The unique photoelectronic properties of the two-dimensional Janus MoSSe/WSSe superlattice: a first-principles study

Designing photocatalysts with suitable band alignment and considerable carrier mobility is extremely important. Here, by means of first-principles calculation, we systematically investigated the structural, photoelectronic, and carrier mobility behavior of the two-dimensional Janus MoSSe/WSSe superlattice. The results show that both armchair-type (A_N-SL) and zigzag-type (Z_N-SL) superlattices are relatively stable with negative E_f values in the range of -2.35 to -1.16 eV. Band gap and band edge position calculations demonstrate that these superlattices are completely suitable for water splitting by visible light. Particularly, the interface contact of the superlattice can be spontaneously changed from type-I to type-II when N > 4, facilitating separation of photogenerated carriers. Furthermore, the hole carrier mobility (μ_h) in A_N-SL can be effectively regulated from 1200 to 2200 cm² V^-1 s^-1, much larger than that of the isolated components. Interestingly, the disparity of hole/electron carrier mobility is remarkably large with an approximately 20-fold difference, showing the potential in prohibiting the recombination of photogenerated carriers. This unique behavior is further illustrated by the relaxation times of carriers, where the lifetime of hole carriers is about 7 times larger than that of electron carriers. These findings suggest that forming a Janus superlattice is a promising approach for regulating the photoelectronic properties of semiconductors, providing a promising way to design high efficiency photocatalysts.