Temperature- and Power-Dependent Characteristics of Heterointerlayer Excitons Emitting in the Visible Region of a WS2/PbI2 Nanostructure: Implications in Excitonic Devices

Heterointerlayer excitons (HIXs) have been intensively studied in heterostructures of various two-dimensional (2D) nanosystems with staggered band alignment (type II). In this study, the laser confocal microscopy (LCM) photoluminescence (PL) characteristics of exciton species, including HIXs in monolayer (1 L) WS2 and multilayer PbI2 heterostructures, were investigated from 3 to 293 K. The drastic decrease in the PL intensity of 1 L WS2 after hybridization with multilayer PbI2 indicates the occurrence of charge transfer. PL peaks corresponding to the neutral excitons (X0), trions (X–), and biexcitons (XX) of 1 L WS2 (i.e., intralayer excitons) were observed in the heterostructure at 3 K at 594, 601, and 606 nm in the deconvoluted PL spectra, respectively. Notably, a broad and intense PL emission mainly due to HIXs in the heterostructure was observed in the visible-light region at 675–700 nm (below 200 K). All of the PL peaks corresponding to the characteristic excitons in the heterostructure were red-shifted with increasing temperature owing to the enhancement of electron–phonon interactions. Interestingly, with increasing excitation power, the PL peaks of HIXs in the heterostructure were significantly blue-shifted, while those corresponding to the X0, X–, and XX of WS2 were red-shifted. These changes originate from the screening effect of the Coulomb and repulsive interactions between the dipole-aligned HIXs. Notably, the 4.22 ns lifetime of HIXs in the heterostructure obtained from the time-resolved PL decay curves at 3 K was significantly long and 8.6 times longer than that of the intralayer excitons. This study provides an understanding of HIXs in 2D heterostructures, which provide promising platforms for applications in nanoscale light-emitting diodes, sensors, and photovoltaics.