A Systematic Approach to Achieving High Performance Hybrid Lighting Phosphors with Excellent Thermal‐ and Photostability

The authors have designed and synthesized a family of high‐performance inorganic–organic hybrid phosphor materials composed of extended and robust networks of one, two, and three dimensions. Following a bottom‐up solution‐based synthetic approach, these structures are constructed by connecting highly emissive Cu₄I₄ cubic clusters via carefully selected ligands that form strong Cu? N bonds. They emit intensive yellow‐orange light with high luminescence quantum efficiency, coupled with large Stokes shift, which greatly reduces self‐absorption. They also demonstrate exceptionally high framework‐ and photostability, comparable to those of commercial phosphors. The high stabilities are the result of significantly enhanced Cu? N bonds, as confirmed by the density functional theory (DFT) binding energy and electron density calculations. Possible emission mechanisms are analyzed based on the results of theoretical calculations and optical experiments. Two‐component white phosphors obtained by blending blue and yellow emitters reach an internal quantum yield as high as 82% and correlated color temperature as low as 2534 K. The performance level of this subfamily exceeds all other types of Cu–I based hybrid systems. The combined advantages make them excellent candidates as alternative rare‐earth element‐free phosphors for possible use in energy‐efficient lighting devices.     

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

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

Efficient Perovskite Hybrid Solar Cells via Ionomer Interfacial Engineering

The surface of the solution‐processed methylammonium lead tri‐iodide (CH₃NH₃PbI₃) perovskite layer in perovskite hybrid solar cells (pero‐HSCs) tends to become rough during operation, which inevitably leads to deterioration of the contact between the perovskite layer and the charge‐extraction layers. Moreover, the low electrical conductivity of the electron extraction layer (EEL) gives rises to low electron collection efficiency and severe charge carrier recombination, resulting in energy loss during the charge‐extraction and ‐transport processes, lowering the efficiency of pero‐HSCs. To circumvent these problems, we utilize a solution‐processed ultrathin layer of a ionomer, 4‐lithium styrenesulfonic acid/styrene copolymer (LiSPS), to re‐engineer the interface of CH₃NH₃PbI₃ in planar heterojunction (PHJ) pero‐HSCs. As a result, PHJ pero‐HSCs are achieved with an increased photocurrent density of 20.90 mA cm^?2, an enlarged fill factor of 77.80%, a corresponding enhanced power conversion efficiency of 13.83%, high reproducibility, and low photocurrent hysteresis. Further investigation into the optical and electrical properties and the thin‐film morphologies of CH₃NH₃PbI₃ with and without LiSPS, and the photophysics of the pero‐HSCs with and without LiSPS are shown. These demonstrate that the high performance of the pero‐HSCs incorporated with LiSPS can be attributed to the reduction in both the charge carrier recombination and leakage current, as well as more efficient charge carrier collection, filling of the perforations in CH₃NH₃PbI_3, and a higher electrical conductivity of the LiSPS thin layer. These results demonstrate that our method provides a simple way to boost the efficiency of pero‐HSCs.     

Spontaneous Hybrid Nano-Domain Behavior of the Organic–Inorganic Hybrid Perovskites

In hybrid perovskites, the organic molecules and inorganic frameworks exhibit distinct static and dynamic characteristics. Their coupling will lead to fascinating phenomena, such as large polarons, dynamic Rashba–Dresselhaus effects, etc. In this paper, deep potential molecular dynamics (DPMD) is employed, a large-scale MD simulation scheme with DFT accuracy, to study hybrid perovskites formamidinium lead iodide (FAPbI₃) and methylamonium lead iodide (MAPbI₃). A spontaneous hybrid nano-domain behavior, namely multiple molecular rotation nano-domains embedded into a single [PbI₆]⁴⁻ octahedra rotation domain, is first discovered at low temperatures. The behavior originates from the interplay between the long range order of molecular rotation and local lattice deformation, and clarifies the puzzling structural features of FAPbI₃ at low temperatures. The work provides new insights into the structural characteristics and stability of hybrid perovskite, as well as new ideas for the structural characterization of organic–inorganic coupled systems.     

