quasi-2D Perovskite Research Articles

High-Performance Perovskite Light-Emitting Diodes Enabled by Passivating Defect and Constructing Dual Energy-Transfer Pathway through Functional Perovskite Nanocrystals.

Quasi-2D perovskites have emerged as a promising luminescent material for perovskite light-emitting diodes (Pe-LEDs). However, efficiency and stability are still obstacles to practical application due to numerous defects and inefficient energy transfer of perovskite films. Herein, functional phenethylammonium bromine-modified CsPbBr3 nanocrystals (PEA-CsPbBr3 NCs) are first introduced as multifunctional additive to simultaneously improve abovementioned problems. PEA-CsPbBr3 NCs not only serve as heteronuclear seeds and trigger growth, thus greatly reducing leakage current, but also deliver Cs+ and Br- to passivate the intrinsic defects inside film. More importantly, the PEA-CsPbBr3 construct a new carrier-transfer pathway from the small-n phase of the quasi-2D perovskite to the PEA-CsPbBr3 , which not only accelerates the energy-transfer process but also promotes radiation recombination of carriers due to stronger quantum confinement effect. Afterward, the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate/poly[9,9-dioctylfluoreneco-N-[4-(3-methylpropyl)]diphenylamine]:black phosphorus quantum dot double hole-transport layer is successfully constructed to enhance its carrier-injection and charge-transport abilities. Consequently, a champion external quantum efficiency of 25.32% and maximal brightness of 128 842cd m-2 are achieved, which is the record efficiency of the quasi-2D Pe-LED with pure green emission at 530nm. Moreover, an impressive 174min lifetime is obtained at T50 , which is about five times longer than the control device.

Stabilized Low-Dimensional Species for Deep-Blue Perovskite Light-Emitting Diodes with EQE Approaching 3.4.

Despite recent encouraging developments, achieving efficient blue perovskite light-emitting diodes (PeLEDs) have been widely considered a critical challenge. The efficiency breakthrough only occurred in the sky-blue region, and the device performance of pure-blue and deep-blue PeLEDs lags far behind those of their sky-blue counterparts. To avoid the negative effects associated with dimensionality reduction and excess chloride typically needed to achieve deep-blue emission, here we demonstrate guanidine (GA+)-induced deep-blue (∼457 nm) perovskite emitters enabling spectrally stable PeLEDs with a record external quantum efficiency (EQE) over 3.41% through a combination of quasi-2D perovskites and halide engineering. Owing to the presence of GA+, even a small inclusion of chloride ions is sufficient for generating deep-blue electroluminescence (EL), in clear contrast to the previously reported deep-blue PeLEDs with significant chloride inclusion that negatively affects spectral stability. Based on the carrier dynamics analysis and theoretical calculation, GA+ is found to stabilize the low-dimensional species during annealing, retarding the cascade energy transfer and facilitating the deep-blue EL. Our findings open a potential third route to achieve deep-blue PeLEDs beyond the conventional methods of dimensionality reduction and excessive chloride incorporation.

Low amplified spontaneous emission threshold from 2-thiophenemethylammonium quasi-2D perovskites via phase engineering.

Quasi-2D Ruddlesden-Popper perovskites attract great attention as an optical gain media in lasing applications due to their excellent optoelectronic properties. Herein, a novel quasi-2D Ruddlesden-Popper perovskite based on 2-thiophenemethylammonium (ThMA) is synthesized by a facile solution-processed method. In addition, an anti-solvent treatment method is proposed to tune the phase distribution, and preferential orientation of quasi-2D (ThMA)2Csn-1PbnBr3n+1 thin films. The large-n-dominated narrow domain distribution improves the energy transfer efficiency from small-n to large-n phases. Also, the highly oriented nanocrystals facilitate the efficient Förster energy transfer, beneficial for the carrier population transfer. Furthermore, a green amplified spontaneous emission with a low threshold of 13.92 µJ/cm2 is obtained and a single-mode vertical-cavity laser with an 0.4 nm linewidth emission is fabricated. These findings provide insights into the design of the domain distribution to realize low-threshold multicolor continuous-wave or electrically driven quasi-2D perovskites laser.

