Highly Efficient Perovskite Light-Emitting Diodes Incorporating Full Film Coverage and Bipolar Charge Injection

Progress and Application of Halide Perovskite Materials for Solar Cells and Light Emitting Devices

Halide perovskite materials have attracted worldwide attention in the photovoltaic area due to the rapid improvement in efficiency, from less than 4% in 2009 to 26.1% in 2023 with only a nanometer lever photo-active layer. Meanwhile, this nova star found applications in many other areas, such as light emitting, sensor, etc. This review started with the fundamentals of physics and chemistry behind the excellent performance of halide perovskite materials for photovoltaic/light emitting and the methods for preparing them. Then, it described the basic principles for solar cells and light emitting devices. It summarized the strategies including nanotechnology to improve the performance and the application of halide perovskite materials in these two areas: from structure-property relation to how each component in the devices affects the overall performance. Moreover, this review listed the challenges for the future applications of halide perovskite materials.

Superior External Quantum Efficiency of LEDs via Quasi-2D Perovskite Crystals Implanted with Phenethylammonium Acetate

The multiple quantum well structure of a quasi-two-dimensional (quasi-2D) perovskite leads to nonradiative Auger recombination (AR). This is due to high local carrier density in recombination centers, although the radiative recombination is improved by efficient energy transfer. In this study, we suppress the AR by introducing phenethylammonium acetate (PEAAc) into the quasi-2D PEA₂Cs_n-1Pb_nBr_3n+1 perovskite. The recombination centers of n ≥ 4 phases can be promoted because the COO^- preferentially coordinates with Pb²⁺_, inhibiting the fast formation of n = 1, 2, 3 phases with phenethylammonium anion (PEA⁺). Thus, the AR is suppressed due to the lower density of local charge carriers. To balance the AR suppression and decreasing binding energy in promoting the n ≥ 4 phases, the PEAAc:PEABr molar ratios are adjusted. At the optimal molar ratio, perovskite light-emitting diodes (PeLEDs) with a maximum luminescence of ∼29942 cd m^-2 and a maximum external quantum efficiency of ∼20.2% are achieved. These results confirm the most efficient PeLEDs based on PEA₂Cs_n-1Pb_nBr_3n+1 without passivation. Moreover, the efficiency roll off is significantly mitigated with a high threshold of over 3.51 mA/cm². This study develops high-efficiency PeLEDs with a low efficiency rolloff.

Highly Efficient Quasi-2D Perovskite Light-Emitting Diodes Incorporating a TADF Dendrimer as an Exciton-Retrieving Additive

Although small organics or polymer additives have been introduced to enhance film formation and radiative recombination of perovskite light-emitting diodes (PeLEDs), the exciton utilization and quantum efficiency need further optimization. Here, we introduce a thermal-activated delayed fluorescence (TADF) dendrimer as an additive to enhance the surface coverage and reduce the trap state of the grain boundary. More importantly, the TADF nature of such an additive can retrieve the exciton dissociated from perovskite or trapped by the grain boundary and then transfer the energy back to emissive perovskite through the Förster energy transfer process. Since the triplets can be reused by reverse intersystem crossing in such a TADF additive, the theoretical exciton utilization is 100%. As a result, the optimized PeLEDs cooperating with a TADF additive achieved a high current efficiency of 39.0 cd A^-1 and an ultrabright luminescence of 18,000 cd m^-2, which are almost 5 times higher than those of the control device without an additive. Moreover, the device stability monitored by half-lifetime at 1000 cd m^-2 enhanced 2 times after introducing the TADF dendrimer as an additive. The parent dendrimer without a TADF feature was also synthesized as an additive to explore the mechanism action, which found that 54% enhancement of device efficiency can be attributed to defect passivating, while 46% was assigned to retrieved energy. This research first demonstrates that the TADF dendrimer is a promising exciton-retrieving additive for enhancing the performance of PeLEDs by passivating defect, filling up grain boundary, and retrieving leakage exciton.

