Interfacial “Anchoring Effect” Enables Efficient Large‐Area Sky‐Blue Perovskite Light‐Emitting Diodes

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 holedominated blue PeLED, we propose to insert a cesium acetate (CsAc) layer between the hole transport layer (HTL) and the holedominant 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 PbBr 2 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.

Section: Resultsmentioning

confidence: 99%

“…Surface modification on the transport layer has been demonstrated to be effective in enhancing the crystallinity of perovskites and improving the carrier transport capability. 42 Therefore, we also conducted structural and optical investigations on the perovskite film without and without the CsAc layer.…”

Section: Resultsmentioning

confidence: 99%

Spatial Control of the Hole Accumulation Zone for Hole-Dominated Perovskite Light-Emitting Diodes by Inserting a CsAc Layer

Zhu

Guan

et al. 2023

“…Electrochemical impedance spectroscopy (EIS) characterizations were conducted to analyze charge transport and recombination behaviors in the our fabricated QLEDs. , Figure b shows the Nyquist plots of QLED devices based on the pristine TFB and the cross-linked TFB:X1 under a forward bias voltage of 3.0 V. The inset of Figure b is the simplified equivalent circuit model, consisting of capacitors and parallel and series resistors. The serial resistance ( R s ) represents the total external resistance including the electrodes, the external wires, and the contact resistance between the electrode and the functional layer.…”

Section: Resultsmentioning

confidence: 99%

Molecular Design of Diazo Compound for Carbene-Mediated Cross-Linking of Hole-Transport Polymer in QLED with Reduced Energy Barrier and Improved Charge Balance

Wei

et al. 2022

Polymeric hole-transport materials (HTMs) have been widely used in quantum-dot light-emitting diodes (QLEDs). However, their solution processability normally causes interlayer erosion and unstable film state, leading to undesired device performance. Besides, the imbalance of hole and electron transport in QLEDs also damages the device interfaces. In this study, we designed a bis-diazo compound, X1, as carbene cross-linker for polymeric HTM. Irradiated by ultraviolet and heating, a poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt(4,4′-(N-(4-butylphenyl))] (TFB)/X1 blend can achieve fast “electronically clean” cross-linking with ∼100% solvent resistance. The cross-linking reduced the stacking behaviors of TFB and thus led to a lower hole-transport mobility, whereas it was a good match of electron mobility. The carbene-mediated TFB cross-linking also downshifted the HOMO level from −5.3 to −5.5 eV, delivering a smaller hole-transport energy barrier. Benefiting from these, the cross-linked QLED showed enhanced device performances over the pristine device, with EQE, power efficiency, and current efficiency being elevated by nearly 20, 15, and 83%, respectively. To the best of our knowledge, this is the first report about a bis-diazo compound based carbene cross-linker built into a polymeric HTM for a QLED with enhanced device performance.

“…17 The rational selection of the interface layer material can regulate the crystallization of the perovskite, 18 align the energy level, 19 reduce interface defects, 20,21 and prevent the interfacial reaction and ion migration from the perovskite film to the transport layer or to the electrode. 22 Tang et al incorporated potassium sulfate (K 2 SO 4 ), 18 amino-functionalized ethanolamine (ETA), 23 and 2-amino-1,3-propanediol (APDO) 24 into the PEDOT:PSS solution. Their experimental results showed that all three molecules reduced the contact angles of the precursor solutions on PEDOT:PSS film to a certain extent and improved the hydrophilicity of the PEDOT:PSS substrate.…”

Section: Introductionmentioning

confidence: 99%

Interface Engineering with Quaternary Ammonium-Based Ionic Liquids toward Efficient Blue Perovskite Light-Emitting Diodes

Yan

Liu

et al. 2022

Perovskite light-emitting diodes (PeLEDs) have become a hot research topic in recent years and can now achieve an external quantum efficiency (EQE) of over 22% for green and red devices. However, the efficiency of blue PeLEDs, which are essential for display applications, lags far behind their green and red counterparts. The interface of the PeLEDs has a critical influence on the carrier transport and exciton recombination dynamics, and interface engineering is considered to be an effective strategy to improve the device performance. Herein, quaternary ammonium-based ionic liquids serve as an interfacial modification layer to significantly improve the device efficiency and stability. The interaction of quaternary ammonium cations with Pb(Br/Cl)6 octahedra promotes nucleation sites, which significantly improves the morphology of perovskite films and reduces the formation of defects in films. In addition, ion migration is also effectively suppressed in the device. As a result, with tributylmethylammonium bromide (TMAB) used as the interface layer, the EQE of the device is successfully increased from 3.5 to 6.7%, and the operational stability with a half-lifetime (T 50) is increased by over 12 times. Our work provides a new class of interface modification materials toward high-performance blue PeLEDs.