Large cation ethylammonium incorporated perovskite for efficient and spectra stable blue light-emitting diodes

Regulating Crystallization and Carrier Recombination of Quasi-2D Perovskite for Efficient Air-Processed Light-Emitting Diodes

Fabricating perovskite light-emitting diodes (PeLEDs) in ambient air is beneficial for reducing the production costs and promoting their further applications. However, the device performance is significantly restricted by the uncontrolled crystallization and unfavorable carrier recombination of the perovskite films when processing under an ambient environment. In this work, we report an effective strategy to tackle these issues by introducing a bifunctional molecule, formamidinium trifluoroacetate (FATFA). It is found that FATFA can accelerate the crystallization and reduce the defects in perovskites to improve carrier recombination. Accordingly, the air-processed green PeLEDs based on FATFA optimization exhibit a high external quantum efficiency exceeding 16%, with a maximum luminance approaching 33,000 cd m-2 and an operational half-lifetime of nearly 25 min at an initial brightness of ∼900 cd m-2, which represent the best-performed air-processed PeLEDs. This work provides a feasible way to realize cost-efficient PeLEDs and boost their practical applications in the future.

Promoting Phase Transition in Quasi-2D Perovskites For High-Performance Pure-Red LEDs

Layered quasi-two-dimensional (quasi-2D) halide perovskites have emerged as a promising platform for high-efficiency electroluminescence. Narrowing the multi-quantum well distribution and eliminating wide-bandgap 2D phases are crucial for achieving a flat energy landscape, minimizing energy loss, and ensuring high-color-purity emission. Here, it is demonstrated that solution-processed quasi-2D perovskite films with broad component distributions arise from an incomplete kinetic transition from low-n (n, quantum well thickness) to high-n phases. To address this, an acetate anion treatment strategy is proposed, which induces competitive coordination between the acetate anion, the bulky spacer cation, and the inorganic layer, thereby facilitating the insertion of octahedral precursor ions and promoting phase transition. This treatment results in quasi-2D films with enhanced color purity, efficient energy transfer, and high photoluminescence quantum yield. The fabricated perovskite light emitting diode (PeLED) exhibits an emission peak at 641 nm and a peak external quantum efficiency (EQE) of 25.3%, representing one of the most efficient pure-red PeLEDs. The strategy also showcases the versatility of quasi-2D films for different emission wavelengths.

Efficient and Super-Stable 990 Nm Light‑Emitting Diodes Based on Quantum Cutting Emission of Trivalent Ytterbium in Pure-Br Quasi‑2D Perovskites

Quasi 2D layered metal halide perovskites (2D-LMHPs) with natural quantum wells (QWs) structure have garnered significant attention due to their excellent optoelectronic properties. Doping rare earth (RE) ions with 4fn inner shell emission levels can largely expand their optical and optoelectronic properties and realize diverse applications, but has not been reported yet. Herein, an efficient Yb3+-doped PEA2Cs2Pb3Br10 quasi 2D-LMHPs is fabricated and directly identified the Yb3+ ions in the quasi 2D-LMHPs at the atomic scale using aberration electron microscopy. The interaction between different n phases and Yb3+ ions is elucidated using ultrafast transient absorption spectroscopy and luminescent dynamics, which demonstrated efficient, different time scales and multi-channel energy transfer processes. Finally, through phase distribution manipulation and surface passivation, the optimized film exhibits a photoluminescence quantum yield of 144%. This is the first demonstration of quantum cutting emission in pure Br-based perovskite material, suppressing defect states and ion migration. The efficient and stable near-infrared light-emitting diodes (NIR LED) is fabricated with a peak external quantum efficiency (EQE) of 8.8% at 990 nm and the record lifetime of 1274 min. This work provides fresh insight into the interaction between RE ions and quasi 2D-LMHPs and extend the function and application of quasi 2D-LMHPs materials.

Spacer Cation Engineering Enables Blue Quasi-2D Perovskites to Achieve Highly Efficient and Spectrally Stable Electroluminescence

The combination of organic spacer cations and mixed-halides to produce multiphase quasi-2D perovskites is a promising strategy for fabricating blue perovskite light-emitting diodes (PeLEDs). However, insufficient energy transfer, trap-assisted recombination and exciton-phonon coupling lead to significant non-radiative losses. Here, a co-spacer engineering strategy of binding guanidinium (GA+) and ortho-fluorophenylethylamium (oF-PEA+) through hydrogen bonds is proposed to prepare blue mixed-halide quasi-2D perovskite films with high photoluminescence quantum yields (PLQYs). GA+ with Lewis base characteristics reduces the trap states by defect passivation. Additionally, oF-PEA+ inhibits the rapid diffusion of GA+ by hydrogen bonding interactions, which mitigates the formation of undesirable low-dimensional phases and facilitates the growth of high-dimensional emissive phases with a more concentrated distribution, resulting in efficient energy transfer of excitons and weaker exciton-phonon coupling. These synergistic effects enable the blue perovskite films to achieve a PLQY as high as 91.5%. As a result, the fabricated blue PeLEDs show a remarkable external quantum efficiency of 21.1% at the stable emissionpeak of 489 nm with a narrow full width at half-maximum of 19 nm.

Blue Perovskite Light-Emitting Diodes Using Multifunctional Small Molecule Dopants

Unbalanced charge carrier injections and high densities of non-radiative recombination channels are still major obstacles to advancing high-efficiency blue perovskite light-emitting diodes (LEDs). Here, a deep-HOMO level p-type small molecule, (2-(3,6-dibromo-9H-carbazol-9-yl)ethyl)phosphonic acid, doped in blue perovskites for building a better-balanced injection and controlling over defects is demonstrated. During the perovskite film deposition process, most small molecules are extruded from the precursor solution to the bottom and top surfaces of the perovskite films. This unique distribution of molecules can construct a better-balanced carrier injection due to improved hole and retarded electron injection by its suitable energy-level structure, along with modulation of all defects in bulk and at the surface of doped films due to the formation of covalent bonds by its functional moiety. With this approach, a series of blue perovskite LEDs is designed with external quantum efficiencies (EQEs) of up to 24.03% (at a luminance of 113 cd m-2 and emission peak of 485 nm), 16.61% (at a luminance of 51 cd m-2 and emission peak of 476 nm) and 8.55% (at a luminance of 30 cd m-2 and emission perk of 467 nm), and encouraging operational stability.

Multiple defects renovation and phase reconstruction of reduced-dimensional perovskites via in situ chlorination for efficient deep-blue (454 nm) light-emitting diodes

Deep-blue perovskite light-emitting diodes (PeLEDs) based on reduced-dimensional perovskites (RDPs) still face a few challenges including severe trap-assisted nonradiative recombination, sluggish exciton transfer, and undesirable bathochromic shift of the electroluminescence spectra, impeding the realization of high-performance PeLEDs. Herein, an in situ chlorination (isCl) post-treatment strategy was employed to regulate phase reconstruction and renovate multiple defects of RDPs, leading to superior carrier cooling of 0.88 ps, extraordinary exciton binding energy of 122.53 meV, and higher photoluminescence quantum yield of 60.9% for RDP films with deep-blue emission at 450 nm. The phase regulation is accomplished via fluorine-derived hydrogen bonds that suppress the formation of small-n phases. Multiple defects, including halide vacancies (shallow-state defects) and lead-chloride antisite defects (deep-state defects), are renovated via C=O coordination and hydroxy-group-derived hydrogen bonds. Consequently, deep-blue PeLEDs with a record maximum external quantum efficiency of 6.17% and stable electroluminescence at 454 nm were demonstrated, representing the best-performing deep-blue PeLEDs.