Realizing CsPbBr3 Light-Emitting Diode Arrays Based on PDMS Template Confined Solution Growth of Single-Crystalline Perovskite

Metal-halide perovskites have shown excellent optoelectronic properties, among which the array-type architecture is highly desirable. However, both the susceptibility of perovskites to polar solvents and the complex 3D geometry of array structure have led to great challenges for device fabrication and performance, which hinders their further applications. Here, we report a simple but efficient approach highly compatible with the state-of-the-art microelectronics processes to construct single-crystalline array light-emitting diodes (LEDs) of perovskite. The well-aligned single-crystalline array was sandwiched as the emission layer, among the carefully designed multilayer ITO/NiO/CsPbBr₃/PMMA/ZnO/Ag structure. Through systematically altering the size of CsPbBr₃ single crystal and the thickness of insulation layer, the device performance has been optimized and eventually achieved a 99% working ratio in a 62 × 47 array. Moreover, a prototype device of LED display was also fabricated. These results clearly demonstrate that our strategy is efficient, reliable, and versatile, which can be easily extended to other perovskites.

Synthesis conditions influencing formation of MAPbBr3 perovskite nanoparticles prepared by the ligand-assisted precipitation method

This work reports on an optimized procedure to synthesize methylammonium bromide perovskite nanoparticles. The ligand-assisted precipitation synthetic pathway for preparing nanoparticles is a cost-effective and promising method due to its ease of scalability, affordable equipment requirements and convenient operational temperatures. Nevertheless, there are several parameters that influence the resulting optical properties of the final nanomaterials. Here, the influence of the choice of solvent system, capping agents, temperature during precipitation and ratios of precursor chemicals is described, among other factors. Moreover, the colloidal stability and stability of the precursor solution is studied. All of the above-mentioned parameters were observed to strongly affect the resulting optical properties of the colloidal solutions. Various solvents, dispersion media, and selection of capping agents affected the formation of the perovskite structure, and thus qualitative and quantitative optimization of the synthetic procedure conditions resulted in nanoparticles of different dimensions and optical properties. The emission maxima of the nanoparticles were in the 508–519 nm range due to quantum confinement, as confirmed by transmission electron microscopy. This detailed study allows the selection of the best optimal conditions when using the ligand-assisted precipitation method as a powerful tool to fine-tune nanostructured perovskite features targeted for specific applications.

Efficient All-Inorganic Perovskite Light-Emitting Diodes with Cesium Tungsten Bronze as a Hole-Transporting Layer

The realization of high-performance optoelectronic devices requires excellent charge-transporting layers and efficient carrier recombination. Herein, we synthesized cesium tungsten bronze (Cs_0.32WO₃) nanocrystals and utilized them as the hole-transporting material to fabricate all-inorganic perovskite light-emitting diodes (PeLEDs). Due to the excellent carrier balance characteristics via comparison between the hole-only device and electron-only device, the all-inorganic PeLEDs with CsPbBr₃ as the light-emitting layer present the maximum current efficiency of 31.51 cd/A and external quantum efficiency (EQE) of 8.48%, which are self-evidently enhanced compared with the PEDOT:PSS (14.78 cd/A, 4.03%) and WO₃ (24.75 cd/A, 6.18%) based devices. Considering the remarkably improved device performance, the proposed HTL of Cs_0.32WO₃ is promising, acting as a favorable building block for high-efficiency light-emitting devices.

Emergence of Impurity-Doped Nanocrystal Light-Emitting Diodes

In recent years, impurity-doped nanocrystal light-emitting diodes (LEDs) have aroused both academic and industrial interest since they are highly promising to satisfy the increasing demand of display, lighting, and signaling technologies. Compared with undoped counterparts, impurity-doped nanocrystal LEDs have been demonstrated to possess many extraordinary characteristics including enhanced efficiency, increased luminance, reduced voltage, and prolonged stability. In this review, recent state-of-the-art concepts to achieve high-performance impurity-doped nanocrystal LEDs are summarized. Firstly, the fundamental concepts of impurity-doped nanocrystal LEDs are presented. Then, the strategies to enhance the performance of impurity-doped nanocrystal LEDs via both material design and device engineering are introduced. In particular, the emergence of three types of impurity-doped nanocrystal LEDs is comprehensively highlighted, namely impurity-doped colloidal quantum dot LEDs, impurity-doped perovskite LEDs, and impurity-doped colloidal quantum well LEDs. At last, the challenges and the opportunities to further improve the performance of impurity-doped nanocrystal LEDs are described.

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 CsPbCl_xBr_3-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 CsPbCl_xBr_3-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 CsPbCl_0.99Br_2.01 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.