Interplay of Structural and Optoelectronic Properties in Formamidinium Mixed Tin–Lead Triiodide Perovskites

Mixed lead–tin triiodide perovskites are promising absorber materials for low bandgap bottom cells in all‐perovskite tandem photovoltaic devices. Key structural and electronic properties of the FAPb_1−xSn_xI₃ perovskite are presented here as a function of lead:tin content across the alloy series. Temperature‐dependent photoluminescence and optical absorption measurements are used to identify changes in the bandgap and phase transition temperature. The large bandgap bowing parameter, a crucial element for the attainment of low bandgaps in this system, is shown to depend on the structural phase, reaching a value of 0.84 eV in the low‐temperature phase and 0.73 eV at room temperature. The parabolic nature of the bowing at all temperatures is compatible with a mechanism arising from bond bending to accommodate the random placement of unevenly sized lead and tin ions. Charge‐carrier recombination dynamics are shown to fall into two regimes. Tin‐rich compositions exhibit fast, monoexponential recombination that is almost temperature‐independent, in accordance with high levels of electrical doping. Lead‐rich compositions show slower, stretched‐exponential charge‐carrier recombination that is strongly temperature‐dependent, in accordance with a multiphonon assisted process. These results highlight the importance of structure and composition for control of bandgap bowing and charge‐carrier recombination mechanisms in low bandgap absorbers for all‐perovskite tandem solar cells.     

Efficient and Ambient‐Air‐Stable Solar Cell with Highly Oriented 2D@3D Perovskites

3D organic–inorganic lead halide perovskites have shown great potential in efficient photovoltaic devices. However, the low stability of the 3D perovskite layer and random arrangement of the perovskite crystals hinder its commercialization road. Herein, a highly oriented 2D@3D ((AVA)₂PbI₄@MAPbI₃) perovskite structure combining the advantages of both 2D and 3D perovskite is fabricated through an in situ route. The highest power conversion efficiency (PCE) of 18.0% is observed from a 2D@3D perovskite solar cell (PSC), and it also shows significantly enhanced device stability under both inert (90% of initial PCE for 32 d) and ambient conditions (72% of initial PCE for 20 d) without encapsulation. The high efficiency of 18.0% and nearly twofold improvement of device stability in ambient compared with pure 3D PSCs confirm that such 2D@3D perovskite structure is an effective strategy for high performance and increasing stability and thus will enable the timely commercialization of PSCs.     

Unique Seamlessly Bonded CNT@Graphene Hybrid Nanostructure Introduced in an Interlayer for Efficient and Stable Perovskite Solar Cells

Carbon nanomaterials have been widely used as an interlayer for realizing efficient and stable perovskite solar cells (PSCs). Theoretically, the design of a carbon composite interlayer that combines excellent conductivity with a high specific surface area is a better strategy than the application of pure nanocarbons. Here, an unusual seamlessly bonded carbon nanotube@graphene (CNT@G) hybrid nanomaterial was strategically synthesized and demonstrated to behave as an efficient interlayer for realizing efficient and stable PSCs. Due to the advantage of the seamless bond, the as‐proposed hybrid nanostructure showed an apparent improvement compared to the use of CNTs only, graphene only, or a simple mixture of CNTs and graphene. The power conversion efficiency improved from 15.67% to 19.56% after introduction of the hybrid nanomaterial due to efficient carrier extraction, faster charge transport, and restrained carrier recombination. More importantly, PSCs with a CNT@G hybrid‐decorated hole transport layer (HTL) showed good thermal stability during a 50 h heat‐aging test at 100 °C and water stability under ambient humidity (30–50% relative humidity) for 500 h because the hybrid nanostructure exhibited an increased capability to block ion/molecule diffusion. Our results provide an alternative approach for fully exploring the potential application of nanocarbons in the development of high‐performance PSCs.     

