Enhancing the Performance of Perovskite Light-Emitting Diodes via Synergistic Effect of Defect Passivation and Dielectric Screening

Metal halide perovskites,particularly the quasi-two-dimensional perovskite subclass,have exhibited considerable potential for next-generation electroluminescent materials for lighting and display.Nevertheless,the presence of defects within these perovskites has a substantial influence on the emission efficiency and durability of the devices.In this study,we revealed a synergistic passivation mechanism on perovskite films by using a dual-functional compound of potassium bromide.The dual functional potassium bromide on the one hand can passivate the defects of halide vacancies with bromine anions and,on the other hand,can screen the charged defects at the grain boundaries with potassium cations.This approach effectively reduces the probability of carriers quenching resulting from charged defects capture and consequently enhances the radiative recombination efficiency of perovskite thin films,leading to a significant enhancement of photoluminescence quantum yield to near-unity values(95%).Meanwhile,the potassium bromide treatment promoted the growth of homogeneous and smooth film,facilitating the charge carrier injection in the devices.Consequently,the perovskite light-emitting diodes based on this strategy achieve a maximum external quantum efficiency of~21%and maximum luminance of~60,000 cd m^(-2).This work provides a deeper insight into the passivation mechanism of ionic compound additives in perovskite with the solution method.

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.

High-performance flexible perovskite photodetectors based on single-crystal-like two-dimensional Ruddlesden-Popper thin films

Two-dimensional Ruddlesden-Popper(2DRP)perovskites have attracted intense research interest for optoelectronic applications,due to their tunable optoelectronic properties and better environmental stability than their threedimensional counterparts.Furthermore,high-performance photodetectors based on single-crystal and polycrystalline thin-films 2DRP perovskites have shown great potential for practical application.However,the complex growth process of single-crystal membranes and uncontrollable phase distribution of polycrystalline films hinder the further development of 2DRP perovskites photodetectors.Herein,we report a series of high-performance photodetectors based on single-crystal-like phase-pure 2DRP perovskite films by designing a novel spacer source.Experimental and theoretical evidence demonstrates that phase-pure films substantially suppress defect states and ion migration.These highly sensitive photodetectors show I_(light)/I_(dark) ratio exceeding 3×10^(4),responsivities exceeding 16 A/W,and detectivities exceeding 3×10^(13) Jones,which are higher at least by 1 order than those of traditional mixed-phase thinfilms 2DRP devices(close to the reported single-crystal devices).More importantly,this strategy can significantly enhance the operational stability of optoelectronic devices and pave the way to large-area flexible productions.

Surface Passivation Toward Efficient and Stable Perovskite Solar Cells

Although metal halide perovskites are increasingly popular for the next generation of efficient photovoltaic devices,the inevitable defects from the preparation process have become the notorious barrier to further improvement of performance,which increases non-radiative recombination and lowers the power conversion efficiency of solar cells.Surface passivation strategies have been affirmed as one of the most practical approaches to suppress these defects.Therefore,it is necessary to have a detailed review on the surface passivation to reveal the improvements of the devices.Herein,the mechanism and recent advances of surface passivation have been systematically summarized with respect to various passivation approaches,including the Lewis acid–base,the low-dimensional perovskite,inorganic molecules,and polymers.Finally,the review also offers the research trend and prospects of surface passivation.

Phase Regulation and Defect Passivation Enabled by Phosphoryl Chloride Molecules for Efficient Quasi‑2D Perovskite Light‑Emitting Diodes

Quasi-2D perovskites have attracted tremendous interest for application as lightemission layers in light-emitting diodes(LEDs).However,the heterogeneous n phase and non-uniform distribution still severely limit the further development of quasi-2D perovskite LEDs(Pero-LEDs).Meanwhile,the increased defect density caused by the reduced dimension and grain size induces non-radiative recombination and further deteriorates the device performance.Here,we found that a series of molecules containing phosphoryl chloride functional groups have noticeable enhancement effects on the device performance of quasi-2D Pero-LEDs.Then,we studied the modification mechanism by focusing on the bis(2-oxo-3-oxazolidinyl)phosphinic chloride(BOPCl).It is concluded that the BOPCl can not only regulate the phase distribution by decreasing the crystallization rate but also remain in the grain boundaries and passivate the defects.As a result,the corresponding quasi-2D Pero-LEDs obtained a maximum external quantum efficiency(EQE_(max))of 20.82%and an average EQE(EQE_(ave))of around 20%on the optimal 50 devices,proving excellent reproducibility.Our work provides a new selection of molecular types for regulating the crystallization and passivating the defects of quasi-2D perovskite films.