Interface and Defect Engineering for Metal Halide Perovskite Optoelectronic Devices

Metal halide perovskites have been in the limelight in recent years due to their enormous potential for use in optoelectronic devices, owing to their unique combination of properties, such as high absorption coefficient, long charge-carrier diffusion lengths, and high defect tolerance. Perovskite-based solar cells and light-emitting diodes (LEDs) have achieved remarkable breakthroughs in a comparatively short amount of time. As of writing, a certified power conversion efficiency of 22.7% and an external quantum efficiency of over 10% have been achieved for perovskite solar cells and LEDs, respectively. Interfaces and defects have a critical influence on the properties and operational stability of metal halide perovskite optoelectronic devices. Therefore, interface and defect engineering are crucial to control the behavior of the charge carriers and to grow high quality, defect-free perovskite crystals. Herein, a comprehensive review of various strategies that attempt to modify the interfacial characteristics, control the crystal growth, and understand the defect physics in metal halide perovskites, for both solar cell and LED applications, is presented. Lastly, based on the latest advances and breakthroughs, perspectives and possible directions forward in a bid to transcend what has already been achieved in this vast field of metal halide perovskite optoelectronic devices are discussed.

Strategies to Improve Luminescence Efficiency of Metal-Halide Perovskites and Light-Emitting Diodes

Metal-halide perovskites (MHPs) are well suited to be vivid natural color emitters due to their superior optical and electrical properties, such as narrow emission linewidths, easily and widely tunable emission wavelengths, low material cost, and high charge carrier mobility. Since the first development of MHP light-emitting diodes (PeLEDs) in 2014, many researchers have tried to understand the properties of MHP emitters and the limitations to luminescence efficiency (LE) of PeLEDs, and have devoted efforts to increase the LE of MHP emitters and PeLEDs. Within three and half years, PeLEDs have shown rapidly increased LE from external quantum efficiency ≈0.1% to ≈14.36%. Herein, the factors that limit the LE of PeLEDs are reviewed; the factors are characterized into the following groups: i) photophysical properties of MHP crystals, ii) morphological factors of MHP layers, and iii) problems caused by device architectures. Then, the strategies to overcome those luminescence-limiting factors in MHP emitters and PeLEDs are critically evaluated. Finally, research directions to further increase the LE of MHP emitters and the potential of MHPs as a core component in next-generation displays and solid-state lightings are suggested.

Enhanced Performance of Perovskite Light-Emitting Diodes via Diamine Interface Modification

Interfacial engineering between charge transport layers and perovskite light-emitting layers has been applied as an effective strategy to enhance performance of perovskite light-emitting diodes (PeLEDs). Herein, we introduce a Lewis base diamine molecule [2,2-(ethylenedioxy)bis(ethylammonium), EDBE] to modify the interface between the ZnMgO electron transport layer (ETL) and perovskite light-emitting layer in PeLEDs. With two amino groups in EDBE, one amine can interact with ZnMgO beneath to tune the growth of perovskite films, resulting in improved electron injection and suppressed current leakage. Meanwhile, the other amine can passivate the surface trap states of the polycrystalline perovskite films, which would eliminate trap-mediated nonradiative recombination. An enhanced performance for near-infrared PeLEDs is achieved with external quantum efficiency from 9.15 to 12.35% after incorporating the EDBE interfacial layer. This work demonstrated that the introduction of Lewis base diamine molecules as the ETL/perovskite interfacial agent is a promising way for developing high-performance PeLEDs.

Effects of n-butyl amine incorporation on the performance of perovskite light emitting diodes

The efficiency of perovskite light emitting diodes (PeLEDs) is crucially limited by leakage current and nonradiative recombination. Here we introduce n-butyl amine (BA) to modulate the growth of perovskite films as well as improve the performance of PeLEDs, and investigate in detail the effects of BA incorporation on the structural, optical, and electrical characteristics of perovskite films. The results indicate that BA would terminate the grain surface and inhibit crystal growth, leading to increased radiative recombination. However, BA overload would make the films loose and recreate shunt paths. The electrical detriment of BA overload outweighs its optical benefit. As a result, optimal PeLEDs can be obtained only with moderate BA incorporation.