Inhibiting ion migration in strontium-lead halide perovskite for pure-blue emission: a first-principle and experimental study

Bromide-chloride mixed perovskites have garnered significant attention as a direct and efficient material for achieving pure-blue emission. However, the complex problem of halide migration in mixed halide perovskites presents a significant obstacle to achieving stable electroluminescence (EL) spectra. Here, we investigate the mechanism of partially replacing the B-site Pb2+ with the non-toxic Sr2+ to achieve pure-blue emission based on first principles. The ion mobility activation energy of Sr2+ is 1.23 eV, which is an order of magnitude greater than that of halogens. Meanwhile, the incorporation of Sr2+ triples the activation energy for halogen migration. Furthermore, the halide defect formation energy increases from 4.75 eV to 5.62 eV, thereby reducing ion migration channels. Transient absorption spectroscopy demonstrates that suppressing the ion mobility pathway and enhancing ion mobility activation energy promotes the perovskite film to exhibit excellent spectral stability under laser pumping. Our work provides insights for the development of highly stable and eco-friendly perovskite devices.

The Perovskite Optoelectronic Devices - A Look at the Future

The perovskite materials are broadly incorporated into optoelectronic devices due to a number of advantages. Their rapid technological progress is related to the relatively simple fabrication process, low production cost and high efficiency. Significant improvement is made in the light emitting, detection performance and device design especially operating in the visible and near-infrared regions. This review presents the status and possible future development of the perovskite devices such as solar cells, photodetectors, and light-emitting diodes. The fundamental properties of perovskite materials related to their effective device applications are summarized. Since the development of the perovskite technology is mainly driven by the revolutionary evolution of the semiconductor perovskite solar cell as a robust candidate for next-generation solar energy harvesting, this topic is considered first. The device engineering of various perovskite photodetector structures, including perovskite quantum dot photodetectors, is then discussed in detail. Their performance is compared with the current commercial photodetectors available on the global market together with their challenges. Finally, the considerable progress in the fabrication of the perovskite light-emitting diodes with external quantum efficiency exceeding 20% is presented. The paper is completed in an attempt to determine the development of perovskite optoelectronic devices in the future.

Exciton Dynamics in Layered Halide Perovskite Light-Emitting Diodes

Layered halide perovskites have garnered significant interest due to their exceptional optoelectronic properties and great promises in light-emitting applications. Achieving high-performance perovskite light-emitting diodes (PeLEDs) requires a deep understanding of exciton dynamics in these materials. This review begins with a fundamental overview of the structural and photophysical properties of layered halide perovskites, then delves into the importance of dimensionality control and cascade energy transfer in quasi-2D PeLEDs. In the second half of the review, more complex exciton dynamics, such as multiexciton processes and triplet exciton dynamics, from the perspective of LEDs are explored. Through this comprehensive review, an in-depth understanding of the critical aspects of exciton dynamics in layered halide perovskites and their impacts on future research and technological advancements for layered halide PeLEDs is provided.

Impact of molecular configuration on the photoluminescence and electrical characteristics of poly-pyrrol-thiazol-imine polymers films

The optical, photoluminescence, and electrical properties of Poly(Z)-PTI and Poly(E)-PTI, two Poly-Pyrrol-Thiazol-Imine polymers with comparable chemical structures but distinct configurations, were examined. Using the dip-casting method, polymer films were deposited on ITO substrates. UV-VIS spectroscopy revealed that both polymers diverged between 500 and 800 nm, showing the impact of molecular arrangement, but showed similar absorption behavior for wavelengths shorter than 500 nm. For Poly(Z)-PTI, the direct optical energy gaps were 2.06 eV, while for Poly(E)-PTI, they were 1.78 eV. Poly(Z)-PTI displayed an emission peak at 610 nm (red) according to laser photoluminescence spectra, while Poly(E)-PTI peaked at 563 nm (green-yellow). The capacitance behavior was revealed by electrochemical impedance spectroscopy. Nyquist plots suggested an equivalent circuit model of Rs (CRct)(QR)(CR) for both polymers, and the relaxation times were 15.9 ns for Poly(Z)-PTI and 89.5 ns for Poly(E)-PTI. The Mott-Schottky analysis verified the n-type conductivity, revealing 2.18 × 1016 cm- 3 carrier densities for Poly(Z)-PTI and 1.78 × 1016 cm- 3 for Poly(E)-PTI. At lower frequencies, both polymers exhibited limited conductivity and large dielectric constants. Insights into the possible uses of Poly-Pyrrol-Thiazol-Imine polymers in electrical and optoelectronic devices are provided by this study, which emphasizes the influence of molecular configuration on these polymers' characteristics.

Phase Distribution Dictates Charge Transfer and Transport Dynamics in Layered Quasi-2D Perovskite

Strategic manipulation of spatiotemporal evolution of charge carriers is critical for optimizing performance of quasi-two-dimensional (2D) perovskite-based optoelectronic devices. Nonetheless, the inhomogeneous phase distribution and band alignment engender intricate energy landscapes, complicating internal charge and energy funneling processes. Herein, we integrate high spatiotemporal resolution transient absorption microscopy with multiple time-resolved spectroscopy and find that asynchronous electron and hole transfers rather than direct energy transfer govern the funneling mechanisms. Notably, the charge funneling pathways and transport behaviors can be modifiable by phase manipulation. The accumulation of small-n phases suppresses the electron funneling toward large-n phases and doubles the carrier diffusion rate from 0.085 to 0.20 cm2/s, yielding a 1.5-fold enhancement in diffusion length. Phase order engineering is further corroborated for facilitating charge separation. Our investigation underscores the prospects of manipulating the phase distribution to control internal charge funneling and transport, thereby substantiating the theoretical foundations for optimizing optoelectronic devices.

Chemical Reaction Modulated Low-Dimensional Phase Toward Highly Efficient Sky-Blue Perovskite Light-Emitting Diodes

Blue perovskite light-emitting diodes (PeLEDs) are crucial avenues for achieving full-color displays and lighting based on perovskite materials. However, the relatively low external quantum efficiency (EQE) has hindered their progression towards commercial applications. Quasi-two-dimensional (quasi-2D) perovskites stand out as promising candidates for blue PeLEDs, with optimized control over low-dimensional phases contributing to enhanced radiative properties of excitons. Herein, the impact of organic molecular dopants on the crystallization of various n-phase structures in quasi-2D perovskite films. The results reveal that the highly reactive bis(4-(trifluoromethyl)phenyl)phosphine oxide (BTF-PPO) molecule could effectively restrain the formation of organic spacer cation-ordered layered perovskite phases through chemical reactions, simultaneously passivate those uncoordinated Pb2+ defects. Consequently, the prepared PeLEDs exhibited a maximum EQE of 16.6 % (@ 490 nm). The finding provides a new route to design dopant molecules for phase modulation in quasi-2D PeLEDs.

Organic ammonium salt assisted crystallization and defect passivation of a quasi-two-dimensional pure blue perovskite at the buried interface

Quasi-two-dimensional (quasi-2D) perovskites exhibit excellent performance in light-emitting diodes (LEDs). However, the quality of perovskite films prepared via the solution method is significantly impacted by the enormous number of defects that unavoidably form at the grain boundaries and interfaces during the precursor to the crystal formation process. Here, we propose a strategy to assist perovskite crystallization and defect passivation at the buried interface through interfacial modification. The organic ammonium salt, ethylamine chloride (EACl), is added to the hole transport material and modifies the buried interface of the perovskite film. EACl introduces the nucleation sites for perovskite precursors, and promotes the crystallization process of the perovskite grains, contributing to the formation of high-quality perovskite films. At the same time, the presence of Lewis base (-NH2) groups in EACl and their lone electron pairs effectively inactivate unlocated Pb2+ ions at the buried interface, thereby reducing non-radiative recombination. In addition, chloride ions help to mitigate defects and to improve the morphology of perovskite films. Devices with this modification show a higher performance than control devices on all metrics. This work proposes a facile but efficient way for improving quasi-2D pure blue perovskite crystallization and growth.

