  In this work we present a systematic study of three representative iridium
dyes, namely, Ir(ppy)3, FIrpic and PQIr, which are commonly used as sensitizers
in organic optoelectronic devices. We show that electronic correlations play a
crucial role in determining the excited-state energies in these systems, due to
localization of electrons on Ir d orbitals. Electronic localization is captured
by employing hybrid functionals within time-dependent density-functional theory
(TDDFT) and with Hubbard-model corrections within the delta-SCF approach. The
performance of both methods are studied comparatively and shown to be in good
agreement with experiment. The Hubbard-corrected functionals provide further
insight into the localization of electrons and on the charge-transfer character
of excited-states. The gained insight allows us to comment on envisioned
functionalization strategies to improve the performance of these systems.
Complementary discussions on the delta-SCF method are also presented in order
to fill some of the gaps in the literature.
