Mixed Halide Perovskite Films Research Articles

Phosphonic Chloride Assisted Fabrication of Highly Emissive Mixed Halide Perovskite Films in Ambient Air for Blue Light-Emitting Diodes.

Blue perovskite light-emitting diodes (LEDs) have emerged as promising candidates for full-color display and lighting applications. However, the fabrication of blue-emitting perovskite films typically requires an inert environment, leading to increased complexity and cost in the manufacturing process, which is undesirable for applications of perovskite LEDs. Herein, we report a strategy to fabricate bright blue-emitting perovskite films in ambient air by incorporating phosphonic chlorides in a perovskite precursor solution. We used two different phosphonic chlorides, diphenylphosphonic chloride (DPPC) and phenylphosphonic dichloride (PPDC), and comparatively studied their effects on the properties of perovskite films and the blue LEDs. It is found that PPDC possesses a stronger chlorination ability due to higher hydrolysis reactivity; meanwhile, it has a stronger interaction with the perovskite compared to DPPC, resulting in an improved film quality and enhanced blue emission with a photoluminescence quantum yield of 45%, which represents the record value for the air-processed blue perovskite films. Blue perovskite LEDs are fabricated, and the emission wavelengths are effectively tuned by controlling the concentration of phosphonic chlorides. Benefiting from the optimized perovskite films with reduced nonradiative recombination and promoted charge injection and transport, the PPDC-derived blue perovskite LEDs exhibit improved performance with an external quantum efficiency of 3.3% and 1.2% for the 490 and 480 nm emission wavelength, respectively.

The impact of bi-doped on MAPb(IxBr1–x)3 mixed halide perovskite films

Perovskite solar cells have attracted considerable attention from researchers owing to their cost-effective manufacturing processes, facilitating their suitability for commercialization. Halide perovskite such as methylammonium lead iodide (MAPbI3), methylammonium lead bromide (MAPbBr3) and other mixed halide perovskite are intensively studied as light absorber for solar cells. In order to adjust the properties of the perovskite, doping with heterovalent metal ions such as bismuth iodide, BiI3, has demonstrated notable impact on both crystal structure and optical properties. Traditionally, Bi3+ doping has been conducted primarily in single halide perovskite. However, our study explored the possibility of Bi3+ doping at a concentrations of 5% in mixed halide perovskite, specifically the mixed iodide-bromide perovskite, MAPb(IxBr1–x)3 at x = 0.2, 0.4, 0.6 and 0.8. The XRD results revealed a decrease in lattice constant upon Bi3+ doping which likely attributed to the smaller ionic radius of Bi3+ compared to Pb2+. The light absorption spectra of Bi3+ doping perovskites exhibited a significant red shift compared to the undoped samples. The presences of the key elements are confirmed by photoemission spectroscopy results. Moreover, our investigation found no notable effect on the valence band maximum upon doping. The observed red-shift presents a potential advantage for precisely adjusting the absorption edge in tandem solar cells, particularly when specific energy gaps are required.

Impact of photoinduced phase segregation in mixed-halide perovskite absorbers on their material and device stability

Mixed-halide perovskites enable bandgap engineering for tandem solar cell and light-emitting diode applications. However, photoinduced halide phase segregation introduces a compositional instability, that is, formation of I-rich and Br-rich phases, which compromises photovoltaic efficiency and stability. While optical and structural studies of the photoinduced phase segregation in mixed-halide perovskites have been reported, its impact on the material stability is missing. Here, a detailed compositional analysis of mixed-halide perovskite films using x-ray and ultraviolet photoelectron spectroscopy (UPS) was carried out to determine how their stability in various environments depends on the halide ratio. A series of perovskite thin films were fabricated with the composition CH3NH3Pb(IxBr1−x)3, where x = 0.00, 0.25, 0.50, 0.75, and 1.00, and analyzed under different conditions, such as exposure to light in ambient and in nitrogen atmosphere, as well as storage in the dark. From the spectroscopy results, complemented with structural and optical properties, it was found that the deletion of halide ions from the surface is facilitated in mixed-halide perovskites in comparison with pure halide perovskites. A higher stability was found for the mixed-halide perovskite containing less than 25% Br, and it decreases with increasing Br content. This study also established the effect of the Br/I ratio on the energy landscape of the materials. The UPS spectra reveal that photoinduced degradation results in a mismatch of the energy levels at the perovskite/transport layer interface, which may limit the collection of charge carriers. These findings correlate well with the photovoltaic device stability under similar degradation conditions.

Strain Regulation of Mixed-Halide Perovskites Enables High-Performance Wide-Bandgap Photovoltaics.

