We simultaneously surface-functionalize PbS nanocrystals with Cu 4,4′,4′′,4′′′-tetraaminophthalocyanine and assemble this hybrid material into macroscopic monolayers.

Research on two-dimensional (2D) atomic crystals is one of the highly progressive topics in (opto)electronics, as the van der Waals (vdW) interactions enable integration of 2D crystals with a broad range of materials. Organic π-conjugated molecules offer new opportunities for creating the so-called “hybrid” vdW heterostructures, in which their anisotropy adds an extra degree of functional possibilities. Moreover, it was found that in the case of organic molecules, the 2D substrate changes the molecular orientation, which in turn can enhance the overall optoelectronic properties. However, the reorientation of the molecules has been until now studied solely on the graphene underlayer that restrained its applicability to a broader range of materials. Here, we study the molecular orientation of diindenoperylene (DIP), a representative of rodlike organic semiconductors, on the MoS₂ monolayer. Our results show that DIP forms separate islands on the top of the MoS₂ monolayer with lying-down orientation of the molecules. We combine the grazing-incidence X-ray diffraction technique with atomistic simulations to reveal the exact molecular arrangement on the atomically thin underlayer. We also investigate optical absorption spectra for different thicknesses of the DIP layer, as they are of fundamental importance for various applications in organic-based optoelectronics.

We show that small π-conjugated molecules adopt a lying-down orientation when deposited on few-layer MoS ₂ with horizontally oriented layers. In contrast, for vertically aligned MoS ₂ layers, DIP molecules are arranged in a standing-up manner.