Modification of PEDOT: PSS to enhance device efficiency and stability of the Quasi-2D perovskite light-emitting diodes

Poly(3,4-ethylenedioxy thiophene): poly(styrene sulfonate) (PEDOT: PSS) is a hole transport layer (HTL) that is often employed in a diverse array of optoelectronic devices, such as perovskite solar cells and perovskite light-emitting diodes (PeLEDs). By simply doping lithium fluoride (LiF) into PEDOT: PSS, we demonstrate that the electrical characteristics of the HTL can be modified. Especially in quasi-2D perovskite LEDs, the crystallization process is regulated by LiF modification, leading to reduced phase impurity defects and improved carrier transport in the perovskite emission layer. Therefore, the luminance and efficiency of the quasi-2D PeLEDs are notably enhanced. The optimized PeLED with LiF modification exhibits a peak luminance of 21517 cd m −2 with 317% higher than the standard PeLED; and a high current efficiency of 39.8 cd A −1 with 237% higher than the standard PeLED. Moreover, the device stability is also improved with a nearly doubled half lifetime due to the reduced phase impurities. The work demonstrates a facile yet effective method for altering PEDOT: PSS hole transport layer, emphasizing the critical role of the underneath layer in the crystallization of quasi-2D perovskites. PEDOT: PSS with LiF modification can notably improve the device efficiency and stability of quasi-two-dimensional perovskite light-emitting diodes. • Electronic properties of the hole transport layer can be modified by lithium fluoride doping. • Reduced phase impurity defects and improved carrier transport. • Device stability is also improved with a nearly doubled half lifetime.

Monolithic Integration of Perovskite Photoabsorbers with IGZO Thin‐Film Transistor Backplane for Phototransistor‐Based Image Sensor

AbstractMonolithic integration of perovskite materials and their optoelectronic devices with well‐developed thin‐film transistor (TFT) backplane is leading to new applications in displays and image sensors. Herein, a scalable polyimide assisted patterning approach for monolithic integration of perovskite based high‐sensitive phototransistor array on indium gallium zinc oxide (IGZO) active matrix backplane is introduced. Polyimide vias are first formed by conventional photolithography process, through which uniform perovskite films of arbitrary patterns with feature size less than 20 µm are fabricated by spin‐on‐patterning method. Using this technique, patterns of quasi 2D perovskite photoabsorbing layer are precisely deposited onto the channel area of the photosensing IGZO TFT, forming high‐performance phototransistors with responsivity and detectivity reaching 835.7 A W−1 and 5.4 × 1012 Jones, respectively. An image sensor with 8 × 8 pixels array containing both photosensing perovskite/IGZO transistors and switching IGZO transistors is demonstrated, in which the switching IGZO transistor elements on the backplane are protected by the non‐patterned region of the polyimide encapsulation layer. This whole fabrication process is compatible with TFT manufacturing process and will significantly reduce the cost needed for constructing next generation high‐resolution image sensors.

Exciton Transfer Dynamics and Annihilation in Rubidium–Cesium-Alloyed, Quasi-Two-Dimensional Perovskite

Light-emitting diodes (LEDs) based on perovskite materials are a new group of devices that are currently undergoing rapid development. A significant fraction of these devices is based on quasi-2D perovskites fabricated with large organic cations. In this work, we describe the ultrafast scale dynamics in a quasi-2D PEA2(Rb0.6Cs0.4)2Pb3Br10 perovskite material with an excess of RbBr, which was previously used to fabricate blue-emitting perovskite LEDs. The results obtained using transient absorption spectroscopy are consistent with the assumption that the carrier dynamics in this material are dominated by excitons, most of which decay by exciton–exciton annihilation when high-intensity excitation is used. Furthermore, a slow energy transfer between different quasi-2D domains taking place within 50 ps was observed. The content of the RbBr did not show any strong influence on the observed dynamics. Our results show that the exciton–exciton annihilation proceeds much faster in thin (n = 2) quasi-2D domains than in thick (n ≥ 4) domains. This finding implies that perovskites with high-n, quasi-2D domains are preferable for efficient perovskite lasers and bright perovskite LEDs.

Enhanced efficiency and stability of Dion–Jacobson quasi-two-dimensional perovskite solar cells by additive

Dion–Jacobson (DJ) quasi-two-dimensional (quasi-2D) perovskite solar cells (PSCs) have attracted increasing attention owing to their potential stability compared with the Ruddlesden-Popper (RP) phase. It is known that the low efficiency and poor thermal stability retard the application of quasi-2D PSCs. Here, DJ quasi-2D perovskite films based on propane-1.3-diammonium (PDA) spacer cations were prepared by a hot casting technique. Ionic liquid additive of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) was introduced into the quasi-2D perovskite precursor solution to improve the crystal quality and morphology of the films. The quasi-2D PSCs with BMIMBF4 achieved an optimal power conversion efficiency (PCE) of 14.07%, which is higher than the 12.45% of the control devices. The impressive 1.17 V high open-circuit voltage and 14.07% efficiency are the highest values for the reported PDA-based n–i–p type devices. Moreover, the thermal stability of the solar cells was significantly enhanced by the addition of BMIMBF4. The PCE of the devices with BMIMBF4 maintains 72% of the initial value after annealing at 85 °C for 120 h, while the PCE of control devices drops to 19% of the initial value. These results prove that the introduction of ionic liquid BMIMBF4 is a pragmatic method to elevate the efficiency and thermal stability of quasi-2D PSCs.