Synergistic Steric Effect of Precursor And Antisolvent Enables Strongly Confined Perovskite Films with Efficient and Spectral Stable Blue Emission

Reducing the crystal size of perovskites to the strong quantum confinement regime is an effective way to realize blue luminescence for light-emitting applications. However, challenges remain in directly constraining the crystal growth during film preparation to achieve three-dimensional quantum confinement, and the widely used long-chain ligands may bring difficulties for charge transport and unfavorably affect the device performance. Herein, we report a novel strategy for fabricating strongly confined blue-emitting perovskite nanocrystalline films via synergistic steric effect modulation by precursors and antisolvents. We synthesize cesium pentafluoropropanoate (CsPFPA) as a new type of precursor agent, where the steric effect of the PFPA group can help constrain the growth of perovskite crystals and passivate the defects. Furthermore, different types of antisolvents with varied molecular sizes and steric hindrance are used to regulate the size of perovskite crystals and improve film quality. Consequently, highly emissive blue perovskite films are realized with the emission wavelength effectively tuned in the blue region by varying the concentration of CsPFPA as well as the type of antisolvents. Based on the strongly confined perovskite films, blue light-emitting diodes (LEDs) are constructed, showing good spectral tunability and stability in the electroluminescence. This work demonstrates a novel pathway for developing bright perovskite blue emitters for LEDs, which may potentially advance their future applications in display and lighting.

The Crystallization Regulation Effect of the Phenyl Ring of Passivators for Blue Perovskite Light-Emitting Diodes

Although metal halide perovskites (MHPs) have demonstrated remarkable external quantum efficiencies (EQEs) in red and green light-emitting diodes (LEDs), the blue ones confront efficiency and stability problems due to the high defect density in the perovskite films. Large amounts of defect passivation strategies are successfully developed to improve the device performance. Nevertheless, the influence of the molecular configuration of the passivators on the perovskite crystallization process has not been comprehensively investigated so far. Here, we investigate the effect of the phenyl ring on the perovskite crystallization dynamics and the passivation effect. The additive with a phenyl ring performs the π-π stacking ability with phenethylammonium (PEA+) molecules, resulting in a deteriorated crystallinity and a weakened passivation ability. Conversely, the additive without the phenyl ring is helpful to promote the participation of PEA+ molecules in the crystalline process, leading to a higher crystallinity and a stronger passivation effect. As a result, the EQE of the blue perovskite LED has increased from 4.72 to 11.06% by using the phenyl ring-free additive. Therefore, it is advisible to develop the conjugated nonplanar additives in the PEA+-assisted quasi-two-dimensional perovskites. This finding may enlighten the rational design of defect passivators for highly efficient perovskite LEDs.

Efficient deep-blue electroluminescence from Ce-based metal halide

Rare earth ions with d-f transitions (Ce3+, Eu2+) have emerged as promising candidates for electroluminescence applications due to their abundant emission spectra, high light conversion efficiency, and excellent stability. However, directly injecting charge into 4f orbitals remains a significant challenge, resulting in unsatisfied external quantum efficiency and high operating voltage in rare earth light-emitting diodes. Herein, we propose a scheme to solve the difficulty by utilizing the energy transfer process. X-ray photoelectron spectroscopy and transient absorption spectra suggest that the Cs3CeI6 luminescence process is primarily driven by the energy transfer from the I2-based self-trapped exciton to the Ce-based Frenkel exciton. Furthermore, energy transfer efficiency is largely improved by enhancing the spectra overlap between the self-trapped exciton emission and the Ce-based Frenkel exciton excitation. When implemented as an active layer in light-emitting diodes, they show the maximum brightness and external quantum efficiency of 1073 cd m-2 and 7.9%, respectively.

Efficient Quasi-2D Perovskite Based Blue Light-Emitting Diodes with Carbon Dots Modified Hole Transport Layer

Quasi-2D perovskites based blue light-emitting diodes (LEDs) suffer from its poor electroluminescence performance, mainly caused by the nonradiative recombination in in defect-rich low-n phases and the unbalanced hole-electron injection in the device. Here, we developed a highly efficient quasi-2D perovskite based sky-blue LEDs behaving recorded external quantum efficiency (EQE) of 21.07% by employing carbon dots (CDs) as additives in the hole transport layer (HTL). We ascribe the high EQE to the effective engineering of CDs: (1) The CDs at the interface of HTLs can suppress the formation of low-efficient n = 1 phase, resulting a high luminescence quantum yield and energy transfer efficiency of the mixed n-phase quasi-2D perovskites. (2) The CDs additives can reduce the conductivity of HTL, partially blocking the hole injection, and thus making more balanced hole-electron injection. The CDs-treated devices have excellent Spectral stability and enhanced operational stability and could be a new alternative additive in the perovskite optoelectronic devices.

Phase Engineering Reinforced Energy Transfer for High-Performance Blue Perovskite Light-Emitting Diodes

Layered metal-halide perovskites, a category of self-assembled quantum wells, are of paramount importance in emerging photonic sources, such as lasers and light-emitting diodes (LEDs). Despite high trap density in two-dimensional (2D) perovskites, efficient non-radiative energy funneling from wide- to narrow-bandgap components, sustained by the Förster resonance energy transfer (FRET) mechanism, contributes to efficient luminescence by light or electrical injection. Herein, it is demonstrated that bandgap extension of layered perovskites to the blue-emitting regime will cause sluggish and inefficient FRET, stemming from the tiny spectral overlap between different phases. Motivated by the importance of blue LEDs and inefficient energy transfer in materials with phase polydispersity, wide-bandgap quasi-2D perovskites with narrow phase distribution, improved crystallinity, and the pure crystal orientation perpendicular to the charge transport layer are developed. Based on this emitter, high-performance blue perovskite LEDs with improved electroluminescence (EL) external quantum efficiency (EQE) of 7.9% at 478 nm, a narrow full width at half-maximum (FWHM) of 22 nm and a more stable EL spectra are achieved. These results provide an important insight into spectrally stable and efficient blue emitters and EL devices based on perovskites.

Dielectric Regulation for Efficient Top-Emission Perovskite Light-Emitting Diodes with Suppressed Efficiency Roll-off

Perovskite light-emitting diodes (PeLEDs) have shown incalculable application potential in the fields of next-generation displays and light communication owing to the rapidly increased external quantum efficiencies (EQEs). However, most PeLEDs obtain a maximum EQE at small current density (J) region and suffer from severe efficiency roll-off in different extents. Herein, it is demonstrated that the dopant with large dipole moment like KBF4 facilitates the effective dielectric regulation of perovskite emissive layer. The increased dielectric constant lowers the exciton binding energy and suppresses the Auger recombination of the 2D/3D segregated perovskite structure, which improves the photoluminescence quantum yield remarkably at an excitation intensity up to 103 mW cm-2. Accordingly, the top-emission PeLED that delivers a high maximum EQE above 20% is fabricated and can retain EQE > 10% at an extremely high J of 708 mA cm-2. These results represent one of the most efficient top-emission PeLEDs with ultra-low efficiency roll-off, which provide a viable methodology for tuning the dielectric response of perovskite films for improved high radiance performance of perovskite electroluminescence devices.

