Perovskites show efficient electroluminescence and are expected to have wide applications in light-emitting diodes (LEDs). However, owing to the unbalanced electron-hole transport properties of some highly luminescent perovskites, a fundamental challenge is that the exciton recombination zone of perovskite LEDs (PeLEDs) typically overlaps with an accumulation of the major carrier. It is known to reduce the performances of PeLEDs, leading to a reduction of efficiency and operation stability due to Auger recombination. To address this issue in a hole-dominated blue PeLED, we propose to insert a cesium acetate (CsAc) layer between the hole transport layer (HTL) and the hole-dominant perovskite layer. Electronic properties indicate that the hole accumulation zone of the device with the CsAc layer shifts away from the perovskite/ETL interface, i.e., the recombination zone, to the HTL/CsAc interface. Separation of the hole accumulation region and the exciton recombination zones substantially suppresses exciton quenching. Moreover, the CsAc layer can also improve the photophysical properties of the perovskite film by providing an extra Cs source to interact with the defect site of unreacted PbBr2 in the perovskite film and enhance the crystallinity of the perovskite with an enlarged crystal grain size. As a result, the external quantum efficiency (EQE) of the sky-blue PeLEDs shows considerable improvement from 5.3 to 9.2% upon inserting the CsAc layer.
Keywords: charge accumulation; charge balance; hole-blocking; light-emitting diodes; perovskite.