Strategies for Improving Performance of Blue Perovskite Light-Emitting Diodes

Abstract

Perovskites, as new promising light emission materials, have drawn tremendous attention for applications in lighting and display for their high color purities, high photoluminescence quantum yields (PLQYs), tunable bandgaps, low cost and solution-processibility. External quantum efficiencies (EQEs) of perovskite light-emitting diodes (PeLEDs) have been improved significantly with the highest values exceeding 20% in near-infrared (NIR), red and green regions. However, the EQE of blue PeLEDs is still lagging with the highest EQE of only 16%. Therefore, exploring strategies for improving the performance of blue PeLEDs is of great significance to meet the demand of their applications in full color display and lighting.

First, a highly efficient sky-blue PeLED operating with an EQE of 13.8% based on a quasi-two-dimensional (quasi-2D) structure is achieved. The outstanding efficiency arises from simultaneous suppress on of both triplet and trap-assisted non-radiative energy losses via using a ligand with a high triplet energy and dual-functional passivation groups.

Second, more than one order of magnitude enhancement of EQE and electroluminescence (EL) intensity in blue CsPb(Br/Cl)₃ PeLEDs with an organic cation of 2,2-(ethylenedioxy)bis(ethylammonium) (EDBE) is demonstrated. Upon controlled humidity treatment, crystallinity of the three-dimensional (3D) perovskite phase in EDBE-based perovskite is improved, contributing to an enhancement of PLQY.

Third, inserting a cesium acetate (CsAc) layer between hole transport layer (HTL) and the hole-dominant perovskite layer is adopted to improve EQEs of blue PeLEDs. It was found that 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 suppress exciton quenching. Moreover, the CsAc layer can also improves photophysical properties of the perovskite films by providing an additional Cs source to interact with defect sites of unreacted PbBr₂ in the perovskite film and enhance the crystallinity of perovskite with enlarged crystal grain size. As a result, the EQE of the sky-blue PeLEDs show considerable improvement from 5.3 to 9.2% upon inserting the CsAc layer.

Date of Award	2 Aug 2023
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Chun Sing LEE (Supervisor)