Blue Perovskite Light-emitting Diodes Research Articles

Two-Dimensional Dion–Jacobson Structure Perovskites for Efficient Sky-Blue Light-Emitting Diodes

Two-dimensional Ruddlesden–Popper (RP) and Dion–Jacobson (DJ) phase perovskites are promising alternatives to fabricate blue perovskite light-emitting diodes (PeLEDs) due to their strong quantum/di...

Stable blue perovskite light-emitting diodes achieved by optimization of crystal dimension through zinc bromide addition

Low-dimensional perovskites have been widely studied as a promising candidate for realizing stable light-emitting diodes (LEDs). However, blue-light-emitting devices generally possess low stability associated with gradually red-shifted emission. To overcome this issue, the effect of zinc bromide (ZnBr2) addition on the regulation of the crystal structures of phenethylammonium and bromine-chlorine mixed inorganic perovskites (PEA-CsPbBrxCl3-x) is investigated. With the ZnBr2 addition, low-dimensional perovskite structures undergo morphological changes, such as thickening of their crystal structures and higher degree of crystal arrangement. Stoichiometric selective characterization reveals that perovskite bonding forces changed from Van der Waals with PEA to ionic with ZnBr2. Meanwhile, ZnBr2 can effectively address the ion defect filling and dimensional structure property switching. Consequently, the optimized ZnBr2-assisted PEA-CsPbBrxCl3-x LED is shown to deliver a high luminance of 1245 cd/m2 along with a high external quantum efficiency of 1.30%. Furthermore, this blue LED exhibits excellent spectral stability, for which only 3-nm red-shift on external excitation (0.1 to 5.0 mA) is observed. Our result clearly shows that ZnBr2 addition effectively improves the stability of blue light-emitting perovskites.

Mixed halide perovskites for spectrally stable and high-efficiency blue light-emitting diodes

Bright and efficient blue emission is key to further development of metal halide perovskite light-emitting diodes. Although modifying bromide/chloride composition is straightforward to achieve blue emission, practical implementation of this strategy has been challenging due to poor colour stability and severe photoluminescence quenching. Both detrimental effects become increasingly prominent in perovskites with the high chloride content needed to produce blue emission. Here, we solve these critical challenges in mixed halide perovskites and demonstrate spectrally stable blue perovskite light-emitting diodes over a wide range of emission wavelengths from 490 to 451 nanometres. The emission colour is directly tuned by modifying the halide composition. Particularly, our blue and deep-blue light-emitting diodes based on three-dimensional perovskites show high EQE values of 11.0% and 5.5% with emission peaks at 477 and 467 nm, respectively. These achievements are enabled by a vapour-assisted crystallization technique, which largely mitigates local compositional heterogeneity and ion migration.

Review of blue perovskite light emitting diodes with optimization strategies for perovskite film and device structure

Perovskite light emitting diodes (PeLEDs) have attracted considerable research attention because of their external quantum efficiency (EQE) of >20% and have potential scope for further improvement. However, compared to red and green PeLEDs, blue PeLEDs have not been extensively investigated, which limits their commercial applications in the fields of luminance and full-color displays. In this review, blue-PeLED-related research is categorized by the composition of perovskite. The main challenges and corresponding optimization strategies for perovskite films are summarized. Next, the novel strategies for the design of device structures of blue PeLEDs are reviewed from the perspective of transport layers and interfacial layers. Accordingly, future directions for blue PeLEDs are discussed. This review can be a guideline for optimizing perovskite film and device structure of blue PeLEDs, thereby enhancing their development and application scope.

Unveiling the critical role of ammonium bromide in blue emissive perovskite films.