Highly Efficient and Stable Inverted Perovskite Solar Cell Obtained via Treatment by Semiconducting Chemical Additive

The addition of chemical additives is considered as a promising approach for obtaining high-quality perovskite films under mild conditions, which is essential for both the efficiency and the stability of organic-inorganic hybrid perovskite solar cells (PeSCs). Although such additive engineering yields high-quality films, the inherent insulating property of the chemical additives prevents the efficient transport and extraction of charge carriers, thereby limiting the applicability of this approach. Here, it is shown that organic conjugated molecules having rhodanine moieties (i.e., SA-1 and SA-2) can be used as semiconducting chemical additives that simultaneously yield large-sized perovskite grains and improve the charge extraction. Using this strategy, a high power conversion efficiency of 20.3% as well as significantly improved long-term stability under humid air conditions is achieved. It is believed that this approach can provide a new pathway to designing chemical additives for further improving the efficiency and stability of PeSCs.

Effect of perovskite film morphology on device performance of perovskite light-emitting diodes

Organic-inorganic hybrid perovskite materials have attracted significant attention in the last few years owing to their high photoluminescence quantum efficiency (PLQE) (of approximately 100%), narrow emission with a low full-width at half maximum (FWHM), and tunable optical bandgaps over the entire visible spectral range. Thus, perovskite materials are regarded as next-generation candidates for light-emitting diode application. Recently, perovskite light-emitting diodes (PeLEDs) with an external quantum efficiency of more than 20% have been successfully fabricated. Moreover, the efficiency and stability of PeLEDs have been significantly improved with the use of high-quality, uniform perovskite films. Here, the recent progress in the morphological control of perovskite films used in PeLEDs is reviewed. The current strategies involved in the morphological control of perovskite films to improve the device performance and long-term stability of PeLEDs via perovskite film modification, interface engineering, and quasi 2D-perovskite, are discussed.

Cesium Lead Chloride/Bromide Perovskite Quantum Dots with Strong Blue Emission Realized via a Nitrate-Induced Selective Surface Defect Elimination Process

Cesium lead halide perovskites emitting blue light in the 460-470 nm range of wavelengths have so far been plagued with rather poor luminescent performance, placing inevitable limitations on the development of perovskite nanocrystal-based blue light-emitting devices. Herein, a selective surface defect elimination process with the help of hydrated nitrates was introduced into the perovskite/toluene solution to strip the undesired surface defects and vacancies and to boost the photoluminescence quantum yield of true-blue-light-emitting (at 466 nm) CsPb(Cl/Br)₃ perovskite nanocrystals to the impressive value of 85%. Unlike the conventional passivation strategy, the anionic nitrate ions are able to desorb the undesired surface metallic lead and combine with excess surface metal ions, leaving perovskite quantum dots with better crystallinity and fewer surface defects.

Electronic and optical properties of perovskite compounds MA1−αFAαPbI3−βXβ (X = Cl, Br) explored for photovoltaic applications

As outstanding light harvesters, solution-processable organic–inorganic hybrid perovskites (OIHPs) have been drawing considerable attention thanks to their higher power conversion efficiency (PCE) and cost-effective synthesis relative to other photovoltaic materials. Nevertheless, their further development is severely hindered by the drawbacks of poor stability and rapid degradation in particular. First-principles calculations based on density functional theory (DFT) are hence performed towards the perovskite compounds MA_1−αFA_αPbI_3−βX_β (X = Cl, Br), with the aim of exploring more efficient and stable OIHPs. In addition to that, a hybrid density functional is adopted for exact electronic properties, and their band structures indicate that the doped series are all direct band-gap semiconductors. Moreover, the defect formation energies indicate that the stability of perovskite compounds can be significantly enhanced via ion doping. Meanwhile, it is unveiled that the optical performance of the doped perovskite series is also effectively improved through ion doping. Therefore, the investigated perovskite compounds MA_1−αFA_αPbI_3−βX_β (X = Cl, Br) are promising candidates for enhancing solar-energy conversion efficiency. Our results pave a way in deeper understanding of the inherent characteristics of OIHPs, which is useful for designing new-type perovskite-based photovoltaic devices.

The absorption performance of perovskite CH₃NH₃PbI₃ can be significantly improved via mono-, or co-doping of organic cations and halide ions.

Improved photoelectric performance of all-inorganic perovskite through different additives for green light-emitting diodes

Improving the performance of all-inorganic CsPbBr₃–PEO–PVP-based LEDs with the structure of ITO/PEDOT:PSS/Perovskite/TPBI/LiF/Al.