Ecofriendly Hydroxyalkyl Cellulose Additives for Efficient and Stable MAPbI_(3)-Based Inverted Perovskite Solar Cells

Perovskite solar cells(PSCs)have been demonstrated to be one of the most promising technologies in the field of renewable energy.However,the presence of the defects in the perovskite films greatly limits the efficiency and the stability of the PSCs.The additive engineering is one of the most effective approaches to overcome this problem.Most of the successful additives are extracted from the petroleum-based materials,while the research on the biomass-based additives is still lagging behind.In this paper,two ecofriendly hydroxyalkyl cellulose additives,i.e.,hydroxyethyl cellulose(HEC)and hydroxylpropyl cellulose(HPC),are investigated on the performance of the MAPbl_(3)-based inverted PSCs.Due to the strong interaction between the hydroxyl groups of the cellulose and the divalent cations of the perovskite,these additives enhance the crystal grain orientation and significantly repair the defects of the perovskite films.Working as the additives,these two cellulose derivatives show a strong passivation ability,which significantly reduces the trap density and improves the optoelectronic feature of the PSCs.Compared with the average power conversion efficiency(PCE)of the control device(19.19%),an enhancement of~10%is achieved after the addition of HEC.The optimized device(PCE=21.25%)with a long-term stability(10:80 h,PCE=20.93%)is achieved by the incorporation of the HEC additives into the precursor solution.It is the best performance among the PSCs with the cellulose additives up to now.This research provides a novel choice to develop a cost-effective and renewable additive for the PSCs with high efficiency and excellent long-term stability.

Functional Janus Membranes:Promising Platform for Advanced Lithium Batteries and Beyond

Separators or electrolyte membranes are recognized as the key components to guarantee ion transport in rechargeable batteries.However,the ever-growing applications of the battery systems for diverse working environments bring new challenges,which require advanced battery membranes with high thermal stability,excellent mechanical strength,high voltage tolerance,etc.Therefore,it is highly desirable to design novel methods/concepts to solve the current challenges for battery membranes through understanding the mechanism of novel phenomena and electrochemical reactions in battery systems working under unconventional conditions.Recently,the new emerging Janus separators or electrolyte membranes with two or more distinct chemical/physical properties arising from their asymmetric structure and composition,are promising to address the above challenges via rational design of their targeted functionalities.To this end,in this review,we first briefly cover the current challenges of the traditional battery membrane for battery devices working in unconventional conditions.Then,the state-of-art developments of the rational design of Janus membranes to overcome the above challenges for diverse battery applications are summarized.Finally,we outline these latest developments,challenges,and future potential directions of the Janus membrane.Our review is aimed to provide basic guidance for developing functional separators or electrolyte membranes for advanced batteries.

Band structure engineering in metal halide perovskite nanostructures for optoelectronic applications

Metal halide perovskite nanostructures have emerged as low-dimensional semiconductors of great significance in many fields such as photovoltaics,photonics,and optoelectronics.Extensive efforts on the controlled synthesis of perovskite nanostructures have been made towards potential device applications.The engineering of their band structures holds great promise in the rational tuning of the electronic and optical properties of perovskite nanostructures,which is one of the keys to achieving efficient and multifunctional optoelectronic devices.In this article,we summarize recent advances in band structure engineering of perovskite nanostructures.A survey of bandgap engineering of nanostructured perovskites is firstly presented from the aspects of dimensionality tailoring,compositional substitution,phase segregation and transition,as well as strain and pressure stimuli.The strategies of electronic doping are then reviewed,including defect-induced self-doping,inorganic or organic molecules-based chemical doping,and modification by metal ions or nanostructures.Based on the bandgap engineering and electronic doping,discussions on engineering energy band alignments in perovskite nanostructures are provided for building high-performance perovskite p-n junctions and heterostructures.At last,we provide our perspectives in engineering band structures of perovskite nanostructures towards future low-energy optoelectronics technologies.