Wide-bandgap mixed-halogen perovskite materials are widely used as top cells in tandem solar cells. However, serious open-circuit voltage (Voc ) loss restricts the power conversion efficiency (PCE) of wide-bandgap perovskite solar cells (PSCs). Herein, it is shown that the resulting methylammonium vacancies induce lattice distortion in methylammonium chloride-assisted perovskite film, resulting in an inhomogeneous halogen distribution and low Voc . Thus, a lattice strain regulation strategy is reported to fabricate high-performance wide-bandgap PSCs. Rubidium (Rb) cations are introduced to fill the A-site vacancy caused by the methylammonium volatilization, which alleviates shrinkage strain of the perovskite crystal. The reduced lattice distortion and increased halide ion migration barrier result in a homogeneous mixed-halide perovskite film. Due to improved carrier transport and suppressed nonradiative recombination, the Rb-treated wide-bandgap PSC (1.68eV) achieves an excellent PCE of 21.72%, accompanied by a high Voc of 1.22V. The resulting device maintains more than 90% of its initial PCE after 1500h under 1-sun illumination conditions.

Insights into the Growth Orientation and Phase Stability of Chemical-Vapor-Deposited Two-Dimensional Hybrid Halide Perovskite Films.

Chemical vapor deposition (CVD) offers a large-area, scalable, and conformal growth of perovskite thin films without the use of solvents. Low-dimensional organic-inorganic halide perovskites, with alternating layers of organic spacer groups and inorganic perovskite layers, are promising for enhancing the stability of optoelectronic devices. Moreover, their multiple quantum-well structures provide a powerful platform for tuning excitonic physics. In this work, we show that the CVD process is conducive to the growth of 2D hybrid halide perovskite films. Using butylammonium (BA) and phenylethylammonium (PEA) cations, the growth parameters of BA2PbI4 and PEA2PbI4 and mixed halide perovskite films were first optimized. These films are characterized by well-defined grain boundaries and display characteristic absorption and emission features of the 2D quantum wells. X-ray diffraction (XRD) and a noninteger dimensionality model of the absorption spectrum provide insights into the orientation of the crystalline planes. Unlike BA2PbI4, temperature-dependent photoluminescence measurements from PEA2PbI4 show a single excitonic peak throughout the temperature range from 20 to 350 K, highlighting the lack of defect states. These results further corroborate the temperature-dependent synchrotron-based XRD results. Furthermore, the nonlinear optical properties of the CVD-grown perovskite films are investigated, and a high third harmonic generation efficiency is observed.

Anion Confinement for Homogenous Mixed Halide Perovskite Film Growth by Electrospray.

Wide-bandgap perovskites are promising absorbers for state-of-the-art tandem solar cells to feasibly surpass Shockley-Queisser limit with low cost. However, the commonly used mixed halide perovskites suffer from poor stability, particularly, photoinduced phase segregation. Electrospray deposition is developed to bridge the gap of growth rate between iodide and bromide components during film growth by spatially confining the anion diffusion and eliminating the kinetic difference, which universally improves the initial homogeneity of perovskite films regardless of device architectures. It thus promotes the efficiency and stability of corresponding solar cells based on wide-band gap (1.68eV) absorbers. Remarkable power conversion efficiency (PCE) of 21.44% and 20.77% are achieved in 0.08 cm2 and 1.0 cm2 devices, respectively. And these devices maintained 90% of their initial PCE after 1550h of stabilized power output (SPO) tracking upon 1 Sun irradiation (LED) at room temperature. This article is protected by copyright. All rights reserved.

Halide Ion Migration in 2D Metal Halide Perovskites

Two-dimensional (2D) halide perovskites have drawn attention for their unique optoelectronic properties. Interestingly, Ruddlesden-Popper 2D mixed-halide perovskite films with spacer cations such as butylammonium and Dion-Jacobson 2D mixed-halide perovskite films with 1,4-phenylenedimethanammonium undergo halide segregation under irradiation. Anions become mobile under steady state irradiation to form I-rich and Br-rich domains. Upon ceasing illumination, film reverts to their original, mixed-halide compositions, establishing the reversibility of the phase segregation phenomenon. However, if films are in contact with dichloromethane, light irradiation causes the sequential expulsion of iodide and bromide and introduces irreversible changes to 2D films. The sequential disappearance of I- and Br- from pristine films (BA2Pb2Br4, and BA2Pb2I4) under photoirradiation, as observed from variances in expulsion rates, reflect differences in halide ion mobilities in these films. The impact of anion migration, leading to I- and Br- expulsion into solvents, within the context of 2D perovskite photostability will be discussed.

Mixed-Halide Perovskites with Halogen Bond Induced Interlayer Locking Structure for Stable Pure-Red PeLEDs.