Highly bright perovskite light-emitting diodes based on quasi-2D perovskite film through synergetic solvent engineering

Recently, quasi-two dimensional (2D) perovskites have attracted great interest as they can be facilely fabricated and yield high photoluminescence quantum yield. However, the luminance and the efficiency of perovskite light-emitting diodes (PeLEDs) based on quasi-2D perovskites are limited by the carrier transport and the crystallization properties of the quasi-2D perovskite films. Herein, a synergetic solvent engineering approach is proposed to improve the crystallinity and the carrier transport by optimizing the film morphology of the quasi-2D perovskite films. Consequently, the maximum luminance of green PeLEDs based on quasi-2D PEA₂ (MAPbBr₃)₂PbBr₄ perovskite is dramatically enhanced from 4000 cd m⁻² to 18 000 cd m⁻² and the current efficiency increases from 3.40 cd A⁻¹ to 8.74 cd A⁻¹. This work provides a promising way to control the morphology and the crystallinity properties of quasi-2D perovskite films for high-performance optoelectronic devices.

A synergetic solvent engineering approach to improve crystallinity and carrier transport, by optimizing film morphology of the quasi-2D perovskite films.

Perovskites for Light Emission

Next-generation displays require efficient light sources that combine high brightness, color purity, stability, compatibility with flexible substrates, and transparency. Metal halide perovskites are a promising platform for these applications, especially in light of their excellent charge transport and bandgap tunability. Low-dimensional perovskites, which possess perovskite domains spatially confined at the nanoscale, have further extended the degree of tunability and functionality of this materials platform. Herein, the advances in perovskite materials for light-emission applications are reviewed. Connections among materials properties, photophysical and electrooptic spectroscopic properties, and device performance are established. It is discussed how incompletely solved problems in these materials can be tackled, including the need for increased stability, efficient blue emission, and efficient infrared emission. In conclusion, an outlook on the technologies that can be realized using this material platform is presented.

Tunable Hybrid Fano Resonances in Halide Perovskite Nanoparticles

Halide perovskites are known to support excitons at room temperatures with high quantum yield of luminescence that make them attractive for all-dielectric resonant nanophotonics and meta-optics. Here we report the observation of broadly tunable Fano resonances in halide perovskite nanoparticles originating from the coupling of excitons to the Mie resonances excited in the nanoparticles. Signatures of the photon-exciton (" hybrid") Fano resonances are observed in dark-field spectra of isolated nanoparticles, and also in the extinction spectra of aperiodic lattices of such nanoparticles. In the latter case, chemical tunability of the exciton resonance allows reversible tuning of the Fano resonance across the 100 nm bandwidth in the visible frequency range, providing a novel approach to control optical properties of perovskite nanostructures. The proposed method of chemical tuning paves the way to an efficient control of emission properties of on-chip-integrated light-emitting nanoantennas.

All-Solution-Processed Pure Formamidinium-Based Perovskite Light-Emitting Diodes

All-solution-processed pure formamidinium-based perovskite light-emitting diodes (PeLEDs) with record performance are successfully realized. It is found that the FAPbBr₃ device is hole dominant. To achieve charge carrier balance, on the anode side, PEDOT:PSS 8000 is employed as the hole injection layer, replacing PEDOT:PSS 4083 to suppress the hole current. On the cathode side, the solution-processed ZnO nanoparticle (NP) is used as the electron injection layer in regular PeLEDs to improve the electron current. With the smallest ZnO NPs (2.9 nm) as electron injection layer (EIL), the solution-processed PeLED exhibits a highest forward viewing power efficiency of 22.3 lm W^-1 , a peak current efficiency of 21.3 cd A^-1 , and an external quantum efficiency of 4.66%. The maximum brightness reaches a record 1.09 × 10⁵ cd m^-2 . A record lifetime T₅₀ of 436 s is achieved at the initial brightness of 10 000 cd m^-2 . Not only do PEDOT:PSS 8000 HIL and ZnO NPs EIL modulate the injected charge carriers to reach charge balance, but also they prevent the exciton quenching at the interface between the charge injection layer and the light emission layer. The subbandgap turn-on voltage is attributed to Auger-assisted energy up-conversion process.

The Role of Metal Halide Perovskites in Next-Generation Lighting Devices

The development of smart illumination sources represents a central challenge for current technology. In this context, the quest for novel materials that enable efficient light generation is essential. Metal halide compounds with perovskite crystalline structure (ABX₃) have gained tremendous interest in the last five years since they come as easy-to-prepare high performance semiconductors. Perovskite absorbers are driving the power-conversion-efficiencies of thin film photovoltaics to unprecedented values. Nowadays, mixed-cation, mixed-halide lead perovskite solar cells reach efficiencies consistently over 20% and promise to get close to 30% in multijunction devices when combined with silicon cells at no surcharge. Nonetheless, perovskites' fame extends further since extensive research on these novel semiconductors has also revealed their brightest side. Soon after their irruption in the photovoltaic scenario, demonstration of efficient color tunable-with high color purity-perovskite emitters has opened new avenues for light generation applications that are timely to discuss herein.