Residual solvent extraction via chemical displacement for efficient and stable perovskite solar cells

Solvent residue is inevitable to occur in solution processed thin films,but its influence on the thin film quality has not been identified and addressed to date.Methylammonium acetate(MAAc)ionic liquid has recently been realized as an environmentally friendly solvent for solution processed perovskites.The specific high viscosity,low vapor pressure and strong association with perovskite precursor of the MAAc solvent is a double-edged sword,which endowed an advantageously ambient air operational and anti-solvent free perovskite deposition,but the MAAc is likely to be retained within the film and bring in detrimental effects on device performance of the corresponding solar cells.Herein,we reported a novel route to eliminate the residual solvent via a facial hydrochloric acid(HCl)annealing post-treatment(HAAP).In particular,chemical displacement reaction between the incorporated HCl and residual MAAc can be initiated to form volatile MACl and HAc,efficiently extracting MAAc residue.In the meanwhile,the stimulated mass transport via downward penetration and upward escape can trigger secondary perovskite growth with enlarged grain size and smoothened surface,leading to reduced defect state and improved interfacial contact intimacy,and also partial chloride ions are able to enter the crystal lattice to stabilize perovskite phase structure.As a result,a champion efficiency up to20.78%originating from enhanced Voc was achieved,and more than 96%of its initial efficiency can be maintained after 1000 h shelf-storage.

Ruddlesden–Popper Perovskite for Stable Solar Cells

Three-dimensional metal-halide perovskites have emerged as promising light harvesting materials for converting sunlight to electricity in the last few years.High power conversion efficiency of 23.3%has been demonstrated.However,the main challenge that currently limits the application of the perovskite solar cells is the long-term stability,which has ambient,thermal,and photo stability weaknesses.

Chiral cation promoted interfacial charge extraction for efficient tin-based perovskite solar cells

Pb-free Sn-based perovskite solar cells(PSCs) have recently made inspiring progress, and power conversion efficiency(PCE) of 14.8% has been achieved. However, due to the energy-level mismatch and poor interfacial contact between commonly used hole transport layer(i.e., poly(3,4-ethylenedioxythio phene):poly(styrene sulfonate), PEDOT:PSS) and FASnI_(3) film, it is still challenging to effectively extract holes at the interface. Owing to the p-type nature of Sn-based perovskites, the efficient hole extraction is of particular significance to improve the PCE of their solar cells. In this work, for the first time, the role of chiral cations, a-methylbenzylamine(S-/R-/rac-MBA), in promoting hole transportation of FASnI_(3)-based PSCs is demonstrated. The introduction of MBAs is found to form 2D/3D film with lowdimensional structures locating at PEDOT:PSS/FASnI_(3) interface, which facilitates the energy level alignment and efficient charge transfer at the interface. Importantly, chiral-induced spin selectivity(CISS)effect of R-MBA_(2)SnI_(4)induced by chiral R-MBA cation is found to further assist the specific interfacial transport of accumulated holes. As a result, R-MBA-based PSCs achieve decent PCE of 10.73% with much suppressed hysteresis and enhanced device stability. This work opens up a new strategy to efficiently promote the interfacial extraction of accumulated charges in working PSCs.

Overcoming the Limitation of Cs_(2)AgBiBr_(6) Double Perovskite Solar Cells Through Using Mesoporous TiO_(2) Electron Extraction Layer

Lead-free double perovskite Cs_(2)AgBiBr_(6) has gained increasing attention recently.However,the power conversion efficiency(PCE)of Cs_(2)AgBiBr_(6) perovskite solar cells(PSCs)is still low compared with their lead-based counterparts.Here,by using photoluminescence(PL),time-resolved photoluminescence(TRPL),and ultrafast transient absorption(TA)measurements,the unbalance between the electron and hole in diffusion and transfer,which limits the performance of the Cs_(2)AgBiBr_(6) PSCs,was further revealed.Considering this issue,a strategy of using the mesoporous TiO_(2) electron transport layer(ETL)to construct a bulk heterojunction in Cs_(2)AgBiBr_(6) PSCs was proposed.Consequently,the PCE had improved by over 24%comparing with that only used compact TiO_(2) ETL.Moreover,based on mesoporous TiO_(2),the unencapsulated Cs_(2)AgBiBr_(6) PSCs maintained 90%of their initial performance after approximately 1200 h of storage in a desiccator(humidity~30%).This work gives further understanding of Cs_(2)AgBiBr_(6) perovskite and demonstrates that a proper design of balancing the electron and hole diffusion can improve device performance.