Mixed-halide perovskites enable precise spectral tuning across the entire spectral range through composition engineering. However, mixed halide perovskites are susceptible to ion migration under continuous illumination or electric field, which significantly impedes the actual application of perovskite light-emitting diodes (PeLEDs). Here, we demonstrate a novel approach to introduce strong and homogeneous halogen bonds within the quasi-two-dimensional perovskite lattices by means of an interlayer locking structure, which effectively suppresses ion migration by increasing the corresponding activation energy. Various characterizations confirmed that intralattice halogen bonds enhance the stability of quasi-2D mixed-halide perovskite films. Here, we report that the PeLEDs exhibit an impressive 18.3% EQE with pure red emission with CIE color coordinate of (0.67, 0.33) matching Rec. 2100 standards and demonstrate an operational half-life of ∼540 min at an initial luminance of 100 cd m-2, representing one of the most stable mixed-halide pure red PeLEDs reported to date.

Organizing Uniform Phase Distribution in Methylammonium-Free 1.77eV Wide-Bandgap Inverted Perovskite Solar Cells.

Disordered crystallization and poor phase stability of mixed halide perovskite films are still the main factors that compromise the performance of inverted wide bandgap (WBG; 1.77eV) perovskite solar cells (PSCs). Great difficulties are evidenced due to the very different crystallization rates between I- and Br-based perovskite components through DMSO-alone assisted anti-solvent process. Here, a zwitterionic additive strategy is reported for finely regulating the crystal growth of Cs0.2 FA0.8 Pb(I0.6 Br0.4 )3 , thereby obtaining high-performance PSCs. The aminoethanesulfonic acid (AESA) is introduced to form hydrogen bonds and strong PbO bonds with perovskite precursors, realizing the complete coordination with both the organic (FAI) and inorganic (CsI, PbI2 , PbBr2 ) components, balancing their complexation effects, and realizing AESA-guided fast nucleation and retarded crystallization processes. This treatment substantially promotes homogeneous crystal growth of I- and Br-based perovskite components. Besides, this uniformly distributed AESA passivates the defects and inhibits the photo-induced halide segregation effectively. This strategy generates a record efficiency of 19.66%, with a Voc of 1.25V and FF of 83.7% for an MA-free WBG p-i-n device at 1.77eV. The unencapsulated devices display impressive humidity stability at 30±5% RH for 1000h and much improved continuous operation stability at MPP for 300h.

Self‐Tracking Solar Concentrator with Absorption of Diffuse Sunlight

AbstractThe highest solar cell efficiencies are obtained with concentrating systems. However, these systems have two major drawbacks: solar tracking is needed and diffuse sunlight is poorly absorbed. Here, a system that overcomes both limitations is presented, by exploiting light‐induced halide segregation in mixed halide perovskite films. A monolayer of silica microspheres focuses direct sunlight in a mixed halide perovskite film below. Through light‐induced phase segregation a low bandgap region forms in the focal point. Together with funneling of excited states toward the low bandgap regions, this results in a voltage increase characteristic for concentrating systems. Diffuse sunlight is still absorbed by the high bandgap material, avoiding the loss of diffuse sunlight characteristic for conventional concentrators. The formation of low bandgap regions in the perovskite is dynamic, and can follow the position of the focus as the sun moves throughout the day, making solar tracking unnecessary. With detailed optical and electrical simulations, it is shown that this concept can lead to an increase in both voltage and current. This leads to a 6.6% absolute increase in power conversion efficiency compared to the film without microspheres. Absorption and emission measurements confirm the concentration effect, showing the promising potential for a self‐optimizing concentrating system.

Band-gap-engineered mixed-halide perovskite films through vacuum-based deposition approach

Mixed-halide perovskites offer the important characteristic of band-gap tunability, which is essential for tandem solar cells. Herein, the single-source vapor deposition method is reported for MAPbBr2Cl1 (MA (methyl ammonium) = CH3NH3), MAPbBr1.5Cl1.5 and MAPbBr1Cl2 perovskite films utilizing the corresponding mixed-halide perovskite nanoparticles as a source for thermal evaporation. Further, band-gap tuning in vacuum-deposited MAPbBr3 thin films is performed through MACl treatment with successful band-gap tuning from 2.37 to 2.48 eV. The limitation of chlorine (Cl) incorporation into the perovskite structure at room temperature is tackled by MACl treatment of vapor-deposited MAPbBr2Cl1, MAPbBr1.5Cl1.5 and MAPbBr1Cl2 films. The structural properties of MAPbBr3−x Cl x films show a continuous shift in the X-ray diffraction peak toward a higher 2θ value, confirming chlorine incorporation into the perovskite structure. Band-gap tuning in MAPbBr3−x Cl x films, from 2.37 to 2.86 eV, is confirmed by absorption spectroscopy. The mixed-halide perovskite films show an improved microstructure with MACl treatment, as observed from the increased grain size of the films. Further, emission studies show good stability of MAPbBr3−x Cl x films against phase segregation under continuous exposure to 325 nm wavelength illumination of 100 mW/cm2 for more than 60 min. The diminished phase segregation might help in advancing the application of mixed-halide perovskites for reliable optoelectronic devices.