Mixed cations tin-germanium perovskite: A promising approach for enhanced solar cell applications

Significant progress has been made over the years to improve the stability and efficiency of rapidly evolving tin-based perovskite solar cells (PSCs). One powerful approach to enhance the performance of these PSCs is through compositional engineering techniques, specifically by incorporating a mixed cation system at the A-site and B-site structure of the tin perovskite. These approaches will pave the way for unlocking the full potential of tin-based PSCs. Therefore, in this study, a theoretical investigation of mixed A-cations (FA, MA, EA, Cs) with a tin-germanium-based PSC was presented. The crystal structure distortion and optoelectronic properties were estimated. SCAPS 1-D simulations were employed to predict the photovoltaic performance of the optimized tin-germanium material using different electron transport layers (ETLs), hole transport layers (HTLs), active layer thicknesses, and cell temperatures. Our findings reveal that EA0.5Cs0.5Sn0.5Ge0.5I3 has a nearly cubic structure (t = 0.99) and a theoretical bandgap within the maximum Shockley-Queisser limit (1.34 eV). The overall cell performance is also improved by optimizing the perovskite layer thickness to 1200 nm, and it exhibits remarkable stability as the temperature increases. The short-circuit current density (Jsc) remains consistent around 33.7 mA/cm2, and the open-circuit voltage (Voc) is well-maintained above 1 V by utilizing FTO as the conductive layer, ZnO as the ETL, Cu2O as the HTL, and Au as the metal back contact. This configuration also achieves a high fill factor ranging from 87 % to 88 %, with the highest power conversion efficiency (PCE) of 31.49 % at 293 K. This research contributes to the advancement of tin-germanium perovskite materials for a wide range of optoelectronic applications.

Energy Transfer-Dominated Quasi-2D Blue Perovskite Light-Emitting Diodes

The bromide-chloride mixed quasi-two-dimensional (2D) perovskite, with a natural quantum well structure and tunable exciton binding energy, has gained significant attention for high-performance blue perovskite light-emitting diodes (PeLEDs). However, the relative importance of having a low trap state density or efficient exciton transfer for high-efficiency electroluminescence (EL) performance remains elusive. Here, two molecules with the benzoic acid group, sodium 4-fluorobenzoate (SFB) and 3,5-dibromobenzoic acid (DBA), are used to modulate the phase distribution and trap state to explore the effect between energy transfer and defect passivation. As a result, when the n = 1 phase is inhibited in both films, the DBA@SFB-modified perovskite films achieve a higher photoluminescence quantum yield (PLQY) than the SFB-modified perovskite films due to effective defect passivation. However, DBA@SFB-modified PeLEDs exhibit lower external quantum efficiency (EQE) compared to SFB-modified PeLEDs due to the poor exciton transfer between the low-dimensional phase. This demonstrates that passivation strategies may enhance photoluminescence through reducing nonradiative recombination, but the effect of phase distribution is pivotal for EL performance by efficient energy transfer in quasi-2D perovskites. Femtosecond time-resolved transient absorption measurements confirm the fastest carrier dynamics in SFB-modified perovskite films, further corroborating the above result. This work provides useful information about phase modulation and defect passivation for high-efficiency blue quasi-2D PeLEDs.

Photocurrent Enhancement by Copper Incorporation in Chemical-Solution-Synthesized Inorganic Lead Perovskite Thin Films

Perovskite thin films are at the forefront of highly promising photovoltaic technologies due to their remarkable optoelectronic properties. Herein, we explore a low-cost, reproducible, and industry-scalable methodology to synthesize an all-inorganic CsPbI1.5Br1.5 perovskite thin film with additional incorporation of copper and chloride ions into the lattice structure. The synthesis process involves chemical bath deposition of PbS, followed by a gas-solid iodination reaction to yield PbI2. Subsequently, dip-coating incorporates Cs+, Cu2+, Br-, and Cl- ions into PbI2, and annealing at 270 °C produces perovskite thin films. The results show a large coverage area and a uniform thickness of each perovskite thin film. Comprehensive characterization, including X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and photoluminescence, provides the structural, chemical, and optical properties of the synthesized thin films. To evaluate the practical implications of our methodology, we fabricated photodetectors employing CsPbI1.5Br1.5 and (Cs0.95:Cu0.01)PbI1.5Br1.3Cl0.1 perovskite films. A comparative analysis unequivocally demonstrates a significant increase in photodetector performance when utilizing (Cs0.95:Cu0.01)PbI1.5Br1.3Cl0.1 perovskite films. While our findings quantitatively assess the tangible enhancement in photocurrent, we acknowledge the potential for improvement in device fabrication to enhance the overall performance. This study not only affirms the successful low-cost synthesis of perovskite thin films but also emphasizes the pivotal role of Cu2+ and Cl- ions in enhancing the performance of perovskite-based optoelectronic devices.

Stereo-Hindrance Engineering of A Cation toward <110>-Oriented 2D Perovskite with Minimized Tilting and High-Performance X-Ray Detection

2D <100>-oriented Dion-Jacobson or Ruddlesden-Popper perovskites are widely recognized as promising candidates for optoelectronic applications. However, the large interlayer spacing significantly hinders the carrier transport. <110>-oriented 2D perovskites naturally exhibit reduced interlayer spacings, but the tilting of metal halide octahedra is typically serious and leads to poor charge transport. Herein, a <110>-oriented 2D perovskite EPZPbBr4 (EPZ = 1-ethylpiperazine) with minimized tilting is designed through A-site stereo-hindrance engineering. The piperazine functional group enters the space enclosed by the three [PbBr6 ]4- octahedra, pushing Pb─Br─Pb closer to a straight line (maximum Pb─Br─Pb angle ≈180°), suppressing the tilting as well as electron-phonon coupling. Meanwhile, the ethyl group is located between layers and contributes an extremely reduced effective interlayer distance (2.22 Å), further facilitating the carrier transport. As a result, EPZPbBr4 simultaneously demonstrates high µτ product (1.8 × 10-3 cm2 V-1 ) and large resistivity (2.17 × 1010 Ω cm). The assembled X-ray detector achieves low dark current of 1.02 × 10-10 A cm-2 and high sensitivity of 1240 µC Gy-1 cm-2 under the same bias voltage. The realized specific detectivity (ratio of sensitivity to noise current density, 1.23 × 108 µC Gy-1 cm-1 A-1/2 ) is the highest among all reported perovskite X-ray detectors.

In Situ Hydrolysis of Phosphate Enabling Sky-Blue Perovskite Light-Emitting Diode with EQE Approaching 16.32

The performance of blue perovskite light-emitting diodes (PeLEDs) lags behind the green and red counterparts owing to high trap density and undesirable red shift of the electroluminescence spectrum under operation conditions. Organic molecular additives were employed as passivators in previous reports. However, most commonly have limited functions, making it challenging to effectively address both efficiency and stability issues simultaneously. Herein, we reported an innovatively dynamic in situ hydrolysis strategy to modulate quasi-2D sky-blue perovskites by the multifunctional passivator phenyl dichlorophosphate that not only passivated the defects but also underwent in situ hydrolysis reaction to stabilize the emission. Moreover, hydrolysis products were beneficial for low-dimensional phase manipulation. Eventually, we obtained high-performance sky-blue PeLEDs with a maximum external quantum efficiency (EQE) of 16.32% and an exceptional luminance of 5740 cd m-2. More importantly, the emission peak of devices located at 485 nm remained stable under different biases. Our work signified the significant advancement toward realizing future applications of PeLEDs.