Implementation of ammonium halides to trigger low-dimensional perovskite formation has been intensively investigated to achieve blue perovskite light-emitting diodes (PeLEDs). However, the general roles of the incorporated ammonium cations on the quality of the perovskite films, as well as device performance, are still unclear. It is indispensable to build a guideline to rationalize ammonium halides for decent blue emissive films. Here, by thoroughly investigating a series of ammonium cations containing the different number of ammonium groups and ionic radius, we reveal that the mechanism beyond the tunable emission wavelength, crystallization kinetics, and spectral stability of the obtained blue perovskite films is highly relevant to the molecular structure of the ammonium cations. In parallel with reducing the dimensionality to form normal Ruddlesden-Popper phases, the incorporated ammonium cations also likely modulate the Pb-Br orbit coupling through A-site engineering and generate either Dion-Jacobson or "hollow" perovskites, providing alternative routes to achieve efficient and stable blue emissive films. Our work paves a way to rationalize ammonium halides to develop prevailing active layers for further improving the performance of blue PeLEDs.

High-efficiency sky blue perovskite light-emitting diodes with ammonium thiocyanate additive

Metal halide perovskite light-emitting diodes have attracted much attention due to their excellent characteristics such as low-cost solution-processing, high luminous efficiency and excellent color purity. However, low luminous efficiency and spectrum stability of blue perovskite light-emitting device restrict the further development of perovskite materials in the field of displays and lighting. Here in this work, we study the effects of ammonium thiocyanate (NH<sub>4</sub>SCN) addition on the morphology, crystal structure, photo-physics, charge transport and electroluminescence properties of quasi-two-dimensional mixed-halide perovskite films by measuring scanning electron microscope (SEM), X-ray diffraction (XRD), UV-Vis spectrum, steady-state photoluminescence (PL), and transient PL and analyzing the current density–voltage characteristics of hole-dominated device and current density-voltage-luminance plots of light-emitting device. The results indicate that ammonium thiocyanate (NH<sub>4</sub>SCN) can effectively passivate the defects, improve the crystallinity, and modulate the phase distribution of quasi-two-dimensional mixed-halide perovskite film, thereby increasing charge transport and luminescent efficiency. Notably, PL intensity of the 20%-NH<sub>4</sub>SCN sample is 1.7 times higher than that of the control sample, which is attributed to the defect passivation effect of NH<sub>4</sub>SCN probably due to the Lewis acid-base interaction with Pb<sup>2+</sup>. Meanwhile, the hole mobility of the 20%-NH<sub>4</sub>SCN sample is measured to be 1.31 × 10<sup>–5</sup> cm<sup>2</sup>/(V·s), which is much higher than that of the control sample (3.58 × 10<sup>–6</sup> cm<sup>2</sup>/(V·s)). As a result, sky-blue quasi-two-dimensional mixed-halide perovskite light-emitting diode with 20%-NH<sub>4</sub>SCN possesses an EL maximum at 486 nm and a maximum external quantum efficiency (EQE) of 5.83% and a luminance of 1258 cd/m<sup>2</sup>, which are 6.7 and 3.6 times higher than those of the control device without NH<sub>4</sub>SCN, respectively. At the same time, the EL spectra of the 20%-NH<sub>4</sub>SCN device are barely changed under different operating voltages, whereas the EL spectra of the control device show a 7–10 nm red-shift under the same condition, indicating that the NH<sub>4</sub>SCN addition inhibits halide phase separation and improves the EL spectrum stability. In addition, the T<sub>50</sub> operational life-time of the 20%-NH<sub>4</sub>SCN device is measured to be about 110 s, which is superior to that of the control device (39 s) due to improved film quality of NH<sub>4</sub>SCN-modified sample. This research provides a simple and effective method to improve the performances of quasi-two-dimensional mixed-halide perovskite blue-emitting diodes.

Highly stable blue perovskite light-emitting diodes induced by trifluoroacetate

Highly stable blue perovskite light-emitting diodes induced by trifluoroacetate

Chloride-incorporated quasi-2D perovskite filmsviadynamic processing for spectrum-stable blue light-emitting diodes

The spectral stability remains a challenge for blue perovskite light-emitting diodes (PeLEDs) based on mixed-Cl/Br or quasi-2D perovskites. In this work, we control the redshift of the emitting luminescence (EL) peak for devices less than 2 nm.

