  The coherent many-body interaction at the organic-inorganic interface can
give rise to intriguing hybrid excitons that combine the advantages of the
Wannier-Mott and Frenkel excitons simultaneously. Unlike the 2D inorganic
heterostructures that suffer from moment mismatch, the hybrid excitons formed
at the organic-inorganic interface have a momentum-direct nature, which have
yet to be explored. Here, we report hybrid excitons at the copper
phthalocyanine/molybdenum diselenide (CuPc/MoSe2) interface with strong
molecular orientation dependence using low-temperature photoluminescence
spectroscopy. The new emission peaks observed in the CuPc/MoSe2 heterostructure
indicate the formation of interfacial hybrid excitons. The density functional
theory (DFT) calculation confirms the strong hybridization between the lowest
unoccupied molecular orbital (LUMO) of CuPc and the conduction band minimum
(CBM) of MoSe2, suggesting that the hybrid excitons consist of electrons
extended in both layers and holes confined in individual layers. The
temperature-dependent measurements show that the hybrid excitons can gain the
signatures of the Frenkel excitons of CuPc and the Wannier-Mott excitons of
MoSe2 simultaneously. The out-of-plane molecular orientation is used to tailor
the interfacial hybrid exciton states. Our results reveal the hybrid excitons
at the CuPc/MoSe2 interface with tunability by molecular orientation, which
suggests that the emerging organic-inorganic heterostructure can be a promising
platform for many-body exciton physics.
