Outside Back Cover: Surface defects have been considerable issues for the perovskite quantum dots light-emitting diodes (PeQLEDs). In the work of doi:10.1002/idm2.12164, Tong et al. report an in-situ surface passivation to PeQDs by introducing the metal cations competitive lattice occupancy assisted with acid-etching, achieving an external quantum efficiency of 8.42% for pure blue PeQLEDs.