Highly Efficient Spectrally Stable Red Perovskite Light-Emitting Diodes

Perovskite light-emitting diodes (LEDs) have recently attracted great research interest for their narrow emissions and solution processability. Remarkable progress has been achieved in green perovskite LEDs in recent years, but not blue or red ones. Here, highly efficient and spectrally stable red perovskite LEDs with quasi-2D perovskite/poly(ethylene oxide) (PEO) composite thin films as the light-emitting layer are reported. By controlling the molar ratios of organic salt (benzylammonium iodide) to inorganic salts (cesium iodide and lead iodide), luminescent quasi-2D perovskite thin films are obtained with tunable emission colors from red to deep red. The perovskite/polymer composite approach enables quasi-2D perovskite/PEO composite thin films to possess much higher photoluminescence quantum efficiencies and smoothness than their neat quasi-2D perovskite counterparts. Electrically driven LEDs with emissions peaked at 638, 664, 680, and 690 nm have been fabricated to exhibit high brightness and external quantum efficiencies (EQEs). For instance, the perovskite LED with an emission peaked at 680 nm exhibits a brightness of 1392 cd m^-2 and an EQE of 6.23%. Moreover, exceptional electroluminescence spectral stability under continuous device operation has been achieved for these red perovskite LEDs.

Electrode quenching control for highly efficient CsPbBr3 perovskite light-emitting diodes via surface plasmon resonance and enhanced hole injection by Au nanoparticles

Compared to organic-inorganic hybrid metal halide perovskites, all-inorganic cesium lead halides (e.g, CsPbBr₃) hold greater promise in being emissive materials for light-emitting diodes owing to their superior optoelectronic properties as well as their higher stabilities. However, there is still considerable potential for breakthroughs in the current efficiency of CsPbBr₃ perovskite light-emitting diodes (PeLEDs). Electrode quenching is one of the main problems limiting the current efficiency of PeLEDs when poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) is used as the hole injection layer. In this work, electrode quenching control was realized via incorporating Au NPs into PEDOT:PSS. As a result, the CsPbBr₃ PeLEDs realized an improvement in maximum luminescence ranging from ∼2348 to ∼7660 cd m^-2 (∼226% enhancement) and current efficiency from 1.65 to 3.08 cd A^-1 (∼86% enhancement). Such substantial enhancement of the electroluminescent performance can be attributed to effective electrode quenching control at the PEDOT:PSS/CsPbBr₃ perovskite interface via the combined effects of local surface plasma resonance coupling and enhanced hole transportation in the PEDOT:PSS layer by Au nanoparticles.

Strategy of Solution-Processed All-Inorganic Heterostructure for Humidity/Temperature-Stable Perovskite Quantum Dot Light-Emitting Diodes

Recently, a pressing requirement of solid-state lighting sources with high performance and low cost has motivated increasing research in metal halide perovskites. However, the relatively low emission efficiency and poor operation stability of perovskite light-emitting diodes (LEDs) are still critical drawbacks. In this study, a strategy of solution-processed all-inorganic heterostructure was proposed to overcome the emission efficiency and operation stability issues facing the challenges of perovskite LEDs. Solution-processed n-ZnO nanoparticles and p-NiO are used as the carrier injectors to fabricate all-inorganic heterostructured CsPbBr₃ quantum dot LEDs, and a high-efficiency green emission is achieved with maximum luminance of 6093.2 cd/m², external quantum efficiency of 3.79%, and current efficiency of 7.96 cd/A. More importantly, the studied perovskite LEDs possess a good operation stability after a long test time in air ambient. Typically, the devices can endure a high humidity (75%, 12 h) and a high working temperature (393 K, three heating/cooling cycles) even without encapsulation, and the operation stability is better than any previous reports. It is anticipated that this work will provide an effective strategy for the fabrication of high-performance perovskite LEDs with good stability under ambient and harsh conditions, making practical applications of such LEDs a real possibility.

