Charge-Transfer-Induced Photoluminescence Properties of WSe2 Monolayer–Bilayer Homojunction

The charge-transfer process in transition-metal dichalcogenides (TMDCs) lateral homojunction affects the electron–hole recombination process of in optoelectronic devices. However, the optical properties of the homojunction reflecting the charge-transfer process has not been observed and studied. In this work, we investigated the charge-transfer-induced emission properties based on monolayer (1L)–bilayer (2L) WSe2 lateral homojunction with dozens of nanometer monolayer region. On the one hand, the photoluminescence (PL) emission of bilayer WSe2 from the homojunction area blue shifts ∼23 and ∼31 meV for direct and indirect bandgap emission, respectively, compared with the bare WSe2 bilayer region. The blue shift of the emission spectrum in the bilayer WSe2 is ascribed to the decrease in binding energy induced by charge transfer from monolayer to bilayer. On the other hand, the energy shift shows a tendency to increase as the temperature decreases. The energy blue shift is ∼57 meV for direct bandgap emission at 80 K, which is larger than that (∼23 meV) at room temperature. The larger-energy blue shift at low temperature is derived from the larger driving force under larger band offset. Our observations of the unique optical properties induced by efficient charge transfer are very helpful for exploring novel TMDC-based optoelectronic devices.