac) exhibited the maximum of 40 565 cd m, of 19.9%, of 26.0 cd A and of 27.0 lm W with CIE coordinates of (0.64, 0.37).