Pr3+掺杂铯铅卤钙钛矿量子点的稳定可调色蓝光发射

卤化钙钛矿型发光二极管(PeLED)的窄发射峰有望用于下一代显示器和照明,但是能量转换效率特别是蓝色PeLED的转换效率仍然低于常规无机和有机LED的效率。在这些钙钛矿中用毒性较小的元素(通常是过渡金属和各种镧系元素)取代Pb,可在保持窄的发射特性的同时提高能源效率。本文介绍了Pr³⁺掺杂与Cl-Br卤化物交换结合的效果,产生了一系列蓝色发射量子点,峰值波长可在430~490 nm范围内可调,这些蓝色Pr³⁺-CsPb(Br/Cl)3量子点的光致发光量子产率(PLQY)比未掺杂Pr³⁺的量子点相比提高了2~3倍。本文还研究了Pr³⁺掺杂蓝光量子点在365 nm紫外线照射下和高温加热时的稳定性,掺杂后的蓝光量子点的光热稳定性提升。     

Efficient and Spectrally Stable Blue Perovskite Light‐Emitting Diodes Based on Potassium Passivated Nanocrystals

Metal halide perovskites have aroused tremendous interest in the past several years for their promising applications in display and lighting. However, the development of blue perovskite light‐emitting diodes (PeLEDs) still lags far behind that of their green and red cousins due to the difficulty in obtaining high‐quality blue perovskite emissive layers. In this study, a simple approach is conceived to improve the emission and electrical properties of blue perovskites. By introducing an alkali metal ion to occupy some sites of peripheral suspended organic ligands, the nonradiative recombination is suppressed, and, consequently, blue CsPb(Br/Cl)₃ nanocrystals with a high photoluminescence quantum efficiency of 38.4% are obtained. The introduced K⁺ acts as a new type of metal ligand, which not only suppresses nonradiative pathways but also improves the charge carrier transport of the perovskite nanocrystals. With further engineering of the device structure to balance the charge injection rate, a spectrally stable and efficient blue PeLED with a maximum external quantum efficiency of 1.96% at the emission peak of 477 nm is fabricated.     

Synergistic Effect of Dual Ligands on Stable Blue Quasi‐2D Perovskite Light‐Emitting Diodes

Since the emergence of inorganic–organic hybrid perovskites a few years ago, there have been many promising achievements in the field of green and red perovskite light‐emitting diodes (PeLEDs). Nevertheless, the performance of blue‐light PeLEDs faces challenges. In this work, the unique synergy obtained by introducing two different ligands to successfully form quasi‐2D perovskite films, which can exhibit stable blue‐light emission, is utilized. The fabricated PeLEDs have a maximum external quantum efficiency of 2.62% and a half lifetime (T₅₀) of 8.8 min. Meanwhile, the electroluminescence spectrum with its peak located at 485 nm, demonstrates improved stability by applying different voltage bias. The finding in this work offers a new way to achieve steady blue PeLEDs with high performance.     

Solvent‐Polarity‐Engineered Controllable Synthesis of Highly Fluorescent Cesium Lead Halide Perovskite Quantum Dots and Their Use in White Light‐Emitting Diodes

Cesium lead halide quantum dots (QDs) have tunable photoluminescence that is capable of covering the entire visible spectrum and have high quantum yields, which make them a new fluorescent materials for various applications. Here, the synthesis of CsPbX₃ (X = Cl, Br, I, or mixed Cl/Br and Br/I) QDs by direct ion reactions in ether solvents is reported, and for the first time the synergetic effects of solvent polarity and reaction temperature on the nucleation and growth of QDs are demonstrated. The use of solvent with a low polarity enables controlled growth of QDs, which facilitates the synthesis of high‐quality CsPbX₃ QDs with broadly tunable luminescence, narrow emission width, and high quantum yield. A QD white LED (WLED) is demonstrated by coating the highly fluorescent green‐emissive CsPbBr₃ QDs together with red phosphors on a blue InGaN chip, which presents excellent warm white light emission with a high rendering index of 93.2 and color temperature of 5447 K, suggesting the potential applications of highly fluorescent cesium lead halide perovskite QDs as an alternative color converter in the fabrication of WLEDs.     