Perovskite LEDs Performance Enhancement with Nanostructures for Better Light out-Coupling and Stability

In the past a few years, perovskite light-emitting diodes (LEDs) have experienced extremely amazing development. Thanks to the decent optoelectronic properties, perovskite material has made itself a competitive candidate for next-generation displays and lighting. With the great efforts of researchers in this field, the external quantum efficiencies (EQEs) have already surpassed the 20% milestone for both red and green colored perovskite LEDs. Lately, the blue perovskite LEDs have been reported to achieve an EQE higher than 12%.With the fantastic material quality, perovskite material can achieve a super high photoluminescent quantum efficiency (PLQY); therefore, the internal quantum efficiency (QE) for perovskite LEDs can also reach the level of higher than 90%. As a result, the key solution to the further enhancement of the perovskite LEDs performance relies on the light outcoupling for perovskite LEDs.During the past five years, we have devoted ourselves to the development of nanophotonic strategies for the performance enhancement of the perovskite LEDs. The strategies are comprised of two main categories. The first category is using a nanophotonic substrate for perovskite LEDs devices. The structure we designed was a combination of a nanodome coupler with the photonic crystal optical antennas. When the geometry of the structure was delicately optimized, the light supposed to be trapped inside the active layer can be first coupled into the photonic crystals and form guided modes. After that, the photonic crystals, working as optical antennas, can convert the guided modes to the leaky modes and finally the leaky modes can emit to the air. With this strategy, we successfully improved the EQE of the perovskite LEDs from about 8% to 17.5%, which was the record for the MAPbBr3 based perovskite LEDs at that time.The second category of the nanophotonic strategies is making nanostructured active materials instead of using the nanostructured out-coupling substrates. With the exploration of varieties of nanostructures, we finally determined to use the nanowire arrays for the perovskite LEDs study. Intriguingly, we came up with a solution method with the nanoporous template for perovskite nanowires growth. By studying the growth with different template geometries, we found out that the nanowire growth had a strong relationship with the capillary effect. Then we carefully designed the template thickness and the nanowire lengths, and we made the three-dimensional nanowire arrays-based perovskite LEDs. Compared to the planar counterparts, the nanowire-based perovskite LEDs showed an enhanced EQE (from 11% to 16%), which is due to the improved light coupling inside the nanowires (from about 20% to about 45%). More importantly, the operational stability of the nanowire-based perovskite LEDs was also enhanced (T50 increased from 9 min to 35 min). And the long-term stability of the nanowire-based perovskite LEDs was also increased with an enhancement factor of 3 times. It’s also worth noting that, the mechanical robustness of the nanowire-based perovskite LEDs was also enhanced a lot due to the protection by the porous template, and much fewer cracks were created inside nanowires during bendings when compared to the planar counterparts.With the above mentioned two nanophotonic strategies for perovskite LEDs performance (both light-coupling efficiency and stability) enhancement, we demonstrated the advantages of applying nanostructures in perovskite LEDs. By further developing the perovskite material qualities and meanwhile improving the deposition techniques that are more compatible with nanostructures, we believe the EQEs of perovskite LEDs can be further improved to a new milestone soon. Last but not least, the nanophotonic strategies we developed here are not just limited to LEDs; they can be also applied for other device applications such as solar cells, photodetectors, and lasers.

High-Performance Blue Perovskite Light-Emitting Diodes Enabled by Efficient Energy Transfer between Coupled Quasi-2D Perovskite Layers.

