Molecular engineering of indolocarbazole–silane hosts for blue phosphorescent organic light-emitting diodes with improved thermal stability and efficiency

This study reports the molecular engineering of indolocarbazole-based host materials incorporating triphenylsilane units for high-performance blue phosphorescent organic light-emitting diodes (PhOLEDs). Two novel host materials, DIINCz-Si and INCz-Si, were designed and synthesized to enhance thermal stability while maintaining high triplet energy levels and suitable frontier molecular orbital energies for efficient energy transfer and charge balance. The introduction of the triphenylsilane moiety increased the molecular rigidity and significantly improved the thermal decomposition temperature, with values reaching up to 427 °C. Both materials exhibited favorable photophysical and electrochemical properties, making them suitable hosts for blue phosphorescent emitters. Blue PhOLEDs fabricated using these hosts demonstrated excellent electroluminescent performance, achieving a maximum external quantum efficiency (EQE) of 22%, a current efficiency of 41 cd A⁻¹, and a power efficiency of 43 lm W⁻¹, together with a low turn-on voltage and reduced efficiency roll-off. These results indicate that incorporating silane groups into the indolocarbazole framework effectively enhances thermal stability, charge transport, and exciton confinement, leading to superior device performance. This work provides an effective molecular design strategy for developing thermally stable and highly efficient host materials for next-generation blue PhOLED applications.