Domain Distribution Management of Quasi-2D Perovskites toward High-Performance Blue Light-Emitting Diodes

Quasi-2D perovskites, as one of the promising materials applied in perovskite light-emitting diodes (PeLEDs), have attracted great attention for their superior semiconductor properties. The inherent multiquantum well structure can induce a strong confinement effect, which is especially suitable for blue emission. However, compared to their green counterparts, blue emitters constructed from quasi-2D perovskites are more sensitive to n domain distribution (where n represents the number of PbX₆ inorganic layers). Suffering from inefficient domain distribution management, blue PeLEDs now face a variety of negative issues, including color instability, multipeak emission, and poor fluorescence yield. In this review, the development of blue PeLEDs and the optical properties of quasi-2D perovskites are overviewed. Then, a classification and summary of strategies for domain distribution management are proposed. Finally, the challenges and potential directions of domain distribution management in quasi-2D perovskites are summarized. This review is expected to provide a comprehensive perspective and reference on domain distribution management toward efficient blue quasi-2D PeLEDs.     

Efficient Blue Perovskite Light‐Emitting Diodes Boosted by 2D/3D Energy Cascade Channels

Lead halide perovskite, as an emerging semiconductor, provides a fire‐new opportunity for high‐definition display and solid‐state lighting. Earthshaking improvements are implemented in green, red, and near‐infrared perovskite light‐emitting diodes (PeLEDs). However, blue PeLEDs are still far behind in performance, which restricts the development of PeLEDs in practical applications. Herein, a facile energy cascade channel strategy via one‐step self‐organized and controllable 2D/3D perovskite preparation by introducing guanidine hydrobromide (GABr) is developed that greatly improves the efficiency of blue PeLEDs. The 2D/3D perovskite structure boosts the energy cascade to induce energy transfer from the wide into the narrow bandgap domains and inhibit free charge diffusion, which increases the density of electrons and holes, and enhances the radiative recombination. Profiting from this energy cascade channels, the external quantum efficiency of blue PeLEDs, emitting at 492 nm, is considerably enhanced from 1.5% of initial blue device to 8.2%. In addition, device operating stability under ambient conditions is also improved by 2.6‐fold. The one‐step self‐organized 2D/3D hybrid perovskites induced by GABr pave a new and simple route toward high‐performance blue emission PeLEDs.     

High-Performance Perovskite-Based Blue Light-Emitting Diodes with Operational Stability by Using Organic Ammonium Cations as Passivating Agents

Blue emissive perovskites can be prepared by incorporating chlorine into bromine-based perovskites to tune their bandgap. However, mixed-halide perovskites exhibit intrinsic phase instability, particularly under electrical potential, owing to halide migration. To achieve high-performance blue perovskite-based light-emitting diodes (PeLEDs) with operational stability, organic ammonium cations are used for passivating the anionic defects of the CsPbBr₂Cl film. Diphenylpropylammonium chloride (DPPACl), used as a passivating agent, successfully prevents the spectral instability of blue PeLEDs by passivating the Cl⁻ vacancies. Consequently, the blue PeLED prepared with this passivating agent delivers excellent device performance with a maximum external quantum efficiency of 3.03%. Moreover, upon tuning the DPPACl concentration, the PeLED emits stably in the deep-blue spectral region (464 nm) with a half-life time of 420 s. Thus, the use of organic ammonium cation as a passivating agent is an effective strategy for developing high-performance blue PeLEDs with operational stability.     