Interfacial engineering with ultrathin poly (9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) layer for high efficient perovskite light-emitting diodes

Organic-inorganic hybrid perovskites have attracted great attention in the field of lighting and display due to their very high color purity and low-cost solution-process. Researchers have done a lot of work in realizing high performance electroluminescent devices. However, the current efficiency (CE) of methyl-ammonium lead halide perovskite light-emitting diodes (PeLEDs) still needs to be improved. Herein, we demonstrate the enhanced performance of PeLEDs through introducing an ultrathin poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) buffer layer between poly(3,4-ethylendioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and CH₃NH₃PbBr₃ perovskite. Compared to the reference device without PFO, the optimal device luminous intensity, the maximum CE, and the maximum external quantum efficiency increases from 8139 cd m^-2 to 30 150 cd m^-2, from 7.20 cd A^-1 (at 6.8 V) to 10.05 cd A^-1 (at 6.6 V), and from 1.73% to 2.44%, respectively. The ultrathin PFO layer not only reduces the exciton quenching at the interface between the hole-transport layer and emission layer, but also passivates the shallow-trap ensure increasing hole injection, as well as increases the coverage of perovskite film.

84% efficiency improvement in all-inorganic perovskite light-emitting diodes assisted by a phosphorescent material

A novel mixed perovskite emitter layer is applied to design all-inorganic cesium lead halide perovskite light-emitting diodes (PeLEDs) with high electroluminescence (EL) performance, by combining CsPbBr₃ with iridium(iii)bis[2-(4′,6′-difluorophenyl)pyridinato-N,C²′]-picolinate (FIrpic), where FIrpic is a phosphorescent material with very high internal quantum efficiency (IQE) approaching 100%. The CsPbBr₃:FIrpic PeLEDs show a maximum luminance of 5486 cd m⁻², and an external quantum efficiency of 0.47%, which are 1.84 and 1.76 times that of neat CsPbBr₃ PeLEDs, respectively. It is found that FIrpic molecules as an assistant dopant can efficiently transmit energy from the excitons of FIrpic to the excited state of the CsPbBr₃ emitter via a Förster energy transfer process, leading to enhanced EL efficiency in the CsPbBr₃:FIrpic PeLEDs.

Remarkable EL performance is achieved in CsPbBr₃:FIrpic perovskite light-emitting diodes assisted by a phosphorescent material.

Room temperature two-photon-pumped random lasers in FAPbBr3/polyethylene oxide (PEO) composite perovskite thin film

Solution-processed organic–inorganic halide lead perovskites have attracted increasing attention due to their great potential in low-cost, effective, and versatile light emission applications and large-scale portable optoelectronic devices. In this paper, formamidinium lead tribromide perovskite thin films composited with polyethylene oxide (PEO) were fabricated by a solution processing method. Great enhancement of photoluminescence was observed and more attractively, two-photon-pumped random lasing action could be achieved at room temperature when pumped by a nanosecond pulse laser with excitation wavelength centered at 1064 nm. Evident transition from spontaneous upconversion emission to random lasing action was investigated by monitoring the log–log light emission slope and peak width at half height. The lasing threshold is at around 1.1 mJ cm⁻², which is comparable to that of other two-photon upconversion random lasers. The efficient random lasing emission originates from the multiple random scattering provided by the micrometer-scale rugged morphology and polycrystalline grain boundaries. Compared with conventional lasers that normally serve as a coherent light source, the perovskite random lasers show promise in fabricating low-cost thin-film lasing devices for flexible and speckle-free imaging applications.

Solution-processed organic–inorganic halide lead perovskites have attracted increasing attention due to their great potential in low-cost, effective, and versatile light emission applications and large-scale portable optoelectronic devices.

Perovskite Quantum Dots and Their Application in Light-Emitting Diodes

Perovskite quantum dots (PQDs) attract significant interest in recent years because of their unique optical properties, such as tunable wavelength, narrow emission, and high photoluminescence quantum efficiency (PLQY). Recent studies report new types of formamidinium (FA) PbBr₃ PQDs, PQDs with organic-inorganic mixed cations, divalent cation doped colloidal CsPb_1-x M_x Br₃ PQDs (M = Sn²⁺ , Cd²⁺ , Zn²⁺ , Mn²⁺ ) featuring partial cation exchange, and heterovalent cation doped into PQDs (Bi³⁺ ). These PQD analogs open new possibilities for optoelectronic devices. For commercial applications in lighting and backlight displays, stability of PQDs requires further improvement to prevent their degradation by temperature, oxygen, moisture, and light. Oxygen and moisture-facilitated ion migration may easily etch unstable PQDs. Easy ion migration may result in crystal growth, which lowers PLQY of PQDs. Surface coating and treatment are important procedures for overcoming such factors. In this study, new types of PQDs and a strategy of improving their stabilities are introduced. Finally, this paper discusses future applications of PQDs in light-emitting diodes.

