Giant enhancement of photoluminescence emission in band-engineered type I TMDC/PbI₂ heterostructure by nonradiative energy transfer

Monolayer transition metal dichalcogenides (TMDCs) display the robust nature of excitonic or trionic photoluminescence (PL) emission due to direct bandgap nature, which can be enhanced by changes in the environment and the chemical potential of the material. However, a drastic PL quenching has been observed when TMDCs are stacked in van der Waals heterostructures and forming type II band alignment, which favors the nonradiative recombination of photocarriers. Herein, we have achieved an enhancement of the photoluminescence of monolayer MoS2 (and MoSe2) on top of a few layers PbI2 (forming van der Waals heterostructures) at resonance conditions in a room temperature regime. TMDC/PbI2 forms type I band alignment, which preserves light emission of MoS2 against nonradiative interlayer recombination processes. TMD monolayer can be enhanced by a factor of ~ 30 depending on the excitation wavelength. We have observed the enhancement of trion ~ 20 times compared to the monolayer TMDCs. Charge transfer and energy transfer both play crucial roles in the enhancement process. Furthermore, interlayer dipole coupling induced nonradiative Fo¨rster resonance energy transfer (FRET) process could be the possible reason of having such high enhancement of emission from TMDCs. Therefore, the present results of type I van der Waals heterostructures are highly promising materials for ultralight and ultrathin optoelectronics applications.