Red Perovskite Light-Emitting Diodes with Efficiency Exceeding 25% Realized by Co-Spacer Cations.

Perovskite light-emitting diodes (PeLEDs) have received great attention in recent years due to their narrow emission bandwidth and tunable emission spectrum. Efficient red emission is one of most important parts for lighting and displays. Quasi-2D perovskites can deliver high emission efficiency due to the strong carrier confinement, while the external quantum efficiencies (EQE) of red quasi-2D PeLEDs are inefficient at present, which is due to the complex distribution of different n-value phases in quasi-2D perovskite films. In this work, the phase distribution of the quasi-2D perovskite is finely controlled by mixing two different large organic cations, which effectively reduces the amount of smaller n-index phases, meanwhile the passivation of lead and halide defects in perovskite films is realized. Accordingly, the PeLEDs show 25.8% EQE and 1300cd m-2 maximum brightness at 680nm, which exhibits the highest performance for red PeLEDs up to now.

Stable Yellow Light-Emitting Diodes Based on Quasi-Two-Dimensional Perovskites.

Perovskite light-emitting diodes (PeLEDs) show great potential in display and lighting because of their tunable wavelength, narrow emission bandwidths, and high color purity. Currently, the external quantum efficiency (EQE) of red and green PeLEDs has reached >23%. However, yellow PeLEDs are still rarely reported because of phase separation in mixed-halide perovskites and the coexistence of multiple phases in quasi-two-dimensional (quasi-2D) perovskites L2An-1BnX3n+1 (n = 1, 2, 3, ...), where L is a bulky organoammonium ligand. Here, we fabricate stable yellow PeLEDs by manipulating the phase distribution and incorporating rubidium cations (Rb+) in quasi-2D perovskites. The transient absorption results confirm that alkylammonium ligand butyl ammonium (BA) has a narrower phase distribution than phenylethyl ammonium (PEA) in the quasi-2D perovskites, resulting in a more blue-shifted emission peak. We further incorporate a proper molar ratio of Rb+ in the (BA)2CsPb2I7 perovskite to blue-shift the emission peak to the yellow range. Finally, the yellow PeLEDs exhibit an EQE of 3.5%, and the stable emission peak is located at 595 nm. Our work provides a useful approach for the fabrication of highly efficient and stable yellow PeLEDs.

Enhanced Amplified Spontaneous Emission in Quasi-2D Perovskite by Facilitating Energy Transfer.

Despite the superior optoelectronic properties of quasi-two-dimensional (quasi-2D) Ruddlesden-Popper halide perovskites, the inhomogeneous distribution of mixed phases result in inefficient energy transfer and multiple emission peaks. Herein, the insufficient energy funneling process at the high-energy phase is almost completely suppressed and the excitonic understanding of gain nature is studied in the energy funneling managed quasi-2D perovskite via introducing poly(vinyl pyrrolidone) (PVP) additive. The energy transfer process is facilitated from 0.37 to 0.26 ps after introducing the PVP additive, accelerating the exciton accumulation in the emissive state, and increasing the ratio of the high-dimensional phase for enhancing radiative emission. The gain lifetime is promoted to be as fast as 28 ps to outcompete nonradiative recombination during the build-up of population inversion. Simultaneously, the net gain coefficient is increased by more than twofold that of the pristine perovskite film. Owing to the remarkable gain properties, room-temperature amplified spontaneous emission is realized with a low threshold of 11.3 μJ/cm2, 4 times lower than 43 μJ/cm2 of the pristine film. Our findings suggest that the PVP-treated quasi-2D perovskite shows great promise for high-performance laser devices.

