Ultrafast photophysics of metal halide perovskite multiple quantum wells: device implications and reconciling band alignment

Metal halide perovskite quantum wells (QWs) have been used to fabricate efficient optoelectronic devices, and exhibit stability superior to that of their bulk 3D counterparts. The perovskite QWs are tuned in synthesis so that they possess different bandgaps and exciton binding energies owing to variable quantum confinement as a function of QW thickness. Accordingly, the device performance of these materials depends on the efficiency of various interwell carrier dynamical processes, principally exciton and charge transfer. I will discuss the use of transient absorption and ultrafast two-dimensional electronic spectroscopy to probe interwell exciton transfer on timescales of 100s of femtoseconds, and show that interwell charge transfer occurs on timescales of 10s to 100s of picoseconds. These results, in addition to photoelectron spectroscopy experiments, are used to reconcile conflicting observations of type-I and type-II band alignment amongst perovskite QWs.