Exciton Dynamics in Janus WSSe Driven by Structural Asymmetry

Artificially engineered Janus transition metal dichalcogenides (TMDCs) feature distinct chalcogen atoms on their top and bottom layers that break mirror symmetry, which is expected to alter the exciton dynamics and exciton–phonon interactions. Here, we present direct experimental evidence of the dipolar nature of excitons in high-quality Janus WSSe monolayers. Spatial imaging of exciton emission reveals that the exciton diffusion length in Janus WSSe is almost twice that of WS₂, which is attributed to electron–hole spatial separation induced by the intrinsic out-of-plane electric field. Furthermore, temperature-dependent photoluminescence measurements indicate significantly enhanced excitonic line width broadening of WSSe above 100 K, arising from stronger exciton–phonon scattering via additional optical phonons. These findings highlight the pivotal role of intrinsic structural asymmetry in governing radiative and nonradiative processes in Janus TMDCs and offer insights into their potential for excitonic device applications.