Modulating phase distribution and passivating surface defects of quasi-2D perovskites via potassium tetrafluoroborate for light-emitting diodes

Quasi-two-dimensional (quasi-2D) perovskites show high potential for perovskite LEDs (PeLEDs) due to a bit larger exciton binding energy and favorable energy transfer as a result of the natural quantum well structure. However, various-n phases and a large number of surface defects within the quasi-2D perovskites generally result in unfavorable energy transfer and serious nonradiative recombination during the electroluminescence (EL) of PeLEDs. Herein, potassium tetrafluoroborate (KBF4) is applied to fine modulate the phase distribution and simultaneously reduce the defect density of quasi-2D perovskites. The results reveal that the introduction of BF4- ions into the quasi-2D perovskites substantially suppresses the nucleation of small-n phases and induces the nucleation of intermediate-n phases to realize an effective cascade carrier transfer, which could accelerate the carrier transfer from small-n phases to high-n phases within the quasi-2D perovskites. Meanwhile, BF4- ions could also fill the Br- anion vacancies of the quasi-2D perovskites to diminish the nonradiative recombination. Consequently, the PeLED shows the maximum external quantum efficiency (EQE) of 13.92% with a high luminance of 19882 cd m−2. This work provides a new avenue to manipulate the phase distribution and defect passivation of quasi-2D perovskites for high-performance PeLEDs.

(Invited) Surface/Interface Structures of Perovskite Films Studied By Electron Spectroscopies

Interface of perovskite layer play a crucial role in the charge extraction and recombination process of perovskite solar cell. It is, therefore, of great importance to examine the geometrical and electronic structures of surface/interface of perovskite. Unfortunately, standard experimental techniques such as X-ray diffraction (XRD) and scanning tunneling microscopy (STM) are not suitable to examine practical perovskite films for solar cells. XRD observes the lattice periodicity and is not sensitive to the surface structure. Although STM can precisely observe the surface atoms, it cannot be applied to rough surface or thick films, e.g. solution-processed perovskite surface.We have demonstrated that a combination of electron spectroscopies is powerful and versatile tool to examine both geometrical and electronic structures of perovskite surfaces. Figure 1 shows principles of ultraviolet photoelectron spectroscopy (UPS) and metastable atom electron spectroscopy (MAES). In UPS, the valence electrons are excited by ultraviolet photons (typically with the energy of 21.22 eV) and kinetic energies of photoelectrons are analyzed to measure the valence electronic states as a difference between the photon and electron kinetic energies. The probing depth of UPS is limited by the mean free path of electrons which is usually several layers a few nanometers (several layers) in the energy range of UPS. In MAES, the excitation source is replaced with the metastable helium atom (with the energy of 19.82 eV). Although the process as electron spectroscopy is similar to that of UPS, MAES is extremely surface sensitive because the helium atom can only interact with the outermost atomic orbitals of the sample surface. By comparing the UPS and MAES spectra, we can obtain information about the surface structure as well as the electronic states. In this presentation, we will demonstrate the following two topics:1. Surface termination of CH3NH3PbI3 [1]The properties of the interface of perovskite ABX3 should be strongly affected by the surface termination, i.e. whether the surface is terminated with AX or BX layer. We examined the surface termination of a CH3NH3PbI3 thin film prepared by the standard one-step solution process. The results show that surface of the perovskite film is terminated with the layer consisting of CH3NH3 and I.2. Surface structure of quasi-2D perovskite films, PEA2m(CH3NH3)n-2mPbnI3n [2]A small amount of large organic cations incorporated in perovskite film (quasi-2D) passivates the surface and enhances the stability of the perovskite solar cell against moisture. We examined surface structure of PEA2m(CH3NH3)n-2mPbnI3n, and confirmed that the PEA segregates to the surface and that the phenyl group covers the outermost surface of the quasi-2D perovskite. From the concentration dependence, we also examined the plausible structure of the quasi-2D film.1) A. Mirzehmet, T. Ohtsuka, S. A. Abd. Rahman, T. Yuyama, P. Krüger, H. Yoshida, Adv. Mater. 33, 2004981 (2021).2) A. Mirzehmet, T. Ohtsuka, S. A. Abd. Rahman, T. Aihara, M. A. Kamarudin, S. R. Sahamir, S. Hayase, T. Yuyama, P. Krüger, H. Yoshida, Appl. Phys. Express 14, 031006 (2021).

Narrowing the Phase Distribution of Quasi-2D Perovskites for Stable Deep-Blue Electroluminescence.

