  Using first-principles calculations based on density-functional theory, we
investigated the adsorption of pentacene molecules on monolayer two-dimensional
transition metal dichalcogenides (TMD). We considered the four most popular
TMDs, namely, MoS$_2$, MoSe$_2$, WS$_2$ and WSe$_2$, and we examined the
structural and electronic properties of pentacene/TMD systems. We discuss how
monolayer pentacene interacts with the TMDs, and how this interaction affects
the charge transfer and work function of the heterostructure. We also analyse
the type of band alignment formed in the heterostructure and how it is affected
by molecule-molecule and molecule-substrate interactions. Such analysis is
valuable since pentacene/TMD heterostructures are considered to be promising
for application in flexible, thin and lightweight photovoltaics and
photodetectors.
