Saulius Grigalevicius

Kaunas University of Technology, Lithuania

Title: Benzophenone-(Benzo)Carbazole-Based Host Materials for Efficient Red Phosphorescent OLEDs

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Biography

Saulius Grigalevicius received his B.S. degree in Chemical engineering, M.S. degree in Polymer chemistry and Ph.D. degree in Chemistry from Kaunas University of Technology (KTU), Lithuania, in June 1994, June 1996 and December 2000, respectively. From 2007 to 2008, he served as a Senior Researcher and an Associate Professor at KTU. From 2008 to 2010, he worked as a Leading Researcher and an Associate Professor at KTU. Since 2010, he has been working as a Professor and a Leading Researcher at the Faculty of Chemical Technology, KTU, Lithuania.

Abstract

Organic light-emitting diodes (OLEDs) have rapidly gained widespread commercial adoption; however, efficiency losses and stability issues remain persistent challenges, particularly for long-wavelength emitters. We have designed and synthesized four new benzophenone-(benzo)carbazole-based host materials, namely BP-Cz2, BP-BCz2, BP-BCz, and BP-CzBCz, incorporating carbazole and extended ?-conjugated benzo[a]carbazole electron-donating units, either individually or in combination. The compounds exhibited excellent thermal stability and formed stable amorphous thin films, with glass transition temperatures exceeding 100 °C. Photophysical characterization revealed singlet energy levels ranging from 2.90 to 3.61 eV and triplet energy levels between 2.50 and 3.10 eV, corresponding to singlet–triplet energy gaps of 0.35–0.51 eV. These energy characteristics confirm that the benzophenone derivatives provide sufficient exciton confinement for red phosphorescent emitters. Furthermore, charge-transport measurements indicated hole and electron mobilities spanning from 10?³ to 10?¹² cm²/Vs, highlighting the tunability of charge-transport properties through molecular design. The compounds were evaluated as host materials in red OLEDs. Notably, devices employing a co-host configuration consistently outperformed their single-host counterparts. In particular, the BP-BCz-based co-host system utilizing OLED achieved a maximum efficiency of 17.9% with reduced efficiency roll-off at high luminance. These results underscore the critical role of molecular asymmetry in improving charge balance and exciton confinement, demonstrating that rational host design, when combined with an appropriate co-host strategy, enables simultaneous optimization of carrier transport, suppression of exciton quenching, and stabilization of device performance under high-brightness operation, ultimately leading to highly efficient red phosphorescent OLEDs. This work was supported by the Research Council of Lithuania (Grant No. S-MIP-25-23).