Solution‐processed quasi‐2D perovskites contain multiple quantum wells with a broad width distribution. Inhomogeneity results in the charge funneling into the smallest bandgap components, which hinders deep‐blue emission and accelerates Auger recombination. Here, a synthetic strategy applied to a range of quasi‐2D perovskite systems is reported, that significantly narrows the quantum well dispersity. It is shown that the phase distribution in the perovskite film is significantly narrowed with controlled, simultaneous evaporation of solvent and antisolvent. Modulation of film formation kinetics of quasi‐2D perovskite enables stable deep‐blue electroluminescence with a peak emission wavelength of 466 nm and a narrow linewidth of 14 nm. Light emitting diodes using the perovskite film show a maximum luminance of 280 cd m–2 at an external quantum efficiency of 0.1%. This synthetic approach will serve in producing new materials widening the color gamut of next‐generation displays.

Universal Bifacial Stamping Approach Enabling Reverse-Graded Ruddlesden-Popper 2D Perovskite Solar Cells.

Quasi 2D perovskite solar cells (PSCs) are promising light absorbers that overcome the inherent instabilities of 3D perovskites. High-performance and stable 2D PSCs require careful control over the crystallographic orientation and phase distribution. This study introduces a simple and universal bifacial stamping method to obtain highly oriented perovskite crystals with a reverse-graded structure, where the low-n-value 2D perovskite phases are located mainly at the film surfaces. Bifacial stamping of 3D perovskite films atop the 2D films enables incorporation of 2D spacer cations into the 3D film surfaces, forming reverse-graded quasi-2D perovskite films. During stamping, suppressed evaporation of the precursor solvent induces heterogeneous nucleation from the contact interface between the 2D and 3D films, resulting in well-crystallized perovskite films having out-of-plane alignments with respect to the substrate. Thus, a highly oriented and reverse-graded quasi-2D perovskite with an average n value of 18 is obtained with power conversion efficiency exceeding 17% and high open-circuit voltage of 1.11V for iso-butylammonium (iso-BA)-based (iso-BA2 MAn -1 Pbn I3 n +1 ) PSCs. The unencapsulated device retains 92% of its initial efficiency after aging at 40 ± 5% relative humidity for 1200 h. This work provides a new strategy for fabricating highly oriented and phase-controlledquasi-2D PSCs.

Diammonium-Mediated Perovskite Film Formation for High-Luminescence Red Perovskite Light-Emitting Diodes.

3D mixed-halide perovskite-based red emitters combine excellent charge-transport characteristics with simple solution processing and good film formation; however, light-emitting diodes (LEDs) based on these emitters cannot yet outperform their nanocrystal counterparts. Here the use of diammonium halides in regulating the formation of mixed bromide-iodide perovskite films is explored. It is found that the diammonium cations preferentially bond to Pb-Br, rather than Pb-I, octahedra, promoting the formation of quasi-2D phases. It is proposed that the perovskite formation is initially dominated by the crystallization of the thermodynamically more favorable 3D phase, but, as the solution gets depleted from the regular A cations, thin shells of amorphous quasi-2D perovskites form. This leads to crystalline perovskite grains with efficiently passivated surfaces and reduced lattice strain. As a result, the diammonium-treated perovskite LEDs demonstrate a record luminance (10745cd m-2 ) and half-lifetime among 3D perovskite-based red LEDs.

Amine-Terminated Carbon Dots Linking Hole Transport Layer and Vertically Oriented Quasi-2D Perovskites through Hydrogen Bonds Enable Efficient LEDs.

Close attention to the interfaces of solution-processed metal halide perovskite-based light-emitting devices (LEDs) is crucial for their optimal performance. Solution processing of these devices typically leads to the formation of van der Waals interfaces with a weak connection between different functional layers, leaving great room for improvement in charge transport through strengthening of the interlayer interaction. Here, we have realized a hydrogen-bond-assisted interface that makes use of ultrasmall amine-terminated carbon dots to enhance the interaction between the hole transport layer made of PEDOT:PSS and the hybrid lead bromide perovskite emitting layer, which not only promotes the hole injection efficiency but also orients the quasi-2D perovskite crystals penetrating the vertical direction of the device without any, or very few, horizontal grain boundaries, which has a profound effect on the photophysical and transport properties of the emitting layer. As a result, LEDs based on quasi-2D perovskites show up to 24.5% external quantum efficiency, 80 000 cd m-2 brightness, and over 5-fold extended longevity.