Highly Efficient Blue Light-Emitting Diodes Based on Perovskite Film with Vertically Graded Bandgap and Organic Grain Boundary Passivation Shells

Metal halide perovskite materials have emerged as a promising class of semiconductors for high-performance optoelectronic applications, particularly for light-emitting diodes (LEDs), due to their high quantum efficiency, facile color tunability, narrow emission line widths, as well as cost-effectiveness. Despite the great successes on green and red perovskite LEDs (PeLEDs), the external quantum efficiency (EQE) of blue PeLEDs still lags far behind that of green and red counterparts. Here, wavelength tunable pure and deep blue PeLEDs with high EQE are presented, achieving 17.5% and 10.8% for emission wavelengths of 472 and 461 nm, respectively. The wavelength tenability and high EQE are attributed to the unique vertically graded bandgaps and grain boundary organic shells in the perovskite films. The results demonstrate a significant performance improvement in blue PeLEDs, provide a novel route to fabricate high-performance pure and deep blue PeLEDs that can match the performance of the green and red PeLEDs for future lighting and display applications.     

Metal Halide Perovskite Light‐Emitting Devices: Promising Technology for Next‐Generation Displays

As the requirements and expectation for displays in society are growing, higher standards of the display technology are proposed, including wider color gamut, higher color purity, and higher resolution. The recent emergence of light‐emitting halide perovskites has come with numerous advantages, such as high charge‐carrier mobility, tunable emission wavelength, narrow emission linewidth, and intrinsically high photoluminescence quantum yield. Recent advancement of perovskite‐based light‐emitting diodes (PeLEDs) as a promising technology for next‐generation displays is reviewed. Here, how the attractive optical and electrical properties of perovskite materials can be translated into high PeLED performance are discussed, and working mechanisms and optimization approaches of both perovskite materials and the respective devices are analyzed. On the material side this includes the control of size and composition of perovskites grains and nanocrystals, surface and interface passivation, doping and alloying, while on the device side this includes the interfacial engineering and energy level adjustments, and photon emission enhancement. Several challenges such as performance of blue PeLEDs, the environmental and operational stability of PeLEDs, and the toxicity issues of lead halide perovskites are discussed, and perspectives on future developments of perovskite materials and PeLEDs for the display technology are offered.     

Mixed Ruddlesden–Popper and Dion–Jacobson Phase Perovskites for Stable and Efficient Blue Perovskite LEDs

Producing efficient blue and deep blue perovskite LEDs (PeLEDs) still represents a significant challenge in optoelectronics. Blue PeLEDs still have problems relating to color, luminance, and structural and electrical stability so new materials are needed to achieve better performance. Recent reports suggest using low n states (n = 1, 2, 3) to achieve blue electroluminescence in Ruddlesden–Popper (RP) perovskite films. However, there are fewer reports on the other quasi-2D structure, Dion–Jacobson (DJ) perovksites, despite their highly desirable optical properties, due to the difficulty in achieving charge injection. To resolve this issue, herein, w e have mixed DJ phase precursors, propane-1,3-diammonium (PDA) bromide into RP phase perovskites and fabricated low-dimensional PeLEDs. It is found that these specific precursors aid in suppressing both the low n (n = 1) and high n (n ≥ 4) quasi-2D RP phases and is an effective strategy in blue-shifting sky-blue RP perovskites into the sub-470 nm region. With optimization of the PDA concentration and device layers, it is achieved an external quantum efficiency of 1.5% at 469 nm and stable electroluminescence for the first deep blue PeLED to be reported using DJ perovskites.     

Suppressing Ion Migration of Mixed-Halide Perovskite Quantum Dots for High Efficiency Pure-Red Light-Emitting Diodes

