Indolo[3,2,1-jk]carbazole based planarized CBP derivatives as host materials for PhOLEDs with low efficiency roll-off

• Planarization strategy towards CPB based materials applied.
• Significantly improved thermal stabilities and triplet energies observed.
• Green and blue PhOLED devices with low efficiency roll-off fabricated.
• Blue PhOLEDs with high PE of 26.1 lm W−1 realized.
• Indolo[3,2,1-jk]carbazole as building block for organic electronics established.

Three novel planarized CPB derivatives (ICzCz, ICzPCz, ICzICz) have been synthesized and characterized concerning applications as host materials for PhOLEDs. The incorporation of fully planar indolo[3,2,1-jk]carbazole (ICz) in the CBP scaffold has been systematically investigated, revealing a significant impact on molecular properties, such as improved thermal stability (tg > 110 °C), high triplet energies (ET > 2.81 eV) and charge transport properties. Employing the newly developed materials as host materials, efficient green PhOLEDs (CEmax: 60.1 cd A−1, PEmax: 42.1 lm W−1, EQEmax: 15.9%) with a remarkably low efficiency roll-off of 5% at 1000 cd m−2 as well as blue PhOLEDs (ICzCz) with a high PE of 26.1 lm W−1 have been realized. Hence, the first comprehensive report on the application of ICz as integral building block for electroluminescent materials is presented, establishing this particular structural motive as versatile structural motive in this field.

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