Simple method to synthesize larger n 2D perovskite from (C(NH2)3)(CH3NH3)n[PbnI3n+1] of n = 1 using isopropanol

Two-dimensional (2D) perovskite of (C(NH 2 ) 3 )(CH 3 NH 3 ) n [Pb n I 3n+1 ] (shorten as (GA)MA n [Pb n I 3n+1 ]) is with alternating cations (GA + and MA + ) in the interlayer space (ACI). n = 1 of (GA)MAPbI 4 film can transform from red to black in appearance after soaking in isopropanol (IPA) for 5 s, resulting in the peaks of PL from 570 nm to 770 nm. Using X-ray diffraction and Fourier-transform infrared spectroscopy, we find that the IPA can dissolve GA + cation from the film effectively, thus n = 1 layered structure is destroyed, leaving larger n phases of (GA)MA n [Pb n I 3n+1 ] in film. By controlling the reaction time with IPA solvent, the n = 1 film can rearrange into new material of mixture with various n values, which present tunable absorption and photoluminescence spectra. Our work may not only explore the novel phenomena of ACI 2D perovskite, but also provide a simple method to synthesize quasi 2D perovskite with adjustable n values. • Isopropanol (IPA) can solve GA + effectively from (GA)MAPbI 4 film. • Large n phases of (GA)MA n [Pb n I 3n+1 ]) was left after IPA treatment. • Modifying the reaction time of (GA)MAPbI 4 film can achieve tunable n materials. • The novel phenomena of ACI 2D perovskite.

Quantum Confinement and Dielectric Deconfinement in Quasi-Two-Dimensional Perovskites: Their Roles in Light-Emitting Diodes

In quasi-two-dimensional (quasi-2D) perovskites, inorganic quantum wells are sandwiched between organic spacers (barriers) from the energy-level perspective. In addition to quantum confinement, dielectric confinement occurs in the layered perovskites due to a large difference in the dielectric constants of the inorganic framework and the organic spacer layer. While quantum confinement increases the exciton binding energy, deconfinement in the dielectric constant results in a decrease in exciton binding energy and also an increase in carrier mobility. In this work, we investigate the effects of quantum confinement and dielectric deconfinement on the dynamic response of light-emitting diodes (LEDs) based on several series of quasi-2D perovskites and operated under an alternating voltage. With pulsed electroluminescence emission appearing in both bias sections of sinusoidal ac voltages, we show how the quantum confinement and dielectric deconfinement affect and increase the frequency range of ac LED operation, that is, the \ensuremath{-}3 dB cutoff frequency. This \ensuremath{-}3-dB frequency could be seen to increase due to a relaxation of quantum and dielectric confinements, leading to an enhancement of the effective carrier mobility in the active emitting material of the devices.

Rearranging the Phase Distribution of Quasi-2D Perovskite for Efficient and Narrow Emission Perovskite Light-Emitting Diodes.

Quasi-2D perovskite light-emitting diodes (PeLEDs) have attracted significant attention for their promising light-emitting applications. However, quasi-2D perovskite films typically consist of a broad phase distribution and small grains with a large surface area to volume ratio, leading to inferior color purities and higher defect densities. Herein, a bifunctional additive ((l)-tryptophan bromide, l-TrpBr) was introduced into a quasi-2D perovskite film. The C═O moiety of l-TprBr formed hydrogen bonds with S-MBA+, retarding the coordination between S-MBABr and [PbBr6]4- and suppressing the formation of small-n phases. The C═O moiety also coordinated with unsaturated Pb2+ sites to passivate the defects. Finally, the PeLEDs with l-TrpBr exhibited a significantly improved EQE of 14.32% compared to the control devices (7.88%) and the narrowest fwhm (17 nm) for green quasi-2D PeLEDs reported to date. Our work provides a practical approach to controlling the phase distribution and passivating the defects in quasi-2D perovskite films, toward high-efficiency and color-pure quasi-2D PeLEDs.

Enhanced spectral stability of blue perovskite light-emitting diodes via multidentate amine-based ligand

Compared with highly efficient green, red, and near-infrared perovskite light-emitting diodes (PeLEDs), the performance of blue PeLEDs is still unsatisfactory due to the serious spectral instability issue at high working voltages. In this work, a multidentate amine-based ligand with four amino groups is utilized to achieve spectral stable blue quasi-2D PeLEDs. As a result, the optimized quasi-2D perovskite films exhibit stable photoluminescence spectra under continuous UV illumination and heating. Finally, the blue quasi-2D PeLEDs emitting at 478 nm with the peak external quantum efficiency up to 4.8% are achieved. Meanwhile, there is no obvious peak shift of the electroluminescence spectral under high external working voltages, exhibiting excellent spectral stability. The findings in this work confirm the validity of this strategy, providing a strategy to achieve steady blue PeLEDs.