Charge Recombination in Phosphorescent Organic Light-Emitting Diode Host-Guest Systems through QM/MM Simulations

Host-guest systems are crucial for achieving high efficiency in most organic light-emitting diode (OLED) devices. However, charge recombination in such systems is poorly understood due to complicated molecular environment, making the rational design of host-guest systems difficult. In this article, we present a computational study of a phosphorescent OLED with 2,8-bis(triphenylsilyl)-dibenzofuran (BTDF) as the host and fac-tris(2-phenylpyridine) iridium (fac-Ir(ppy)(3)) as the guest, using a combined quantum mechanics/molecular mechanics (QM/MM) scheme. A new reaction coordinate is introduced to measure the electrostatic interactions between the host and guest molecules. Ionization potentials and electron affinities of the host show broader distributions as the host-guest interaction increases. On the basis of these distributions, we describe a molecular picture of charge recombination on the guest and find a direct charge trapping route for this system. Our results suggest several strategies for the design of more efficient host and guest combinations.