Formamidinium‐Based Dion‐Jacobson Layered Hybrid Perovskites: Structural Complexity and Optoelectronic Properties

Layered hybrid perovskites have emerged as a promising alternative to stabilizing hybrid organic–inorganic perovskite materials, which are predominantly based on Ruddlesden‐Popper structures. Formamidinium (FA)‐based Dion‐Jacobson perovskite analogs are developed that feature bifunctional organic spacers separating the hybrid perovskite slabs by introducing 1,4‐phenylenedimethanammonium (PDMA) organic moieties. While these materials demonstrate competitive performances as compared to other FA‐based low‐dimensional perovskite solar cells, the underlying mechanisms for this behavior remain elusive. Here, the structural complexity and optoelectronic properties of materials featuring (PDMA)FA_n–1Pb_nI_3n+1 (n = 1–3) formulations are unraveled using a combination of techniques, including X‐ray scattering measurements in conjunction with molecular dynamics simulations and density functional theory calculations. While theoretical calculations suggest that layered Dion‐Jacobson perovskite structures are more prominent with the increasing number of inorganic layers (n), this is accompanied with an increase in formation energies that render n > 2 compositions difficult to obtain, in accordance with the experimental evidence. Moreover, the underlying intermolecular interactions and their templating effects on the Dion‐Jacobson structure are elucidated, defining the optoelectronic properties. Consequently, despite the challenge to obtain phase‐pure n > 1 compositions, time‐resolved microwave conductivity measurements reveal high photoconductivities and long charge carrier lifetimes. This comprehensive analysis thereby reveals critical features for advancing layered hybrid perovskite optoelectronics.     

Copper Iodide Based Hybrid Phosphors for Energy‐Efficient General Lighting Technologies

Solid‐state‐lighting (SSL) is a new lighting technology that is rapidly replacing conventional lighting sources because it is much more energy efficient, longer lasting, and contributes significantly to environmental protection. A main branch of SSL technology is light‐emitting diodes (LEDs), and white‐light LEDs (WLEDs) are in the greatest demand for general lighting and illumination applications. Current WLED devices rely heavily on rare‐earth elements (REEs), which will likely suffer from cost and supply risks and environmental consequences in the near future. Crystalline inorganic–organic hybrid materials based on I–VII binary semiconductors represent a promising material class as REE‐free phosphor alternatives. This article provides a brief overview of recent advancement on this material family, with a focus on the rational design, energy‐efficient and low‐cost synthesis, systematic modification, and optimization of their electronic, optical, and thermal properties. A particular emphasis will be made on our own progress over the past several years in developing four classes of CuI(L) structures with substantially improved performance as energy‐saving lighting phosphors. General strategies for structural design, synthesis, and property optimization of these materials will also be discussed.     

Defects in Hybrid Perovskites: The Secret of Efficient Charge Transport

The interaction of free carriers with defects and some critical defect properties are still unclear in methylammonium lead halide perovskites (MHPs). Here, a multi-method approach is used to quantify and characterize defects in single crystal MAPbI₃, giving a cross-checked overview of their properties. Time of flight current waveform spectroscopy reveals the interaction of carriers with five shallow and deep defects. Photo-Hall and thermoelectric effect spectroscopy assess the defect density, cross-section, and relative (to the valence band) energy. The detailed reconstruction of free carrier relaxation through Monte Carlo simulation allows for quantifying the lifetime, mobility, and diffusion length of holes and electrons separately. Here, it is demonstrated that the dominant part of defects releases free carriers after trapping; this happens without non-radiative recombination with consequent positive effects on the photoconversion and charge transport properties. On the other hand, shallow traps decrease drift mobility sensibly. The results are the key for the optimization of the charge transport properties and defects in MHP and contribute to the research aiming to improve perovskite stability. This study paves the way for doping and defect control, enhancing the scalability of perovskite devices with large diffusion lengths and lifetimes.     

Spatial Charge Separation as the Origin of Anomalous Stark Effect in Fluorous 2D Hybrid Perovskites

2D hybrid perovskites (2DP) are versatile materials, whose electronic and optical properties can be tuned through the nature of the organic cations (even when those are seemingly electronically inert). Here, it is demonstrated that fluorination of the organic ligands yields glassy 2DP materials featuring long‐lived correlated electron–hole pairs. Such states have a marked charge‐transfer character, as revealed by the persistent Stark effect in the form of a second derivative in electroabsorption. Modeling shows that electrostatic effects associated with fluorination, combined with the steric hindrance due to the bulky side groups, drive the formation of spatially dislocated charge pairs with reduced recombination rates. This work enriches and broadens the current knowledge of the photophysics of 2DP, which will hopefully guide synthesis efforts toward novel materials with improved functionalities.     

