Overcoming Degradation Pathways to Achieve Stable Blue Perovskite Light-Emitting Diodes

Mixed halide (Br/Cl) perovskite nanocrystals(NCs) that represent an advanced blue emitter commonlysuffer from spectral instability and poor lifespan; notably, thelack of understanding of the failure mechanisms of thesedevices has restricted the future progress. Here, we determinethat the degradation of CsPbBrxCl3-xNCs containing bluelight-emitting diodes (LEDs) is due to the combination of twoeffects. Cl-drift among adjoining NCs under an electricfield isfound to induce a Cl-deficient material region in multiple NClayers, which dominates the unstable electroluminescence andcauses fast degradation in the corresponding devices. Incomparison, the monolayer NC devices that feature restricted anion drift pathways exhibit better operational stability;however, excess hole injection is demonstrated to induce irreversible chlorine loss in NCs. Such a process that largely arisesfrom electrochemical oxidation of Cl-initiates a mild device failure in operation of tens of minutes. Through revealing thesemechanisms, we modulate the devices'construction and operational conditions to achieve a longer lifespan.