Defects in lead halide perovskite light-emitting diodes under electric field: from behavior to passivation strategies

Lead halide perovskites (LHPs) are emerging semiconductor materials for light-emitting diodes (LEDs) owing to their unique structure and superior optoelectronic properties. However, defects that initiate degradation of LHPs through external stimuli and prompt internal ion migration at the interfaces remain a significant challenge. The electric field (EF), which is a fundamental driving force in LED operation, complicates the role of these defects in the physical and chemical properties of LHPs. A deeper understanding of EF-induced defect behavior is crucial for optimizing the LED performance. In this review, the origins and characterization of defects are explored, indicating the influence of EF-induced defect dynamics on LED performance and stability. A comprehensive overview of recent defect passivation approaches for LHP bulk films and nanocrystals (NCs) is also provided. Given the ubiquity of EF, a summary of the EF-induced defect behavior can enhance the performance of perovskite LEDs and related optoelectronic devices.

Bright Blue Emission Lead-Free Halides with Narrow Bandwidth Enabled by Oversaturated Europium Doping

Eu2+-based lead-free metal halide nanocrystals (LFMH NCs), including CsEuCl3 NCs and CsX:Eu2+ NCs (X = Cl or Br), exhibit highly efficient narrow-band blue photoluminescence, making them competitive candidates for next-generation lighting and displays. However, the growing mechanism of the aforementioned NCs lacks in-depth study, which hinders the development of Eu2+-based nanomaterials. Herein, we demonstrate the colloidal synthesis of CsBr:Eu2+ NCs based on an air-stable europium source. The NCs show deep blue photoluminescence centered at 444 nm, with a maximum photoluminescence quantum yield (PLQY) reaching 53.4% and a fwhm of 30 nm. We further reveal the mechanism that determines CsBr host growth and Eu2+ doping in CsBr:Eu2+ nanocrystals, especially dopant trapping and self-purification, that determine the PLQY level. Pure white, warm white, and cold white LEDs are fabricated based on CsBr:Eu2+ NCs, red and green phosphors, and their performance suits the needs of high-quality lighting.

Development of Quasi-Two-Dimensional Perovskites and Their Application in Light-Emitting Diodes

Quasi-two-dimensional (quasi-2D) perovskites have attracted much attention due to their outstanding properties, such as inherent quantum-well structure, strong dielectric and quantum confinement, large exciton binding energy, and high photoluminescence quantum yield. By virtue of these superior merits, quasi-2D perovskites have shown great potential for next-generation light-emitting diodes (LEDs). Herein, this review presents an overview of the basic properties of quasi-2D perovskites and their photoluminescence modulations by large organic cation engineering, monovalent cation engineering, halogen engineering, defect passivation engineering, and dimensionality engineering. Furthermore, the strategies of charge-transport layer optimization, interfacial engineering, light-outcoupling efficiency improvement, and operating stability improvement are summarized for fabricating high-performance quasi-2D perovskite LEDs (PeLEDs). Finally, the challenges and outlook for the future development of quasi-2D PeLEDs are unambiguously proposed.

Postdeposition Halide Exchange for Achieving Deep-Blue Perovskite Light-Emitting Diodes: The Role of the Organic Cations in the Chloride Source

Postdeposition halide exchange has been a popular strategy for tuning the emission wavelength of metal halide perovskites and is particularly attractive in achieving deep-blue perovskite light-emitting diodes (PeLEDs), where the quality of the emissive layer is largely limited by the low solubility of chlorides in perovskite precursor solution. In this work, the halide exchange strategy is examined for deep-blue PeLEDs, with a focus on understanding the role of the organic cations of the halide salt (i.e., the chloride source for ion exchange) in modifying the properties of the perovskite films and consequently the PeLED performances. By comparatively investigating the treatment effects of two model systems, namely phenethylammonium chloride and 2,2-diphenylethylammonium chloride (DPEACl), it is found that although the two chlorides produce highly similar photoluminescence properties of the perovskite films, they create different landscapes for current flow in the PeLEDs. In particular, the bulky branch-structured DPEA cations exhibit minimal disturbance to the perovskite grains while providing highly effective inter-grain void filling and thus leakage current blocking, leading to 3D perovskite-based PeLEDs with a record high peak external quantum efficiency of 6.4% at 462 nm. The study highlights the importance of organic cation selection in the halide exchange processes for PeLEDs.

Unusual Pressure-Induced Self-Trapped Exciton to Free Exciton Transfer in Chiral 2D Lead Bromide Perovskites

The phenomenon of pressure-induced emission alterations related to complex excitonic dynamics in 2D lead halide perovskites (LHPs) has gained considerable attention for understanding their structure-property relationship and obtaining inaccessible luminescence under ambient conditions. However, the well-known pressure-induced emissions are limited to the formation of self-trapped excitons (STEs) due to the structural distortion under compression, which goes against the advantage of the highly pure emission of LHPs. Here, the pressure-induced detrapping from STEs to free excitons (FEs) accompanied by the dramatic transition from broadband orangish emission to narrow blue emission has been achieved in chiral 2D LHPs and R- and S-[4MeOPEA]2PbBr4, (4MeOPEA = 4-methoxy-α-methylbenzylammonium). The combined experimental and calculated results reveal that the distortion level of PbBr6 octahedra of R- and S-[4MeOPEA]2PbBr4 exhibits an unusually significant reduction as the applied pressure increases, which leads to decreased electron-phonon coupling and self-trapped energy barrier and consequently enables the detrapping of STEs to FEs. This work illustrates the dramatic exciton transfer in 2D LHPs and highlights the potential for realizing highly efficient and pure light emissions by manipulating the structural distortion via strain engineering.

Homogenized NiOx nanoparticles for improved hole transport in inverted perovskite solar cells

The power conversion efficiency (PCE) of inverted perovskite solar cells (PSCs) is still lagging behind that of conventional PSCs, in part because of inefficient carrier transport and poor morphology of hole transport layers (HTLs). We optimized self-assembly of [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) onto nickel oxide (NiOx) nanoparticles as an HTL through treatment with hydrogen peroxide, which created a more uniform dispersion of nanoparticles with high conductivity attributed to the formation of Ni3+ as well as surface hydroxyl groups for bonding. A 25.2% certified PCE for a mask size of 0.074 square centimeters was obtained. This device maintained 85.4% of the initial PCE after 1000 hours of stabilized power output operation under 1 sun light irradiation at about 50°C and 85.1% of the initial PCE after 500 hours of accelerated aging at 85°C. We obtained a PCE of 21.0% for a minimodule with an aperture area of 14.65 square centimeters.

Recent Advances and Opportunities of Eco-Friendly Ternary Copper Halides: A New Superstar in Optoelectronic Applications

Recently, the newly-emerging lead-free metal-halide materials with less toxicity and superior optoelectronic properties have received wide attention as the safer and potentially more robust alternatives to lead-based perovskite counterparts. Among them, ternary copper halides (TCHs) have become a vital group due to their unique features, including abundant structural diversity, ease of synthesis, unprecedented optoelectronic properties, high abundance, and low cost. Although the recent efforts in this field have made certain progresses, some scientific and technological issues still remain unresolved. Herein, a comprehensive and up-to-date overview of recent progress on the fundamental characteristics of TCH materials and their versatile applications is presented, which contains topics such as: i) crystal and electronic structure features and synthesis strategies; ii) mechanisms of self-trapped excitons, luminescence regulation, and environmental stability; and iii) their burgeoning optoelectronic devices of phosphor-converted white light-emitting diodes (WLEDs), electroluminescent LEDs, anti-counterfeiting, X-ray scintillators, photodetectors, sensors, and memristors. Finally, the current challenges together with future perspectives on the development of TCH materials and applications are also critically described, which is considered to be critical for accelerating the commercialization of these rapidly evolving technologies.

