High-performance Perovskite-Nanocrystal Based Red Light Emitting Diodes with Long Operational Lifetime of 317 hours

While there are advances in the external quantum efficiency (EQE) and film photoluminescence quantum yields (PLQY) of perovskite light emitting diodes (PeLEDs), one of the key challenges of red color PeLEDs based on perovskite-nanocrystals (NCs) is the operational stability because of the easy transformation from cubic to orthorhombic structure and the weak bond energy between inorganic surfaces and long-chain capping ligands. In this work, we demonstrate highly efficient and stable PeLEDs with a peak wavelength of 689 nm by adopting thermodynamically stable tetragonal phase CsPbI₃ (b-CsPbI₃) NCs as the emitting layer [1]. The stable b-CsPbI₃was successfully synthesized via incorporating the poly(maleic anhydride-<i>alt</i>-1-octadecene) (PMA) into the precursor. The PMA can interact with PbI₂ in the precursors to regulate the crystallization kinetics of b-CsPbI₃NCs and finally adsorb on the surface of b-CsPbI₃ NCs through strong Pb-O bond to significantly stabilize the b-CsPbI₃ NCs without any crystalline deformation on the NCs crystal structure. Additionally, these chemically crosslinked PMA also significantly reduces deep defects of Pb_Cs via increasing the formation energy and passivating the Pb_Cs deep defects. Moreover, the PMA-incorporated β-CsPbI₃ NCs exhibit increasing exciton binding energy and reducing longitudinal-optical (LO) phonon energy. Benefiting from the improved crystal phase quality with PMA incorporation, the PLQY of b-CsPbI₃ NCs yields an increase from 34% to 89%. The corresponding PeLEDs achieve a high EQE of 17.8% and exhibited superior operational stability with operation time for a device decay to 50% of the initial EL intensity (T₅₀) of 317 h.<br/>[1] H. Li, H. Lin, D. Ouyang, C. Yao, C. Li, J. Sun, Y. Song, Y. Wang, Y. Yan, Y. Wang, Q. Dong, W. C. H. Choy, "Efficient and Stable Red Perovskite Light Emitting Diodes with Operational Stability &gt; 300 h", Adv. Mater., 2008820, 2021.