Perovskite-based light-emitting diodes (PeLEDs) with a mixed halide composition can be used to obtain the “pure red” emission, i.e., in the 620–650 nm range, required for high-definition displays. However, fast halide ion migration induces phase separation in these materials under electric fields, resulting in poor spectral stability and low efficiency. Herein, a method for producing mixed halide CsPbI_3-xBr_x quantum dots (QDs) is reported in which ion migration is suppressed. The mixed halide composition is first achieved by anion exchange between CsPbI₃ QDs and hydrobromic acid (HBr), during that the bromine ions efficiently passivate the iodine vacancies of the QDs. The original oleic acid ligands are then exchanged for 1-dodecanethiol (1-DT), which suppresses halide ion migration via the strong binding of the sulfhydryl group with the QD surface. PeLEDs based on these QDs exhibit a pure-red electroluminescence (EL) peak at 637 nm, a maximum external quantum efficiency (EQE) of 21.8% with an average value of 20.4%, a peak luminance of 2653 cd m⁻², and low EQE decease with increasing luminance. The EL spectrum of these devices is stable even at 6.7 V and they have an EQE half-life of 70 min at an initial luminance of 150 cd m⁻².     

Interfacial Nucleation Seeding for Electroluminescent Manipulation in Blue Perovskite Light-Emitting Diodes

Efficient and stable blue emission of perovskite light-emitting diodes (PeLEDs) is a requisite toward their potential applications in full-color displays and solid-state lighting. Rational manipulation over the entire electroluminescence process is promising to break the efficiency limit of blue PeLEDs. Herein, a facile device architecture is proposed to achieve efficient blue PeLEDs for simultaneously reducing the energetic loss during electron-photon conversion and boosting the light outcoupling. Effective interfacial engineering is employed to manipulate the perovskite crystallization nucleation, enabling highly compact perovskite nanocrystal assemblies and suppressing the trap-induced carrier losses by means of interfacial hydrogen bonding interactions. This strategy contributes to a high external quantum efficiency (EQE) of 12.8% for blue PeLEDs emitting at 486 nm as well as improved operational stability. Moreover, blue PeLEDs reach a peak EQE of 16.8% with the incorporation of internal outcoupling structures for waveguided light, which can be further raised to 27.5% by integrating a lens-based structure for substrate-mode light. These results verify the validity of this strategy in producing efficient and stable blue PeLEDs for practical applications.     

Strategies Toward Efficient Blue Perovskite Light-Emitting Diodes

Substantial progress has been made in blue perovskite light-emitting diodes (PeLEDs). In this review, the strategies for high-performance blue PeLEDs are described, and the main focus is on the optimization of the optical and electrical properties of perovskites. In detail, the fundamental device working principles are first elucidated, followed by a systematical discussion of the key issues for achieving high-quality perovskite nanocrystals (NCs) and quasi-2D perovskites. These involve ligand optimization and metal doping in enhancing the carrier transport and reducing the traps of perovskite NCs, as well as the perovskite phase modulation and defect passivation in improving energy transfer and emission efficiency of quasi-2D perovskites. The strategies for efficient 3D mixed-halide perovskite and lead-free perovskite blue LEDs are then briefly introduced. After that, other strategies, including effective charge transport layer, efficient perovskite emission system, and effective device architecture for high light outcoupling efficiency, are further discussed to boost the blue PeLED performances. Meanwhile, the testing standard of blue PeLED lifetime is suggested to enable the direct comparisons of the device operational stability. Finally, challenges and future directions for blue PeLEDs are addressed.     

Band Edge Control of Quasi-2D Metal Halide Perovskites for Blue Light-Emitting Diodes with Enhanced Performance

Perovskite light-emitting diodes (PeLEDs) have received great attention for their potential as next-generation display technology. While remarkable progress has been achieved in green, red, and near-infrared PeLEDs with external quantum efficiencies (EQEs) exceeding 20%, obtaining high performance blue PeLEDs remains a challenge. Poor charge balance due to large charge injection barriers in blue PeLEDs has been identified as one of the major roadblocks to achieve high efficiency. Here band edge control of perovskite emitting layers for blue PeLEDs with enhanced charge balance and device performance is reported. By using organic spacer cations with different dipole moments, that is, phenethyl ammonium (PEA), methoxy phenethyl ammonium (MePEA), and 4-fluoro phenethyl ammonium (4FPEA), the band edges of quasi-2D perovskites are tuned without affecting their band gaps. Detailed characterization and computational studies have confirmed the effect of dipole moment modification to be mostly electrostatic, resulting in changes in the ionization energies of ≈0.45 eV for MePEA and ≈ −0.65 eV for 4FPEA based thin films relative to PEA-based thin films. With improved charge balance, blue PeLEDs based on MePEA quasi-2D perovskites show twofold increase of the EQE as compared to the control PEA based devices.     

