Excitons and Singlet Fission at the Crystalline Tetracene-Silicon Interface

Excitons in organic crystalline semiconductors play a crucial role in the operation of optoelectronic devices, such as organic solar cells, light-emitting diodes, and photodetectors. The excitonic properties of materials are dramatically affected by the presence of surfaces and interfaces. Using the GW method and Bethe-Salpeter equation, we investigate the influence of a neutral hydrogen-passivated 1 x 2 reconstructed (100) silicon substrate on excitons within the crystalline tetracene layer deposited on the top of it. Our findings reveal that singlet excitons in the contact tetracene layer are situated within the continuum of unbound Wannier-Mott excitonic states in silicon, with noteworthy hybridization between these states. Consequently, in the contact tetracene layer, all singlet excitons exhibit a pronounced interlayer charge transfer character, while the triplet exciton remains confined to the tetracene layer. This makes the singlet fission effect highly improbable for the contact tetracene layer. Additionally, the presence of the silicon substrate results in a modification of the singlet-triplet gap by 144 meV. This change is solely attributed to hybridization with excitons in silicon, which influences the exchange energy. Our results show that the dynamic dielectric screening caused by the substrate does not impact the singlet-triplet gap but alters the exciton binding energies. [GRAPHICS]