Structure Dependent Properties of 2D Organic Crystals on MoS₂

2D layered materials have attracted significant scientific attention, as their 2D nature allows the stacking of different materials leading to a control of functionality. Combining 2D-like layers of organic molecules with inorganic 2D materials offers even more tuning possibilities. However, a detailed understanding of the properties of such heterostructures is still lacking.

The organic molecules perylenetetracarboxylic dianhydride (PTCDA) and perylenetetracarboxylic diimide (PTCDI) are similar in atomic structure and composition (the main difference being the end groups), but give rise to a different density of states when deposited on monolayer MoS₂. To understand this experimental observation, we performed an in-depth investigation of these molecules using density functional theory [1]. We find that the highest occupied and the lowest unoccupied molecular orbitals split in energy for PTCDI when forming the monolayer structure. PTCDA does not have this splitting. We show that the splitting is related to the stacking of the molecules in the monolayer, and not due to the chemical structure of the molecules.

[1] K. Rijal, S. Amos, P. Valencia-Acuna, F. Rudayni, N. Fuller, H. Zhao, H. Peelaers, and W.-L. Chan, Nanoscale Periodic Trapping Sites for Interlayer Excitons Built by Deformable Molecular Crystal on 2D Crystal, ACS Nano 17, 7775 (2023).