Strengthened Surface Modification for High-Performance Inorganic Perovskite Solar Cells with 21.3% Efficiency

Metal halide inorganic perovskites show excellent thermal stability compared to organic-inorganic perovskites. However, the performance of inorganic perovskite solar cells (PSCs) is far from theoretical values, together with unsatisfactory stability, mainly due to the poor interfacial properties. In this work, a facial but effective method is reported to realize high-performance inorganic PSCs by post-modifying the perovskite surface with 2-thiophene ethylamine (TEA). It is found that amine group from TEA can favorably interact with the undercoordinated Pb2+ via Lewis acid-based coordination, while thiophene ring with electron-rich sulfur assists such interaction by functioning as an electron donor. The synergetic interaction allows TEA to passivate perovskite film defects more efficiently, as compared to phenethylamine (PEA) with less electron-donating ability. Moreover, perovskite valence band is slightly upward shift to match with hole transport material and facilitate hole transfer. These combinations result in a reduced non-radiative charge recombination and improved charge carrier lifetime. Consequently, PSCs with TEA modification shows a drastic improvement of VOC by 54 mV, yielding a champion PCE of 21.3%, much higher than the control PSCs (19.3%), along with improved ambient stability. This work demonstrates that surface modifier with an electron-rich moiety is critical for achieving efficient and stable inorganic PSCs.

Microwave-assisted of new derivatives of polyimine conjugated polymer based on Schiff base: synthesis, characterization, and photo-physical properties as a photoluminescent materials

The condensation of pyrrole-2,5-dicarbaldehyde (1) with 5-(2-amino-4-phenylthiazol-5-yl)-4-phenylthiazol-2-amine (2) and/or 5-(4-Amino-phenyl)-4-phenylthiazol-2-amine (3) gave new poly(Z)-N-((5-(iminomethyl)-1H-pyrrol-2-yl)methylene)-5-(2-((E)-(5-(iminomethyl)-I-pyrrol-2-yl)methyleneamino)-4-phenylthiazol-5-yl)-4-phenylthiaol-2-amine (P1) and/or poly(E)-N-((5-(iminomethyl)-1H-pyrrol-2-yl)methylene)-5-(4-((E)-(5-(iminomethyl)-1H-pyrrol-2-yl)methyleneamino)phenyl)-4-phenylthiaol-2-amine (P2) as a novel conjugated polymer by microwave irradiation and traditional heating.. It is evident that the microwave irradiation technique quickly raised the molecular weight of polyimines. In addition to quantifying the molecular weight of the resultant polyimines. All the polyimines were characterized using FTIR, XRD, H1NMR, TGA, and DSC. The optical characteristics of polyimine derivatives were investigated using a UV-Vis spectrophotometer. The absorption spectra showed a main absorption band around 372 nm for polyimine (P1) and 381 nm for polyimine (P2). The optical energy was calculated and found to be 2.49 and 2.68 eV. The photoluminescence of the polyimine derivatives was measured and analyzed by spectrofluorometer and Laser photoluminescence experiment and the emission color was studied using CIE graphs. The fluorescence spectra showed an emission peak at 548 nm for polyimine (P1) with yellow green color in CIE graph, while for polyimine (P2) the emission band was located at 440.5 nm with blue color in CIE graph. Photoluminescence quantum yield PLQY was measured for the polyimine P1 and P2 in both liquid and Solid states and indicated the AIE behavior of the polyimines. TD-DFT simulations were applied to the polyimine derivatives where the structures were geometrically optimized and the spectroscopic characterizations were evaluated.

Potential and perspectives of halide perovskites in light emitting devices

Light emitting diodes (LEDs) have become part of numerous electrical and electronic systems such as lighting, displays, status indicator lamps and wearable electronics. Owing to their excellent optoelectronic properties and deposition via simple solution process, metal halide perovskites possess unique potential for developing halide perovskite-based LEDs (PeLEDs) with superior photoluminescence efficiencies leading to external quantum efficiencies beyond 20% for PeLEDS. However, the limited durability, high operative voltages, and challenges of scale-up are persisting barriers in achieving required technology readiness levels. To build up the existing knowledge and raise the device performance this review provides a state-of-the-art study on the properties, film and device fabrication, efficiency, and stability of PeLEDs. In terms of commercialization, PeLEDs need to overcome materials and device challenges including stability, ion migration, phase segregation, and joule heating, which are discussed in this review. We hope, discussions about the strategies to overcome the stability issues and enhancement the materials intrinsic properties towards development more stable and efficient optoelectronic devices can pave the way for scalability and cost-effective production of PeLEDs.

Charge injection engineering at organic/inorganic heterointerfaces for high-efficiency and fast-response perovskite light-emitting diodes

The development of advanced perovskite emitters has considerably improved the performance of perovskite light-emitting diodes (LEDs). However, the further development of perovskite LEDs requires ideal device electrical properties, which strongly depend on its interfaces. In perovskite LEDs with conventional p-i-n structures, hole injection is generally less efficient than electron injection, causing charge imbalance. Furthermore, the popular hole injection structure of NiOx/poly(9-vinylcarbazole) suffers from several issues, such as weak interfacial adhesion, high interfacial trap density and mismatched energy levels. In this work, we insert a self-assembled monolayer of [2-(9H-carbazol-9-yl)ethyl]phosphonic acid between the NiOx and poly(9-vinylcarbazole) layers to overcome these challenges at the organic/inorganic heterointerfaces by establishing a robust interface, passivating interfacial trap states and aligning the energy levels. We successfully demonstrate blue (emission at 493 nm) and green (emission at 515 nm) devices with external quantum efficiencies of 14.5% and 26.0%, respectively. More importantly, the self-assembled monolayer also gives rise to devices with much faster response speeds by reducing interfacial capacitance and resistance. Our results pave the way for developing more efficient and brighter perovskite LEDs with quick response, widening their potential application scope.

All-Thermally Evaporated Blue Perovskite Light-Emitting Diodes for Active Matrix Displays

With the rapid progress of perovskite light-emitting diodes (PeLEDs), the large-scale fabrication of active matrix PeLED displays (AM-PeLEDs) is gaining increasing attention. However, the integration of high-resolution PeLED arrays with thin-film transistor backplanes remains a significant challenge for conventional spin-coating techniques. Here, the demonstration of large-area, blue-emitting AM-PeLEDs are demonstrated using a vacuum deposition technique, which is regarded as the most effective route for organic light-emitting diode displays. By the introduction of an in situ passivation strategy, the defects-related nonradiative recombination is largely suppressed, which leads to an improved photoluminescence quantum yield of vapor-deposited blue-emitting perovskites. The as-prepared blue PeLEDs exhibit a peak external quantum efficiency of 2.47% with pure-blue emission at 475 nm, which represents state-of-the-art performance for vapor-deposited pure-blue PeLEDs. Benefiting from the excellent uniformity and compatibility of thermal evaporation, the 6.67-inch blue-emitting AM-PeLED display with a high resolution of 394 pixels per inch is successfully demonstrated. The demonstration of blue-emitting AM-PeLED display represents a crucial step toward full-color perovskite display technology.