High Performance Metal Halide Perovskite Light-Emitting Diode: From Material Design to Device Optimization

Metal halide perovskites have drawn significant interest in the past decade. Superior optoelectronic properties, such as a narrow bandwidth, precise and facile tunable luminance over the entire visible spectrum, and high photoluminescence quantum yield of up to ≈100%, render metal halide perovskites suitable for next-generation high-definition displays and healthy lighting systems. The external quantum efficiency of perovskite light-emitting diodes (LEDs) increases from 0.1 to 11.7% in three years; however, the energy conversion efficiency and the long-term stability of perovskite LEDs are inadequate for practical application. Strategies to optimize the emitting layer and the device structure, with respect to material design, synthesis, surface passivation, and device optimization, are reviewed and highlighted. The long-term stability of perovskite LEDs is evaluated as well. Meanwhile, several challenges and prospects for future development of perovskite materials and LEDs are identified.

High Photoluminescence Quantum Yields in Organic Semiconductor-Perovskite Composite Thin Films

One of the obstacles towards efficient radiative recombination in hybrid perovskites is a low exciton binding energy, typically in the orders of tens of meV. It has been shown that the use of electron-donor additives can lead to a substantial reduction of the non-radiative recombination in perovskite films. Herein, the approach using small molecules with semiconducting properties, which are candidates to be implemented in future optoelectronic devices, is presented. In particular, highly luminescent perovskite-organic semiconductor composite thin films have been developed, which can be processed from solution in a simple coating step. By tuning the relative concentration of methylammonium lead bromide (MAPbBr₃ ) and 9,9spirobifluoren-2-yl-diphenyl-phosphine oxide (SPPO1), it is possible to achieve photoluminescent quantum yields (PLQYs) as high as 85 %. This is attributed to the dual functions of SPPO1 that limit the grain growth while passivating the perovskite surface. The electroluminescence of these materials was investigated by fabricating multilayer LEDs, where charge injection and transport was found to be severely hindered for the perovskite/SPPO1 material. This was alleviated by partially substituting SPPO1 with a hole-transporting material, 1,3-bis(N-carbazolyl)benzene (mCP), leading to bright electroluminescence. The potential of combining perovskite and organic semiconductors to prepare materials with improved properties opens new avenues for the preparation of simple lightemitting devices using perovskites as the emitter.

Nearly 100% Efficiency Enhancement of CH3NH3PbBr3 Perovskite Light-Emitting Diodes by Utilizing Plasmonic Au Nanoparticles

Organic-inorganic hybrid perovskites have drawn considerable attention due to their great potentials in lighting and displaying. Despite great progress being demonstrated in perovskites light-emitting diodes (PeLEDs), the commercialization of PeLEDs was still limited by their low efficiencies and poor device stabilities. Utilizing the metallic nanoparticles was a feasible way to further improve the efficiencies of PeLEDs. Herein, substantially enhanced electroluminescent performance of CH₃NH₃PbBr₃-based PeLEDs were first demonstrated by incorporating plasmonic gold nanoparticles (Au NPs) into the hole injection layer of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Compared to the reference device without Au NPs, 109% enhancement in maximum luminance and 97% enhancement in maximum EQE were achieved upon 9 vol % Au NPs doping. Such enhancements can be ascribed to the localized surface plasmon resonance between Au NPs and CH₃NH₃PbBr₃ excitons, as well as the enhanced electrical conductivity of modified PEDOT:PSS. Our studies indicated great potential of Au NPs in developing highly efficient PeLEDs.

Enhancing perovskite film fluorescence by simultaneous near- and far-field effects of gold nanoparticles

Gold nanoparticles are incorporated into PEDOT:PSS for enhanced perovskite fluorescence, which originates from simultaneous near- and far-field effects.

30-Fold efficiency enhancement achieved in the perovskite light-emitting diodes

30-Fold enhancement in electroluminescent performance in PeLEDs based on nearly 100% coverage perovskite film treated by only pumping away.