Interfacial Control of Hot-Carrier Extraction and Photostability in Two-Dimensional Materials

Two-dimensional transition metal dichalcogenides are promising materials for next-generation optoelectronic devices, yet their implementation is hindered by limited sample stability and challenges in forming reliable electrical contacts. Here we show that interface morphology critically governs the energy band alignment at TMDC-metal junctions, thereby determining their optoelectronic response and susceptibility to degradation. We probe the underlying charge carrier dynamics in monolayer WS2 on gold (Au) and fused silica (SiO2) using time-domain THz emission spectroscopy. For laser excitation above the band gap of WS2, we independently extract effective transport times for both electrons and holes and find that discontinuous WS2 contacts on rough Au generate larger net transient photocurrents than uniform, strongly coupled interfaces ─ a counterintuitive observation attributed to imbalanced electron and hole transfer from WS2 to Au. Crucially, we demonstrate that ultrafast charge extraction and separation suppress recombination-driven energy release and thereby prevent photo-induced degradation under ambient conditions, eliminating the need for encapsulation. These findings redefine interfacial design as a central control parameter for both performance and stability in 2D optoelectronic devices.