A recent advances of blue perovskite light emitting diodes for next generation displays

The halide perovskite blue light emitting diodes (PeLEDs) attracted many researchers because of its fascinating opto-electrical properties.This review introduces the recent progress of blue PeLEDs which focuses on emissive layers and interlay-ers.The emissive layer covers three types of perovskite structures:perovskite nanocrystals (PeNCs),2-dimensional (2D) and quasi-2D perovskites,and bulk (3D) perovskites.We will discuss about the remaining challenges of blue PeLEDs,such as lim-ited performances,device instability issues,which should be solved for blue PeLEDs to realize next generation displays.     

Solvothermal Synthesis of High‐Quality All‐Inorganic Cesium Lead Halide Perovskite Nanocrystals: From Nanocube to Ultrathin Nanowire

Recently, all‐inorganic cesium lead halide (CsPbX₃, X = Cl, Br, I) perovskite nanocrystals have drawn much attention because of their outstanding photophysical properties and potential applications. In this work, a simple and efficient solvothermal approach to prepare CsPbX₃ nanocrystals with tunable and bright photoluminescent (PL) properties, controllable composition, and morphology is presented. CsPbX₃ nanocubes are successfully prepared with bright emission high PL quantum yield up to 80% covering the full visible range and narrow emission line widths (from 12 to 36 nm). More importantly, ultrathin CsPbX₃ (X = Cl/Br, Br, and Br/I) nanowires (with diameter as small as ≈2.6 nm) can be prepared in a very high morphological yield (almost 100%). A strong quantum confinement effect is observed in the ultrathin nanowires, in which both the absorption and emission peaks shift to shorter wavelength range compared to their bulk bandgap. The reaction parameters, such as temperature and precursors, are varied to investigate the growth process. A white light‐emitting device prototype device with wide color gamut covering up to 120% of the National Television System Committee standard has been demonstrated by using CsPbBr₃ nanocrystals as the green light source. The method in this study provides a simple and efficient way to prepare high‐quality CsPbX₃ nanocrystals.     

Pure Blue Electroluminescence by Differentiated Ion Motion in a Single Layer Perovskite Device

Blue electroluminescence is highly desired for emerging light-emitting devices for display applications and optoelectronics in general. However, saturated, efficient, and stable blue emission has been challenging to achieve, particularly in mixed-halide perovskites, where intrinsic ion motion and halide segregation compromises spectral purity. Here, CsPbBr_3−xCl_x perovskites, polyelectrolytes, and a salt additive are leveraged to demonstrate pure blue emission from single-layer light-emitting electrochemical cells (LECs). The electrolytes transport the ions from salt additives, enhancing charge injection and stabilizing the inherent perovskite emissive lattice for highly pure and sustained blue emission. Substituting Cl into CsPbBr₃ tunes the perovskite luminescence from green through blue. Sky blue and saturated blue devices produce International Commission on Illumination coordinates of (0.105, 0.129) and (0.136, 0.068), respectively, with the latter meeting the US National Television Committee standard for the blue primary. Likewise, maximum luminances of 2900 and 1000 cd m⁻², external quantum efficiencies (EQEs) of 4.3% and 3.9%, and luminance half-lives of 5.7 and 4.9 h are obtained for sky blue and saturated blue devices, respectively. Polymer and LiPF₆ inclusion increases photoluminescence efficiency, suppresses halide segregation, induces thin-film smoothness and uniformity, and reduces crystallite size. Overall, these devices show superior performance among blue perovskite light-emitting diodes (PeLEDs) and general LECs.     

