The Role of Inorganic Ruddlesden-Popper Planar Faults in CsPbBr₃ Perovskite Nanocrystals and Their Performance in LEDs

Ruddlesden-Popper (RP) planar faults composed of organic layers were shown to significantly enhance stability and overall opto-electronic performance of lead-halide perovskite nanocrystals (PNCs). The observed phenomena have been mainly attributed to the moisture-repellant and electronically insulating nature of long carbon chains allowing them to shield perovskite domains from moisture while confining excitons. Similar performance enhancement is seen in PNCs with all-inorganic RP layers – insulating in nature, yet highly soluble in water. Here we attempt to define the role of CsBr RP-faults in CsPbBr₃nanocrystals by performing a comparative analysis of nanocrystals with and without RP layers. The nanocrystals are studied as stand-alone colloids and thin films as well as emissive layers in light-emitting diodes. We find that CsPbBr₃PNCs with RP faults possess both higher exciton binding energies and longer exciton lifetimes. The former is ascribed to a quantum confinement effect in the PNCs induced by electronically insulating CsBr layers. The latter is attributed to a plausible spatial electron−hole separation across the RP faults. A striking difference is seen in the up-conversion photoluminescence response from CsPbBr₃PNCs with and without RPs. For the first time, all-inorganic CsPbBr₃PNCs with RP faults are tested in light-emitting devices and demonstrated to significantly outperform non-RP CsPbBr₃PNCs.