Doping Electron Transporting Layer:An Effective Method to Enhance J_(SC)of All-Inorganic Perovskite Solar Cells

All-inorganic metal-halide CsPbBr_(3)perovskite has emerged as an attractive photovoltaic material for its outstanding environmental stability.However,due to the wide bandgap,the performance of CsPbBr_(3)perovskite solar cells(PSCs)is limited,especially for the short-circuit current density(J_(SC)).In this issue of Energy&Environmental Materials,Guo et al.employed Nb-doped SnO_(2)as electron transporting layers(ETLs),which could greatly improve the J_(SC)of the PSCs based on all-inorganic CsPbBr_(3).

Regulation of the multi-emission centers in carbon dots via a bottom-up synthesis approach

Understanding the luminescence mechanisms and regulating the emission centers of carbon dots(CDs)are important for advancing their related applications.In this work,we systematically investigate the formation processes of multi-emission centers in CDs synthesized through a bottom-up approach by controlling the solvothermal reaction temperature.CDs synthesized at a lower temperature(140℃,140-CDs)exhibit smaller particle sizes(3–4 nm)with dominant green–yellow emission,while CDs synthesized at a higher temperature(180℃,180-CDs)exhibit larger particle sizes(8–9 nm)with enhanced red emission and emerging near-infrared(NIR)emission.The green–yellow emission and red emission originate from the core state and the surface-related state,respectively,and the emissions could be regulated by temperature-controlled dehydration and carbonization processes.The clear NIR emission center in 180-CDs is attributable to the increased content of radical defects in the cores during the increased dehydration and carbonization processes during higher-temperature solvothermal treatment.

Benzothiadiazole-based materials for organic solar cells

The past few years have witnessed power conversion efficiency(PCE)of organic solar cells(OSCs)skyrocketing to the value of 20%due to the outstanding advantages of organic photoactive materials.The latter,which consist of donor and acceptor materials,indeed play important roles in OSCs,and particularly one building block has attracted considerable research attention,namely benzothiadiazole(BT).The diversity of OSCs based on the BT structure have indeed sprung up,and the progressive increase in PCE values is more than just eye-catching since it heralds a renewal and bright future of OSCs.This review analyzes significant studies that have led to these remarkable progresses and focuses on the most effective BT small-molecules and BT polymers for OSC reported in the last decades.The pivotal structure-property relationships,donor-acceptor matching criteria,and morphology control approaches are gathered and discussed in this paper.Lastly,we summarize the remaining challenges and offer a personal perspective on the future advance and improvement of OSCs.

Nanoscale phase management of the 2D/3D heterostructure toward efficient perovskite solar cells

The stabilization of the formamidinium lead iodide(FAPbI_(3))structure is pivotal for the development of efficient photovoltaic devices.Employing two-dimensional(2D)layers to passivate the threedimensional(3D)perovskite is essential for maintaining the a-phase of FAPbI_(3) and enhancing the power conversion efficiency(PCE)of perovskite solar cells(PSCs).However,the role of bulky ligands in the phase management of 2D perovskites,crucial for the stabilization of FAPbI_(3),has not yet been elucidated.In this study,we synthesized nanoscale 2D perovskite capping crusts with<n>=1 and 2 Ruddlesden-Popper(RP)perovskite layers,respectively,which form a type-Ⅱ 2D/3D heterostructure.This heterostructure stabilizes the a-phase of FAPbI_(3),and facilitates ultrafast carrier extraction from the 3D perovskite network to transport contact layer.We introduced tri-fluorinated ligands to mitigate defects caused by the halide vacancies and uncoordinated Pb^(2+)ions,thereby reducing nonradiative carrier recombination and extending carrier lifetime.The films produced were incorporated into PSCs that not only achieved a PCE of 25.39%but also maintained 95%of their initial efficiency after 2000 h of continuous light exposure without encapsulation.These findings underscore the effectiveness of a phase-pure 2D/3D heterostructure-terminated film in inhibiting phase transitions passivating the iodide anion vacancy defects,facilitating the charge carrier extraction,and boosting the performance of optoelectronic devices.

