Interface Engineering of CsPbBr₃ Nanocrystal Light‐Emitting Diodes via Atomic Layer Deposition

Abstract

Perovskite nanocrystal (PNC) suffers from solution corrosion and water/oxygen oxidation when used in light‐emitting diodes (LEDs). Atomic layer deposition (ALD) is applied to introduce Al2O3 infilling and interface engineering for the CsPbBr3 nanocrystal emission layers, and the inorganic electron transport layer‐based CsPbBr3–ZnMgO LED device is fabricated. The introduction of Al2O3 ALD layers significantly improves the tolerance of CsPbBr3 PNC thin films to polar solvents ethanol of ZnMgO during spin coating. The operation lifetime of ALD‐treated CsPbBr3 PNC–ZnMgO LED is prolonged to about two orders of magnitude greater than that of the CsPbBr3 PNC‐TPBi LED device with a largely improved external quantum efficiency (EQE) value. Moreover, the infilling of Al2O3 into the CsPbBr3 layer boosts the carrier mobility for more than 40 times inside the light‐emission layer. However, the interfacial carrier transport between different functional layers is hindered by the insulated Al2O3 layer, which provides an effective barrier for excess electron transport. Such a favorable band alignment facilitates the carrier balance of the device and contributes to the improved electroluminescent performance of the device with ALD Al2O3 interface engineering, which is further supported by theoretical device modeling. Herein, a facile method is provided to fabricate PNC‐LED devices with both high efficiency and long‐term lifetime.

High-Resolution Colloidal Quantum Dot Film Photolithography via Atomic Layer Deposition of ZnO

“…As a result, QD films have a strong resistance to external solvents, and PR can be directly coated on top of the QD. Similar strategies have been attempted in perovskite materials to achieve solvent orthogonality during device fabrication, − but patterning of nanocrystals has been developed for the first time in the present work. In addition to depositing layers of ZnO by a few cycles of ALD, exposing the DEZ for a few seconds is sufficient to provide solvent resistance of the QD film.…”

Atomic layer deposition for quantum dots based devices

“…On the other hand, some works implied that the photoluminescence of QDs after ALD became inferior to those pristine ones 104 . The contradictory conclusion may attribute to the loss of surface ligands 88 or the replacement of QDs cations by metal precursor 69 .…”

Gentle Materials Need Gentle Fabrication: Encapsulation of Perovskites by Gas-Phase Alumina Deposition

“…The introduction of Al 2 O 3 /ZnO ALD layers significantly improves the tolerance of CsPbBr 3 PNC thin films to polar solvents (ethanol) during deposition of electron transport layer and increases the operation lifetime. 48,49 However, in spite of providing conformal overcoating, protection against environmental factors, and improving carrier transport properties, the metal oxide deposition process greatly quenches the photoluminescence of perovskite NCs, 45 with partial decomposition into PbI 2 observed in some cases of MAPbI 3 . 43 Lowering the metal oxide deposition temperature and changing the metal/oxygen precursors have been explored to circumvent this detrimental effect.…”

“…Among a number of surface stabilization strategies, − atomic layer deposition (ALD) of metal oxides has received continuous attention. It has been demonstrated that alumina encapsulation improves long-term stability and retains the integrity of perovskites during device fabrication. , The earliest applications included use of ALD Al 2 O 3 as an overlayer on CH 3 NH 3 PbI 3 sensitized solar cells which could act as a barrier to protect the easily dissolvable perovskite sensitizer. , These were followed by more elaborate approaches where metal oxides were applied throughout perovskite solar cell (PSC) structures as well as for outside encapsulation. − Lately, ALD has been employed to encapsulate fully inorganic perovskites and solution-processed nanocrystals (PNCs) that are developed for LED and laser applications. − However, in spite of being effective for external surface protection and improving carrier transport properties, the metal oxide ALD procedure often diminishes optical properties of the perovskite materials, especially solution-processed PNCs, to a significant extent. More specifically, degradation is attributed to the detrimental reaction of Al precursor with the surface atoms of the material, impeding use of ALD-based encapsulation for applications that require high photoluminescence (PL) quantum yield of the active material. ,,− We highlight how a recently established and developed gas-phase ALD technique enables precise control of the surface reactions and leads to the investigation of the precise atomic interactions taking place on the perovskites’ surfaces during aluminum oxide deposition.…”

“…It relies on the sequential pulsing of individual precursors which react with the material surface in a self-terminating way, thus allowing strict control of the amount (a monolayer) deposited. ,− Over the past decade, ultrathin layers of ALD Al 2 O 3 , ZnO, SnO 2 , and TiO 2 have been used in various PSC architectures to passivate the metal oxide electrode (to suppress interfacial recombination), − between perovskite and a charge transport layer (to decrease interfacial reaction), ,− as cathode buffer layer to protect the perovskite during deposition of the top electrode and reduce interfacial charge recombination, , to produce a pinhole-free electron transport layer for reduced interfacial recombination loss, − or as an overall encapsulation layer for PSCs to protect them from moisture/environment-based degradation. , More recently, AlO x encapsulation by ALD has been reported to improve stability toward exposure to air, irradiation, heat, and water for fully inorganic CsPbBr 3 nanocrystals. − AlO x has been used for infilling and interface engineering of CsPbBr 3 nanocrystal emission layers in LEDs as well. The introduction of Al 2 O 3 /ZnO ALD layers significantly improves the tolerance of CsPbBr 3 PNC thin films to polar solvents (ethanol) during deposition of electron transport layer and increases the operation lifetime. , …”