Constructing All-Inorganic Perovskite/Fluoride Nanocomposites for Efficient and Ultra-Stable Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells (PSCs) have rapidly developed over the past decade and have achieved the latest certified power conversion efficiency (PCE) up to 25.5%. However, unsatisfactory long-term operational stability for these hybrid PSCs remains a huge obstacle to further development and commercialization. Herein, a unique hetero-structured CsPbI₃/CaF₂ perovskite/fluoride nanocomposites (PFNCs) is fabricated via a newly developed facile two-step hetero-epitaxial growth strategy to deliver efficient and ultra-stable PSCs. After being incorporated into the crystal lattice of α-phase CsPbI₃ perovskite, the cubic-phase CaF₂ in the resultant CsPbI₃/CaF₂ PFNCs can not only passivate the intrinsic defects of CsPbI₃ perovskite itself but also effectively suppress the notorious ion migration in hybrid perovskite Cs_0.05FA_0.81MA_0.14PbI_2.55Br_0.45 (CsFAMA) thin-films of PSCs. As such, the CsFAMA PSC devices based on CsPbI₃/CaF₂-deposited perovskite thin-film achieve a mean PCE of 20.45%, in sharp contrast to 19.33% of the control devices without deposition. Specifically, the CsPbI₃/CaF₂-deposited PSC retains 85% of its original PCE after 1000 h continuous operation at the maximum power point under AM 1.5G solar light, far better than those of the control and CsPbI₃-deposited PSCs with a device T₈₅ lifetime of 315 and 125 h, respectively.     

Quasi‐2D Inorganic CsPbBr3 Perovskite for Efficient and Stable Light‐Emitting Diodes

Metal halide perovskites are rising as a competitive material for next‐generation light‐emitting diodes (LEDs). However, the development of perovskite LEDs is impeded by their fast carriers diffusion and poor stability in bias condition. Herein, quasi‐2D CsPbBr₃ quantum wells homogeneously surrounded by inorganic crystalline Cs₄PbBr₆ of large bandgap are grown. The centralization of carriers in nanoregion facilitates radiative recombination and brings much enhanced luminescence quantum yield. The external quantum efficiency and luminescence intensity of the LEDs based on this nanocomposite are one order of magnitude higher than the conventional low‐dimensional perovskite. Meanwhile, the use of inorganic nanocomposite materials brings much improved device operation lifetime under constant electrical field.     

Hybrid White Light Emitting Diode Based on Silicon Nanocrystals

A novel design of white light emitting diodes (WLEDs) emerges to meet the growing global demand for resource sustainability while preserving health and environment. To achieve this goal, a facile method is developed for the chemical synthesis of a luminescent silicon nanocrystal (ncSi) with a large Stokes shift between absorption and emission. The WLED is prepared by a simple spin‐coating method, and contains a hybrid‐bilayer of the ncSi and luminescent polymer in its device active region. Interestingly, a well‐controlled ultrathin ncSi layer on the polymer makes possible to recombine electrons and holes in both layers, respectively. Combining red and blue‐green lights, emitted from the ncSi and the polymer layers, respectively, produces the emission of white electroluminescence. Herein, a hybrid‐WLED with a sufficiently low turn‐on voltage (3.5 V), produced by taking advantages of the large Stokes shift inherent in ncSi, is demonstrated.     

Amine‐Free Synthesis of Cesium Lead Halide Perovskite Quantum Dots for Efficient Light‐Emitting Diodes

Cesium lead halide perovskite quantum dots (PQDs) have attracted significant interest for optoelectronic applications in view of their high brightness and narrow emission linewidth at visible wavelengths. A remaining challenge is the degradation of PQDs during purification from the synthesis solution. This is attributed to proton transfer between oleic acid and oleylamine surface capping agents that leads to facile ligand loss. Here, a new synthetic method is reported that enhances the colloidal stability of PQDs by capping them solely using oleic acid (OA). Quaternary alkylammonium halides are used as precursors, eliminating the need for oleylamine. This strategy enhances the colloidal stability of OA capped PQDs during purification, allowing us to remove excess organic content in thin films. Inverted red, green, and blue PQD light‐emitting diodes (LED) are fabricated for the first time with solution‐processed polymer‐based hole transport layers due to higher robustness of OA capped PQDs to solution processing. The blue and green LEDs exhibit threefold and tenfold improved external quantum efficiency (EQE), respectively, compared to prior related reports for amine/ammonium capped cross‐linked PQDs. The brightest blue LED based on all inorganic CsPb(Br_1?xCl_x)₃ PQDs is also reported.     