Homogeneous permeation and oriented crystallization in nanostructured mesopores for efficient and stable printable mesoscopic perovskite solar cells

The low-cost and scalable printable mesoporous perovskite solar cells(p-MPSCs) face significant challenges in regulating perovskite crystal growth due to their nanoscale mesoporous scaffold structure, which limits the improvement of device power conversion efficiency(PCE). In particular, the most commonly used solvents, N,N-dimethylformamide(DMF) and dimethyl sulfoxide(DMSO), have a single chemical interaction with the precursor components and high volatility, which is insufficient to self-regulate the perovskite crystallization process, leading to explosive nucleation and limited growth within mesoporous scaffolds. Here, we report a mixed solvent system composed of methylamine formaldehyde(MAFa)-based ionic liquid and acetonitrile(ACN) with the strong C=O–Pb coordination and N–H···I hydrogen bonding with perovskite components. We found that the mixed solvent system is beneficial for the precursor solution to homogeneously penetrate into the mesoporous scaffold,and the strong C=O–Pb coordination and N–H···I hydrogen bonding interaction can promote the oriented growth of perovskite crystals. This synergistic effect increased the PCE of the p-MPSCs from 17.50% to 19.21%, which is one of the highest records for p-MPSC in recent years. Additionally, the devices exhibit positive environmental stability, retaining over 90% of the original PCE after 1,200 h of aging under AM 1.5 illumination conditions at 55 ℃ and 55% humidity.

Revitalizing sodium-ion batteries via controllable microstructures and advanced electrolytes for hard carbon

Sodium-ion batteries(SIBs)with low cost and high safety are considered as an electrochemical energy storage technology suitable for large-scale energy storage.Hard carbon,which is inexpensive and has both high capacity and low sodium storage potential,is regarded as the most promising anode for commercial SIBs.However,the commercialization of hard carbon still faces technical issues of low initial Coulombic efficiency,poor rate performance,and insufficient cycling stability,due to the intrinsically irregular microstructure of hard carbon.To address these challenges,the rational design of the hard carbon microstructure is crucial for achieving high-performance SIBs,via gaining an in-depth understanding of its structure-performance correlations.In this context,our review firstly describes the sodium storage mechanism from the perspective of the hard carbon microstructure's formation.We then summarize the state-of-art development of hard carbon,providing a critical overview of emergence of hard carbon in terms of precursor selection,microstructure design,and electrolyte regulation to optimize strategies for addressing practical problems.Finally,we highlight directions for the future development of hard carbon to achieve the commercialization of high-performance SIBs.We believe this review will serve as basic guidance for the rational design of hard carbon and stimulate more exciting research into other types of energy storage devices.

Chelation strategy induced blue-shift for efficient deep-blue perovskite light-emitting diodes

Metal halide perovskite, regarded as a potential material for next-generation display and lighting applications, has attracted great attention [1,2]. The development of blue perovskite light-emitting diodes (Pe LEDs) remains stagnant compared with their green and red counterparts in recent years [3–8].

Pulse-doubling perovskite nanowire lasers enabled by phonon-assisted multistep energy funneling

Laser pulse multiplication from an optical gain medium has shown great potential in miniaturizing integrated optoelectronic devices.Perovskite multiple quantum wells(MQWs)structures have recently been recognized as an effective gain media capable of doubling laser pulses that do not rely on external optical equipment.Although the light amplifications enabled with pulse doubling are reported based on the perovskite MQWs thin films,the micronanolasers possessed a specific cavity for laser pulse multiplication and their corresponding intrinsic laser dynamics are still inadequate.Herein,a single-mode double-pulsed nanolaser from self-assembled perovskite MQWs nanowires is realized,exhibiting a pulse duration of 28 ps and pulse interval of 22 ps based on single femtosecond laser pulse excitation.It is established that the continuous energy building up within a certain timescale is essential for the multiple population inversion in the gain medium,which arises from the slowing carrier localization process owning to the stronger exciton–phonon coupling in the smaller-n QWs.Therefore,the double-pulsed lasing is achieved from one fast energy funnel process from the adjacent small-n QWs to gain active region and another slow process from the spatially separated ones.This report may shed new light on the intrinsic energy relaxation mechanism and boost the further development of perovskite multiple-pulse lasers.