Luminescence and Degeneration Mechanism of Perovskite Light-Emitting Diodes and Strategies for Improving Device Performance

Perovskite light-emitting diodes (PeLEDs) can be a promising technology for next-generation display and lighting applications due to their excellent optoelectronic properties. However, a systematical overview of luminescence and degradation mechanism of perovskite materials and PeLEDs is lacking. Therefore, it is crucial to fully understand these mechanisms and further improve device performances. In this work, the fundamental photophysical processes of perovskite materials, electroluminescence mechanism of PeLEDs including carrier kinetics and efficiency roll-off as well as device degradation mechanism are discussed in detail. In addition, the strategies to improve device performances are summarized, including optimization of photoluminescence quantum yield, charge injection and recombination, and light outcoupling efficiency. It is hoped that this work can provide guidance for future development of PeLEDs and ultimately realize industrial applications.

A Multifunctional Additive Strategy Enables Efficient Pure-Blue Perovskite Light-Emitting Diodes

Lead halide perovskites have shown exceptional performance in light-emitting devices (PeLEDs), particularly in producing significant electroluminescence in sky-blue to near-infrared wavelengths. However, PeLEDs emitting pure-blue light at 465-475 nm are still not satisfactory. Herein, efficient and stable pure-blue PeLEDs are reported by controlling phase distribution, passivation of defects, as well as surface modifications using multifunctional phenylethylammonium trifluoroacetate (PEATFA) in reduced-dimensional p-F-PEA2 Csn-1 Pbn (Br0.55 Cl0.45 )3n+1 polycrystalline perovskite films. Compared with 4-fluorophenylethylammonium (p-F-PEA+ ) in the pristine films, phenylethylammonium (PEA+ ) has lower adsorption energy while interacting with perovskites, resulting in large-n low-dimensional perovskites, which can greatly facilitate charge transport within the low-dimensional perovskite films. The interaction between the CO group in trifluoroacetate (TFA- ) and perovskites significantly reduces defects in the perovskite films. Additionally, the electron-giving CF3 group in TFA- uplifts surface potential in the films, resulting in smooth electronic injection in devices. The multifunctional additive strategy leads to elevated radiative recombination and efficient carrier transport in the films and devices. As a result, the devices exhibit a maximum external quantum efficiency (EQE) of 11.87% at 468 nm with stable spectral output, the highest reported to date for pure-blue PeLEDs. Thus, this study extends the way for high-efficiency pure-blue LED with perovskite polycrystal films.

Manipulation of Charge Dynamics for Efficient and Bright Blue Perovskite Light-Emitting Diodes with Chiral Ligands

Perovskite light-emitting diodes (PeLEDs) emerge as a promising class of optoelectronic devices for next-generation displays and lighting technology. However, the performance of blue PeLEDs lags far behind that of their green and red counterparts, including the unachieved trade-off between high efficiency and high luminance, severe efficiency roll-off, and unsatisfactory power efficiency. Here, a multi-functional chiral ligand of L-phenylalanine methyl ester hydrochloride is strategically introduced into quasi-2D perovskites, which can effectively passivate defects, modulate the phase distribution, improve photoluminescence quantum yield, guarantee high-quality film morphology, and enhance charge transport. Furthermore, ladder-like hole transport layers are established, boosting charge injection and balance. The resultant sky-blue PeLEDs (the photoluminescence peak is 493 nm and the electroluminescence peak is 497 nm) exhibit an external quantum efficiency of 12.43% at 1000 cd m-2 and a record power efficiency of 18.42 lm W-1 , rendering that the performance is among the best blue PeLEDs.

Impact of Bychkov-Rashba Spin Splitting on Dual Emissions for Lead Halide Perovskite Nanowires

Bychkov-Rashba spin-orbit coupling (SOC) is decisive for photoinduced photoluminescence (PL) in terms of double emissions. It turns out to be remarkable for one-dimensional lead halide perovskite nanowires (PeNWs). This is primarily due to large surface to volume ratios and structural symmetry breaking fields in the reduced dimension. Systematic studies of the effect of Rashba SOC on PL and its discrimination with the self-trapped exciton in wide temperature and illumination intensity ranges are considerably important and, heretofore, have not been performed. Here, highly crystalline methylammonium lead triiodine (MAPbI3) PeNWs are demonstrated to be able to produce remarkable dual emissions at low temperatures. With extensive analyses by a photoelectrical device-based spin-photogalvanic effect and magnetophotoluminescence, the Rashba effect is proven to be the only factor that governs the dual emissions. We believe a complete understanding of the PL character of PeNWs is beneficial for the development of novel perovskite nanophotonic devices.

Advances in the Application of Perovskite Materials

Nowadays, the soar of photovoltaic performance of perovskite solar cells has set off a fever in the study of metal halide perovskite materials. The excellent optoelectronic properties and defect tolerance feature allow metal halide perovskite to be employed in a wide variety of applications. This article provides a holistic review over the current progress and future prospects of metal halide perovskite materials in representative promising applications, including traditional optoelectronic devices (solar cells, light-emitting diodes, photodetectors, lasers), and cutting-edge technologies in terms of neuromorphic devices (artificial synapses and memristors) and pressure-induced emission. This review highlights the fundamentals, the current progress and the remaining challenges for each application, aiming to provide a comprehensive overview of the development status and a navigation of future research for metal halide perovskite materials and devices.

Trifunctional Trichloroacetic Acid Incorporated Mixed-Halide Perovskites for Spectrally Stable Blue Light-Emitting Diodes

Metal halide perovskites have won great recognition in light-emitting diodes (LEDs). Nevertheless, the development of blue perovskite LEDs is facing a bottleneck in improving the device performance. Although mixed chloride/bromide perovskites can achieve pure-blue emission straightforwardly, higher chloride content will induce the challenges of low photoluminescence quantum yield and poor spectra stability resulting from the chloride vacancy defects and resultant halide ion migration under an electric field. In this work, we introduce a reliable trifunctional additive trichloroacetic acid into mixed-halide perovskites, which can provide additional chloride to fill halide vacancies, passivate the uncoordinated Pb²⁺ ion defects, and promote the crystallization effectively. Owning to the utilization of trichloroacetic acid, the ultimate pure-blue perovskite LED obtains stable electroluminescent spectra at 477 nm under various bias and demonstrates a 5-fold external quantum efficiency improvement (up to 6.6%).

Two-Dimensional Cs2 AgInx Bi1- x Cl6 Alloyed Double Perovskite Nanoplatelets for Solution-Processed Light-Emitting Diodes

Lead-free double perovskites have emerged as a promising class of materials with potential to be integrated into a wide range of optical and optoelectronic applications. Herein, the first synthesis of 2D Cs₂ AgIn_x Bi_{1- x} Cl₆ (0 ≤ x ≤ 1) alloyed double perovskite nanoplatelets (NPLs) with well controlled morphology and composition is demonstrated. The obtained NPLs show unique optical properties with the highest photoluminescence quantum yield of 40.1%. Both temperature dependent spectroscopic studies and density functional theory calculation results reveal that the morphological dimension reduction and In-Bi alloying effect together boost the radiative pathway of the self-trapped excitons of the alloyed double perovskite NPLs. Moreover, the NPLs exhibit good stability under ambient conditions and against polar solvents, which is ideal for all solution-processing of the materials in low-cost device manufacturing. The first solution-processed light-emitting diodes is demonstrated using the Cs₂ AgIn_0.9 Bi_0.1 Cl₆ alloyed double perovskite NPLs as the sole emitting component, showing luminance maximum of 58 cd m^-2 and peak current efficiency of 0.013 cd A^-1 . This study sheds light on morphological control and composition-property relationships of double perovskite nanocrystals, paving the way toward ultimate utilizations of lead-free perovskite materials in diverse sets of real-life applications.

