Near-Unity efficiency energy transfer from colloidal quantum wells of CdSe/CdS nanoplatelets to a monolayer of MoS2
Utilization of the energy transfer between different molecules has proven to be highly promising candidate for semiconductor nanocrystal optoelectronics including highly efficient light generation and harvesting in colloidal systems. This can be performed via transferring of the excitation energy from one molecule (i.e., donor) to another one (i.e., acceptor) through the near-field dipole – dipole coupling mechanism known as Förster resonance energy transfer (FRET). In this way, controlling the electron-hole pairs (excitons) flow in such a hybrid at nanoscale, will introduce novel and unique opportunities for having desired excitonic optoelectronics devices. The efficiency of FRET essentially depends on the absorption cross section of the acceptor and the distance between the donor and acceptor in donor–acceptor pair, the so-called Förster radius where the FRET efficiency becomes 50%. In addition, up to now it has been argued that FRET has a distance scaling which only depends on the geometry of the acceptor.
In a recent published study in ACS Nano, the team of researchers led by Prof. Hilmi Volkan Demir from Bilkent University – UNAM has shown near-unity efficiency (up to 99.88%) of FRET from the solid thin films of colloidal quantum wells of 4-monolayer CdSe/CdS nanoplatelets (NPLs) to a monolayer of MoS2 reaching an ultrafast FRET rate of 268.06 ns-1. Furthermore, atomically flat structure of the CdSe/CdS NPLs- donor and a monolayer of MoS2– acceptor, resulting in very strong layer-to-layer dipole – dipole coupling which enhances the near field Coulombic interaction in this system, allowing for reaching the longest Förster radius up to date ( 33 nm). According to the first author of this work, Nima Taghipour, due to the delocalization of the excitons in the layer of NPLs and consequently distributed of electric field in MoS2 layer, the rate of FRET follows d-2 distance scaling, however for two-dimensional acceptor as in here, one would expect that the FRET decays as d-4. Then, the results revealed that the geometry of the donor in such a hybrid system play a major role in modifying the decay kinetics. Professor Demir emphasized that the present study fills an important gap in understanding the behaviour of FRET for different dimensionalities of the donors and acceptors. The study has been published in ACS Nano. The full text can accessed from here: https://pubs.acs.org/doi/abs/10.1021/acsnano.8b04119