While there has been extensive investigation into modulating quasi-2D perovskite compositions in light-emitting diodes (LEDs) for promoting their electroluminescence, very few reports have studied approaches involving enhancement of the energy transfer between quasi-2D perovskite layers of the film, which plays very important role for achieving high-performance perovskite LEDs (PeLEDs). In this work, a bifunctional ligand of 4-(2-aminoethyl)benzoic acid (ABA) cation is strategically introduced into the perovskite to diminish the weak van der Waals gap between individual perovskite layers for promoting coupled quasi-2D perovskite layers. In particular, the strengthened interaction between coupled quasi-2D perovskite layers favors an efficient energy transfer in the perovskite films. The introduced ABA can also simultaneously passivate the perovskite defects by reducing metallic Pb for less nonradiative recombination loss. Benefiting from the advanced properties of ABA incorporated perovskites, highly efficient blue PeLEDs with external quantum efficiency of 10.11% and a very long operational stability of 81.3min, among the best performing blue quasi-2D PeLEDs, are achieved. Consequently, this work contributes an effective approach for high-performance and stable blue PeLEDs toward practical applications.

Strontium Ion B‐Site Substitution for Spectral‐Stable Blue Emitting Perovskite Light‐Emitting Diodes

AbstractHalide perovskites are promising emitters for light‐emitting diodes (LEDs) due to their outstanding optoelectronic properties, i.e., tunable bandgap, high photoluminescence quantum efficiency, and excellent color purity. However, in contrast to their green and red cousins, the present blue perovskite LEDs are still suffering from poor operational lifetime and electroluminescence shift during bias operation, hindering their practical applications in full‐color information displays. Developing rational strategies to achieve efficient and stable blue perovskite LEDs is one of the urgent tasks in this community. Herein, through substituting the Pb site with strontium ions, blue perovskite films with stable emission under relatively harsh working conditions, i.e., high electrical bias, constant thermal heating, and UV illumination, are obtained, which accordingly guarantees spectrally stable blue perovskite LEDs with external quantum efficiency of 4.1%. Moreover, different alkaline‐earth metal ions are also investigated to further explore the effects of B‐site ion substitution on the performance of perovskite LEDs. This work demonstrates an alternative path for the development of spectral‐stable blue perovskite LEDs.

Rearranging Low-Dimensional Phase Distribution of Quasi-2D Perovskites for Efficient Sky-Blue Perovskite Light-Emitting Diodes.

Metal halide perovskites have received much attention for their application in light-emitting diodes (LEDs) in the past several years. Rapid progress has been made in efficient green, red, and near-infrared perovskite LEDs. However, the development of blue perovskite LEDs is still lagging far behind. Here, we report efficient sky-blue perovskite LEDs by rearranging low-dimensional phase distribution in quasi-2D perovskites. We incorporated sodium ions into the mixed-Cl/Br quasi-2D perovskites with phenylethylammonium as the organic spacer and cesium lead halide as the inorganic framework. The inclusion of the sodium ion was found to significantly reduce the formation of the n = 1 phase, which was dominated by nonradiative transition, and increase the formation of other small-n phases for efficient exciton energy transfer. By managing the phase distribution, a maximum external quantum efficiency (EQE) of 11.7% was achieved in the sky-blue perovskite LED, with a stable emission peak at 488 nm. Further optimizing the phase distribution and film morphology with Pb content, we demonstrated the sky-blue devices with the average EQE approaching 10%. This strategy of engineering phase distribution of quasi-2D perovskites with a sodium ion could provide a useful way for the fabrication of high-performance blue perovskite LEDs.