Tuning the performance of hybrid organic/inorganic quantum dot light-emitting devices

The luminescence of inorganic core-shell semiconductor nanocrystal quantum dots (QDs) can be tuned across much of the visible spectrum by changing the size of the QDs while preserving a spectral full width at half maximum (FWHM) as narrow as 30 nm and photoluminescence efficiency of 50% [Journal of Physical Chemistry B 101 (46) (1997) 9463] [1]. Organic capping groups, surrounding the QD lumophores, facilitate processing in organic solvents and their incorporation into organic thin film light-emitting device (LED) structures [Nature 370 (6488) (1994) 354] [2]. A recent study has shown that hybrid organic/inorganic QD-LEDs can indeed be fabricated with high brightness and small spectral FWHM, utilizing a phase segregation process which self-assembles CdSe(ZnS) core(shell) QDs onto an organic thin film surface [Nature 420 (6917) (2002) 800] [3]. We now demonstrate that the phase segregation process can be generally applied to the fabrication of QD-LEDs containing a wide range of CdSe particle sizes and ZnS overcoating thicknesses. By varying the QD core diameter from 32 Å to 58 Å, we show that peak electroluminescence is tuned from 540 nm to 635 nm. Increase in the QD shell thickness to 2.5 monolayers (∼0.5 nm) improves the LED external quantum efficiency, consistent with a Förster energy transfer mechanism of generating QD excited states. In this work we also identify the challenges in designing devices with very thin (∼5 nm thick) emissive layers [Chemical Physics Letters 178 (5–6) (1991) 488] [4], emphasizing the increased need for precise exciton confinement. In both QD-LEDs and archetypical all-organic LEDs with thin emissive layers, we show that there is an increase in the exciton recombination region width as the drive current density is increased. Overall, our study demonstrates that integration of QDs into organic LEDs has the potential to enhance the performance of thin film light emitters, and promises to be a rich field of scientific endeavor.     

Enhanced performance of spectra stable blue perovskite light-emitting diodes through Poly(9-vinylcarbazole) interlayer incorporation

Since the emergence of organic-inorganic hybrid perovskites, the development of perovskite light-emitting diodes (PeLEDs) with green/red emission have made great progress, and the corresponding external quantum efficiency (EQE) has exceeded 20%. However, the research progress of blue-emitting PeLED still has certain challenges. In this article, a multi-cation per-bromine perovskite film is prepared by introducing polymer molecules poly(9-vinylcarbazole) (PVK) in an anti-solvent (chloroform). When the concentration of PVK is optimized to 0.1 mg/mL, a smooth, dense, high-quality film with photoluminescence quantum efficiency (PLQY) up to 20.70% is obtained. The introduction of PVK can assist the formation of perovskite films for interface modification via surface defect passivation. The optimized blue PeLED has a maximum brightness of 3136 cd/m² and a maximum EQE of 3.49% at 488 nm. More importantly, the optimized blue PeLED has excellent color stability under high applied voltage up to 12 V or continuous operation.     

Phase Aggregation Suppression of Homogeneous Perovskites Processed in Ambient Condition toward Efficient Light-Emitting Diodes

Perovskite light-emitting diodes (PeLEDs) have attracted attention because of their high efficiencies. However, due to the sensitivity of perovskites to ambient condition, perovskite emitter layers are generally fabricated under an inert gas environment (e.g., dry N₂), which increases processing complexity and cost. Here, air-prepared quasi-2D perovskites are reported for efficient PeLEDs. It is found that the phase aggregation is the major obstacle deteriorating the characteristics of air-prepared perovskites. Through antisolvent engineering to modulate the nucleation and growth characteristics of perovskite films from precursor solution, phase aggregations are restrained. Confocal laser scanning fluorescence microscopy results demonstrate homogeneous perovskite films with uniform photoluminescence distributions. Traps at grain boundaries are passivated, and exciton transfer among perovskite phases becomes effective. Finally, efficient green PeLEDs based on air-prepared perovskites are realized with an external quantum efficiency of 15.4%. This work provides a promising strategy to fabricate cost-effective perovskite devices in ambient air condition.