Compositionally Graded\nMoS<sub>2<i>x</i></sub>Te<sub>2(1–<i>x</i>)</sub>/MoS<sub>2</sub> van der Waals Heterostructures for Ultrathin\nPhotovoltaic Applications

van der Waals heterojunctions utilizing two-dimensional\n(2D) transition-metal\ndichalcogenide (TMD) materials have emerged as focal points in the\nfield of optoelectronic devices, encompassing applications in light-emitting\ndevices, photodetectors, solar cells, and beyond. In this study, we\ntransferred few-atomic-layer films of compositionally graded ternary\nMoS<sub>2<i>x</i></sub>Te<sub>2(1–<i>x</i>)</sub> alloys onto metal–organic chemical vapor deposition-grown\nmolybdenum disulfide (MoS<sub>2</sub>) as p- and n-type structures,\nleading to the creation of a van der Waals vertical heterostructure.\nThe characteristics of the fabricated MoS<sub>2<i>x</i></sub>Te<sub>2(1–<i>x</i>)</sub>/MoS<sub>2</sub> vertical-stacked\nheterojunction were investigated considering the influence of tellurium\n(Te) incorporation. The systematic variation of parameter <i>x</i> (i.e., 0.8, 0.6, 0.5, 0.3, and 0) allowed for an exploration\nof the impact of Te incorporation on the photovoltaic performance\nof these heterojunctions. As a result, the power conversion efficiency\nwas enhanced by approximately 6 orders of magnitude with increasing\nTe concentration; notably, photoresponsivities as high as ∼6.4\nA/W were achieved. These findings emphasize the potential for enhancing\nultrathin solar energy conversion in heterojunctions based on 2D TMDs.