Simultaneous Low-Order Phase Suppression and Defect Passivation for Efficient and Stable Blue Light-Emitting Diodes

Quasi-two-dimensional (quasi-2D) perovskite is rising as a promising luminescent material for blue perovskite light-emitting diodes (PeLEDs). However, typical quasi-2D perovskites show a wide distribution of low-order phases and low efficiency owing to the inefficient energy transfer. Meanwhile, the defects and traps generated during the perovskite crystallization increase nonradiative recombination, further aggravating the external quantum efficiency (EQE). Herein, we demonstrate a unique quasi-2D perovskite with low-order phase suppression and defect passivation for efficient energy transfer and light emission by incorporating a 2D perovskite and an excess ammonium salt into the quasi-2D perovskite solution. By optimizing the new class of quasi-2D perovskite, we achieve blue PeLEDs with the brightness of 1765 cd m–2, EQE of 7.51%, low turn-on voltage of 3.07 V, and long operation lifetime of 3961 s under constant driving current without any shift of the electroluminescence spectra. The work contributes to promoting efficient and stable blue PeLEDs.

Giant efficiency and color purity enhancement in multicolor inorganic perovskite light-emitting diodes via heating-assisted vacuum deposition

Inorganic perovskites (CsPbX3 (X = I, Br, Cl)) have broad prospection in the field of high-definition displaying due to its excellent optoelectronic characteristics. The vacuum deposition process possesses advantages and competitiveness in the industrialized production. However, the performance of light emitting diodes (LEDs) based on vacuum-deposited is incredibly low. Herein, we proposed a heating-assisted vacuum deposition (HAVD) method to construct inorganic perovskite LEDs (PeLEDs) with enhanced performance. The roughness and crystallinity of perovskite film were improved by regulating the heating treatment of substrates. And the perovskite film exhibited largely rise in luminescence, with decreasing defect density. Consequently, with the optimized temperature, the green PeLEDs exhibited 100-fold improvement of external quantum efficiency (EQE) with the luminance of up to 11 941 cd/m2, and the full width at half-maximum (FWHM) of the electroluminescence (EL) spectra was decreased from 25 to 17 nm. At the same time, the red and blue PeLEDs also exhibited obvious enhancement in EQE and luminance by HAVD method, and both the FWHM of EL spectra dropped below 20 nm, exhibiting excellent high color purity. HAVD strategy has a huge potential to be a new commonly used method for low-cost fabrication of displays and lighting.

Designing the Perovskite Structural Landscape for Efficient Blue Emission

Despite the rapid development of perovskite light-emitting diodes (PeLEDs) in recent years, blue PeLEDs’ efficiencies are still inferior to those of their red and green counterparts. The poor perfo...

Colloidal Synthesis of Ternary Copper Halide Nanocrystals for High-Efficiency Deep-Blue Light-Emitting Diodes with a Half-Lifetime above 100 h.

Currently, the blue perovskite light-emitting diodes (PeLEDs) suffer from a compromise in lead toxicity and poor operation stability, and most previous studies have struggled to meet the crucial blue NTSC standard. In this study, electrically driven deep-blue LEDs (∼445 nm) based on zero-dimensional (0D) Cs3Cu2I5 nanocrystals (NCs) were demonstrated with the color coordinates of (0.16, 0.07) and a high external quantum efficiency of ∼1.12%, comparable with the best-performing blue LEDs based on lead-halide perovskites. Encouraged by the remarkable stability of Cs3Cu2I5 NCs against heat and environmental oxygen/moisture, the proposed device was operated in a continuous current mode for 170 h, producing a record half-lifetime of ∼108 h. The device stability was further verified by an aggressive thermal cycling test (300-360-300 K) and a 35-day storage test. Together with the eco-friendly features and facile colloidal synthesis technique, the 0D Cs3Cu2I5 NCs can be therefore regarded as a promising candidate for deep-blue LEDs applications.

Spectral Tuning of Efficient CsPbBrxCl3–x Blue Light-Emitting Diodes via Halogen Exchange Triggered by Benzenesulfonates

CsPbX3 nanocrystal (NC)-based blue perovskite light-emitting diodes (PeLEDs) are still in a backward position while their green and red counterparts have achieved significant progress in the past f...

Chloride Insertion-Immobilization Enables Bright, Narrowband, and Stable Blue-Emitting Perovskite Diodes.

