Optical absorption spectra and interlayer excitonic transitions in bulk transition metal dichalcogenides from first principles*

Transition metal dichalcogenides (TMDs) comprise a class of layered materials highly attractive for optoelectronics due to their scalability and thickness-dependent electrical and optical properties. While significant attention has been given to single-layer TMDs, a rather limited number of works have accurately addressed the optoelectronic properties of the few-layer case, which still retains many of the features of the monolayer case. Here, we will present the electronic and optical properties of bulk 2H group VIB TMDs. We performed many-body perturbation theory (MBPT) simulations to compute the quasiparticle bandstructure within G0W0, and subsequently solve Bethe-Salpeter equation for the optical absorption including electron-hole correlations. Our results correlate extremely well with existing experimental results, particularly for the excitonic peaks. We show that, due to the symmetry of the bands, the first exciton present in all these systems is dark, occurring in the vicinity of K point, whereas the brighter excitons occur in H-K high-symmetry direction, with transitions between the VBM and CBM+1, and strong interlayer component. Using that information, we estimate the theoretical photovoltaic performance of these group VIB TMDs by calculating the short-circuit current, open-circuit voltage, and power conversion efficiency, presenting values higher than semiconductors of similar width.