Color-stable blue light-emitting diodes with defect management by sulfonate

Utilizing bromine-based quasi-two-dimensional (quasi-2D) perovskite is a feasible strategy to achieve efficient and stable blue perovskite light-emitting diodes (PeLEDs). However, dimension discretization is prone to emerge due to the irregular phase distribution and massive defects in the perovskite system. Here, we introduce alkali-salt to modulate the phase distribution for reducing the n = 1 phase and propose a novel Lewis base to serve as a passivating agent to decrease defects. This revealed that the external quantum efficiency (EQE) dramatically improves due to the suppression of severe non-radiative recombination losses. Consequently, efficient blue PeLEDs were obtained with a peak EQE of 3.82% located at 487 nm.

Tuning the energy transfer in Ruddlesden-Popper perovskites phases through isopropylammonium addition - towards efficient blue emitters

Here we demonstrate blue LEDs with a peak wavelength of 481 nm, with outstanding colour purity of up to 88% (CIE coordinates (0.1092, 0.1738)), an external quantum yield of 5.2% and a luminance of 8260 cd m^-2. These devices are based on quasi-2D PEA₂(Cs_0.75MA_0.25)Pb₂Br₇, which is cast from solutions containing isopropylammonium (iPAm). iPAm as additive assist in supressing the formation of bulk-like phases, as pointed out by both photophysical and structural characterization. Additionally, the study of the excitation dynamics demonstrates a hindering of the energy transfer to domains of lower energy that generally undermines the performance and emission characteristics of blue-emitting LEDs based on quasi-2D perovskites. The achieved narrow distribution of quantum well sizes and the hindered energy transfer result in a thin film photoluminescence quantum yield exceeding 60%. Our work demonstrates the great potential to tailor the composition and the structure of thin films based on Ruddlesden-Popper phases to boost performance of optoelectronic devices - specifically blue perovskite LEDs.

Multidentate Zwitterionic Ligand-Assisted Formation of Pure Bromide-Based Perovskite Nanosheets and Their Application in Blue Light-Emitting Diodes

Perovskite light-emitting diodes (PeLEDs) have demonstrated rapid development during the past decade, whereas the inferior device performance of blue ones impedes the application in full-color display and lighting. Low-dimensional perovskites turn out to be the most promising blue-emitters owing to their superior stability. In this work, a multidentate zwitterionic l-arginine is proposed to achieve blue emission from pure bromide-based perovskites by in situ-forming low-dimensional nanosheets. First, l-arginine can promote the formation of perovskite nanosheets due to the strong interaction between the peripheral guanidinium cations and [PbBr₆]^4- octahedral layers, enabling a significant blue-shift. Second, the carboxyl group within l-arginine can passivate uncoordinated Pb²⁺ ions, improving the device performance. Finally, a blue PeLED is successfully constructed on the basis of the l-arginine-modulated perovskite film, demonstrating a peak luminance of 2152 cd/m², an external quantum efficiency of 5.4%, and operation lifetime of 13.81 min. Further, the enlightenment from this work is hopefully to be applied in rationally designing spacer cations for low-dimensional perovskite optoelectronic devices.

Spin-photogalvanic effect in chiral lead halide perovskites

Low-temperature solution-made chiral lead halide perovskites (LHPs) have spontaneous Bychkov-Rashba spin orbit coupling (SOC) and chiral-induced spin selectivity (CISS) qualities. Their coexistence may give rise to considerable spin and charge conversion capabilities for spin-orbitronic applications. In this study, we demonstrate the spin-photogalvanic effect for (R-MBA)₂PbI₄ and (S-MBA)₂PbI₄ polycrystalline film-based lateral devices (100 μm channel length). The light helicity dependence of the short-circuit photocurrent exhibits the circular photogalvanic effect (CPGE) and linear photogalvanic effect (LPGE) with decent two-fold symmetry for a complete cycle in a wide temperature range from 4 K to 300 K. Because of the Rashba SOC and the material helicity, the effect is converse for the two chiral LHPs. In addition, its magnitude and sign can be effectively tuned by constant magnetic fields. The Rashba effect, CISS-generated unbalanced spin transport, and chiral-induced magnetization are mutually responsible for it. Our study evidently proves the future prospect of using chiral LHPs for spin-orbitronics.

Unveiling the degraded electron durability in reduced-dimensional perovskites

The operational stability of reduced-dimensional metal halide perovskites (RD-MHPs) lags far behind the practical requirements for future high-definition displays. Thereinto, the electron durability of RD-MHPs plays a critical role in stable LEDs during continuous operation, however, it still lacks adequate research and a deep understanding. Herein, the electron durability and deterioration mechanism of phenethylammonium (PEA⁺)-modified RD-MHPs are systematically conducted through an in situ photoelectron spectroscopy technique by implementing tunable electron-beam radiation to simulate device operation. The formation of detrimental metallic lead (Pb⁰) caused by the reduction of lead ions (Pb²⁺) is observed along with the decomposition of PEA⁺ under electron-beam radiation, thereby changing the photophysical properties of PEA⁺-doped RD-MHPs. These results provide deep insight into the process of how injected electrons affect the performance of PEA⁺-doped perovskite LEDs, which may also provide potential guidance for designing robust and effective organic spacers for RD-MHPs.

Control of n-Phase Distribution in Quasi Two-Dimensional Perovskite for Efficient Blue Light-Emitting Diodes

Pure-bromide quasi-2D perovskite (PBQ-2DP) promises high-performance light-emitting diodes (LEDs), while a challenge remains on control over its n-phase distribution for bright true-blue emission. Present work addresses the challenge through exploring the passivation molecule of amino acid with reinforced binding energy, which generates narrow n-phase distribution preferentially at n = 3 with true blue emission at 478 nm. Consequently, a peak external quantum efficiency of 5.52% and a record brightness of 512 cd m-2 are achieved on the PBQ-2DP-based true blue PeLED, these both values located among the top in the records of similar devices. We further reveal that the electron-phonon coupling results in the red-shifted emission in the PBQ-2DP film, suggesting that the view of n-phase distribution dominated true-blue emission in PBQ-2DP needs to be revisited, pointing out a guideline of electron-phonon coupling suppression to relieve the strait of realizing true blue or even deep blue emission in the PBQ-2DP film.

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

Perovskites show efficient electroluminescence and are expected to have wide applications in light-emitting diodes (LEDs). However, owing to the unbalanced electron-hole transport properties of some highly luminescent perovskites, a fundamental challenge is that the exciton recombination zone of perovskite LEDs (PeLEDs) typically overlaps with an accumulation of the major carrier. It is known to reduce the performances of PeLEDs, leading to a reduction of efficiency and operation stability due to Auger recombination. To address this issue in a hole-dominated blue PeLED, we propose to insert a cesium acetate (CsAc) layer between the hole transport layer (HTL) and the hole-dominant perovskite layer. Electronic properties indicate that the hole accumulation zone of the device with the CsAc layer shifts away from the perovskite/ETL interface, i.e., the recombination zone, to the HTL/CsAc interface. Separation of the hole accumulation region and the exciton recombination zones substantially suppresses exciton quenching. Moreover, the CsAc layer can also improve the photophysical properties of the perovskite film by providing an extra Cs source to interact with the defect site of unreacted PbBr₂ in the perovskite film and enhance the crystallinity of the perovskite with an enlarged crystal grain size. As a result, the external quantum efficiency (EQE) of the sky-blue PeLEDs shows considerable improvement from 5.3 to 9.2% upon inserting the CsAc layer.