Band Alignment in Core-Shell Nanocrystals by Estimating Wave Function Tunneling Probabilities

Core-shell colloidal semiconducting nanocrystals (NCs) have tremendous optoelectronic applications due to their high quantum yields and chemical stability, but their complex interfaces, across which electron and hole confinement varies, make quantifying confinement and core-shell band offsets challenging for both theory and experiment. We employ a new, reliable, and simple-to-use density functional theory-based approach to estimate wave function tunneling probabilities between core and shell materials from first-principle atomistic simulations. We investigate electron/hole confinement in II-VI core-shell nanocrystals and find that band offsets in Type-I, Type-II, and quasi-Type-II heterostructures qualitatively follow the bulk trend. Quantitatively, we find that the level alignment is sensitive to the lattice match between core and shell, nanocrystal shape, and shell thickness. In general, we observe that the electron and hole wave functions can tunnel substantially across the core-shell interface, which has implications for the effectiveness of passivation of various core-shell heterostructures.