Metal halide perovskites show promise for light-emitting diodes (LEDs) owing to their facile manufacture and excellent optoelectronic performance, including high color purity and spectral stability, especially in the green region. However, for blue perovskite LEDs, the emission spectrum line width is broadened to over 25 nm by the coexistence of multiple reduced-dimensional perovskite domains, and the spectral stability is poor, with an undesirable shift (over 7 nm) toward longer wavelengths under operating conditions, degradation that occurs due to phase separation when mixed halides are employed. Here we demonstrate chloride insertion-immobilization, a strategy that enables blue perovskite LEDs, the first to exhibit narrowband (line width of 18 nm) and spectrally stable (no wavelength shift) performance. We prepare bromide-based perovskites and then employ organic chlorides for dynamic treatment, inserting and in situ immobilizing chlorides to blue-shift and stabilize the emission. We achieve sky-blue LEDs with a record luminance over 5100 cd/m2 at 489 nm, and an operating half-life of 51 min at 1500 cd/m2. By device structure optimization, we further realize an improved EQE of 5.2% at 479 nm and an operating half-life of 90 min at 100 cd/m2.

Bright Blue Light Emission of Ni2+ Ion-Doped CsPbClxBr3-x Perovskite Quantum Dots Enabling Efficient Light-Emitting Devices.

In recent years, significant advances have been achieved in the red and green perovskite quantum dot (PQD)-based light-emitting diodes (LEDs). However, the performances of the blue perovskite LEDs are still seriously lagging behind that of the green and red counterparts. Herein, we successfully developed Ni2+ ion-doped CsPbClxBr3-x PQDs through the room-temperature supersaturated recrystallization synthetic approach. We simultaneously realized the doping of various concentrations of Ni2+ cations and modulated the Cl/Br element ratios by introducing different amounts of NiCl2 solution in the reaction medium. Using the synthetic method, not only the emission wavelength from 508 to 432 nm of Ni2+ ion-doped CsPbClxBr3-x QDs was facially adjusted, but also the photoluminescence quantum yield (PLQY) of PQDs was greatly improved due to efficient removal of the defects of the PQDs. Thus, the blue emission at 470 nm with PLQY of 89% was achieved in 2.5% Ni2+ ion-doped CsPbCl0.99Br2.01 QDs, which increased nearly three times over that of undoped CsPbClBr2 QDs and was the highest for the CsPbX3 PQDs with blue emission, fulfilling the National Television System Committee standards. Benefiting from the highly luminous Ni2+ ion-doped PQDs, the blue-emitting LED at 470 nm was obtained, exhibiting an external quantum efficiency of 2.4% and a maximum luminance of 612 cd/m2, which surpassed the best performance reported previously for the corresponding blue-emitting PQD-based LED.

Halide Homogenization for High-Performance Blue Perovskite Electroluminescence.

Metal halide perovskite light-emitting diodes (LEDs) have achieved great progress in recent years. However, bright and spectrally stable blue perovskite LED remains a significant challenge. Three-dimensional mixed-halide perovskites have potential to achieve high brightness electroluminescence, but their emission spectra are unstable as a result of halide phase separation. Here, we reveal that there is already heterogeneous distribution of halides in the as-deposited perovskite films, which can trace back to the nonuniform mixture of halides in the precursors. By simply introducing cationic surfactants to improve the homogeneity of the halides in the precursor solution, we can overcome the phase segregation issue and obtain spectrally stable single-phase blue-emitting perovskites. We demonstrate efficient blue perovskite LEDs with high brightness, e.g., luminous efficacy of 4.7, 2.9, and 0.4 lm W−1 and luminance of over 37,000, 9,300, and 1,300 cd m−2 for sky blue, blue, and deep blue with Commission Internationale de l'Eclairage (CIE) coordinates of (0.068, 0.268), (0.091, 0.165), and (0.129, 0.061), respectively, suggesting real promise of perovskites for LED applications.