Coherent Phonon-Induced Modulation of Charge Transfer in 2D Hybrid Perovskites

Electron–phonon interactions play an essential role in charge transport and transfer processes in semiconductors. For most structures, tailoring electron–phonon interactions for specific functionality remains elusive. Here, it is shown that, in hybrid perovskites, coherent phonon modes can be used to manipulate charge transfer. In the 2D double perovskite, (AE2T)₂AgBiI₈ (AE2T: 5,5“-diylbis(amino-ethyl)-(2,2”-(2)thiophene)), the valence band maximum derived from the [Ag_0.5Bi_0.5I₄]^2– framework lies in close proximity to the AE2T-derived HOMO level, thereby forming a type-II heterostructure. During transient absorption spectroscopy, pulsed excitation creates sustained coherent phonon modes, which periodically modulate the associated electronic levels. Thus, the energy offset at the organic–inorganic interface also oscillates periodically, providing a unique opportunity for modulation of interfacial charge transfer. Density-functional theory corroborates the mechanism and identifies specific phonon modes as likely drivers of the coherent charge transfer. These observations are a striking example of how electron–phonon interactions can be used to manipulate fundamentally important charge and energy transfer processes in hybrid perovskites.     

Spacer Cation Tuning Enables Vertically Oriented and Graded Quasi-2D Perovskites for Efficient Solar Cells

Halide substitution in phenethylammonium spacer cations (X-PEA⁺, X  = F, Cl, Br) is a facile strategy to improve the performance of PEA based perovskite solar cells (PSCs). However, the power conversion efficiency (PCE) of X-PEA based quasi-2D (Q-2D) PSCs is still unsatisfactory and the underlying mechanisms are in debate. Here, the in-depth study on the impact of halide substitution on the crystal orientation and multi-phase distribution in PEA based perovskite films are reported. The halide substitution eliminates n  =  1 2D perovskite and thus leads to the perpendicular crystal orientation. Furthermore, nucleation competition exists between small-n and large-n phases in PEA and X-PEA based perovskites. This gives rise to the orderly distribution of different n-phases in the PEA and F-PEA based films, and random distribution in Cl-PEA and Br-PEA based films. As a result, (F-PEA)₂MA₃Pb₄I₁₂ (MA = CH₃NH₃⁺, n = 4) based PSCs achieve a PCE of 18.10%, significantly higher than those of PEA (12.23%), Cl-PEA (7.93%) and Br-PEA (6.08%) based PSCs. Moreover, the F-PEA based devices exhibit remarkably improved stability compared to their 3D counterparts.     

提高基于粉浆法的功率型白光LEDs发光效率的研究

基于水溶性感光胶的白光LEDs平面涂层技术,在蓝光LED芯片表面上得到了可控的荧光粉层.采用降低粉浆中ADC的浓度和提高荧光粉的含量两种措施,减少Cr3+在433.6和620nm两处吸收对器件出光效率的影响;新配制的粉浆在暗室中静置3～5h,既可以提高器件的出光效率同时又避免了暗反应带来的影响;在蓝光LED表面上得到粉层后,再涂覆硅胶层,由于硅胶的折射率与粉层的更接近,不但使出光色调偏向蓝光区域而且有更多光子出射,光通量由未加硅胶层时的44.8～59 lm提高到了79.4～84.9 lm.     

提高基于粉浆法的功率型白光LEDs发光效率的研究

基于水溶性感光胶的自光LEDs平面涂层技术,在蓝光LED芯片表面上得到了可控的荧光粉层．采用降低粉浆中ADC的浓度和提高荧光粉的含量两种措施,减少Cr^3＋在433．6和620nm两处吸收对器件出光效率的影响;新配制的粉浆在暗室中静置3～5h,既可以提高器件的出光效率同时又避免了暗反应带来的影响;在蓝光LED表面上得到粉层后,再涂覆硅胶层,由于硅胶的折射率与粉层的更接近,不但使出光色调偏向蓝光区域而且有更多光子出射,光通量由未加硅胶层时的44．8～59lm提高到了79．4～84．9lm．