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 (T-g), 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 (L: 13 955 cd m(-2), eta(ex): 4.90%, eta(c): 6.0 cd A(-1), and eta(p): 5.4 lm W-1) 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 (L: 13 856 cd m(-2), eta(ex): 4.70%, eta(c): 5.7 cd A(-1), and eta(p): 5.2 lm W-1). 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)(3) exhibited the maximum L of 8891 cd m(-2), eta(ex) of 19.3%, eta(c) of 27.9 cd A(-1) and eta(p) of 33.4 lm W-1 with CIE coordinates of (0.31, 0.60) and the red device based on Cz-DEPVI: Ir(MQ)(2)(acac) exhibited the maximum L of 40 565 cd m(-2), eta(ex) of 19.9%, eta(c) of 26.0 cd A(-1) and eta(p) of 27.0 lm W-1 with CIE coordinates of (0.64, 0.37).