Partial Replacement of Dimethylformamide with Less Toxic Solvents in the Fabrication Process of Mixed-Halide Perovskite Films

The technology of perovskite solar cells (PSC) is getting close to breaching the consumer market. Yet, one of the current challenges is to reduce the toxicity during their fabrication by reducing the use of the toxic solvents involved in the perovskite fabrication process. A good solubilization of lead halides used in hybrid perovskite preparation is required, and it is only possible with polar solvents. A mixture of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) is the most popular solvent combination for a perovskite precursor solution. DMF is necessary to ensure a good dissolution of lead iodide, but it is also the most toxic solvent. In this paper, we study the replacement of the dimethylformamide with presumably less toxic alternatives, such as N-methyl-2-Pyrrolidone (NMP) and ethyl acetate (EA), for the preparation of the K0.1FA0.7MA0.2PbI2.8Cl0.2 (KFAMA) hybrid perovskite. The perovskite thin films were investigated by various characterization techniques: X-ray diffraction, atomic force microscopy, scanning electron microscopy, and UV–vis spectroscopy, while the photovoltaic parameters were determined by measuring the IV curves of the corresponding solar cells. The present study shows that by keeping the same deposition parameters as when only DMF solvent is used, the partial solvent substitution with NMP and EA gives promising results for reducing the toxicity of the fabrication process of KFAMA-based PSCs. Thus, with no specific optimization of the deposition process, and for the maximum possible partial substitution of DMF with NMP and EA solvents, the loss in the power conversion efficiency (PCE) value is only 35% and 18%, respectively, associated with the more structural defects promoted by NMP and EA.

Mitigating lattice strain and phase segregation of mixed-halide perovskite films via dual chloride additive strategy toward highly efficient and stable perovskite solar cells

Mixed halide perovskites could be used to fabricate the high-efficient single junction perovskite solar cells (PSCs) and also be assembled into the tandem solar cells. However, those perovskites always suffered from microstrain and phase segregation issues, which tend to bring in extra non-radiative recombinations and aggravate the energy losses and degradation of PSCs. Here, we developed a dual chloride additive strategy to overcome these issues. Compared with the pristine and single additive films, the perovskite films with dual chloride additive possessed the lowest microstrain and the least defects, and thus the activation energy related to phase segregation of those films was improved from 40.21 kJ mol−1 to 59.08 kJ mol−1. Density functional theory revealed that the iodide ion migration also had been inhibited by the dual chloride additive as the energy barrier increased from 0.41 eV to 0.57 eV. PSCs with dual chloride additive showed a efficiency of 22.94%, higher than that of the pristine PSCs (20.62%) and the single additive PSCs. Moreover, the unencapsulated PSCs with dual chloride additive exhibited better working stability maintained 93% of their original efficiency after 1000 s of MPP tracking operation in ambient air, while their counterpart PSCs maintains 46%.

Multifunctional l-tryptophan derivative induced surface passivation for lateral perovskite photodetectors

Organic-inorganic hybrid perovskites have already been employed as promising light-sensitive materials for high-performance photodetectors (PDs) due to their intriguing optoelectronic features. Nonetheless, such perovskite-based PDs often suffer from low sensitivity, high dark current and inevitable degradation. In this work, a novel multifunctional molecule l-tryptophan ethyl ester hydrochloride (l-TEEH) was used to treat the surface defects of triple-cation mixed halide perovskite film. It is found that the modulator with multiple functional groups can effectively passivate the uncoordinated ions (Pb2+ and I-) and halide (I and Cl) vacancies of the perovskite film. Owing to the reduced defects, the dark current of the pristine perovskite PD significantly decreases from ∼ 10-9 A to ∼ 10-11 A after the l-TEEH treatment. Moreover, the perovskite PD with the l-TEEH treatment exhibits a large photoresponsivity (1.27 A/W) and an ultrahigh on/off ratio (∼9 × 103). More impressively, the optimized device shows excellent stability in air with a relative humidity of 40–50 %. Furthermore, the reliable imaging capability of perovskite device with the l-TEEH treatment is also successfully demonstrated.

Flexible, stable, and self-powered photodetectors embedded with chemical vapor deposited lead-free bismuth mixed halide perovskite films

The emerging revolution in the field of Internet of Things (IoT) necessitates the development of flexible, self-powered, and cost-effective photodetectors such as metal halide-based perovskite photodetectors. Lead-free ternary metal halides have emerged as a promising option having no technical barrier with regard to toxicity. However, the performance metrics of lead-free ternary metal-halide-based optoelectronic devices lags behind those of conventional lead-halide-based devices. In this study, we demonstrate that chemical-vapor-deposited methylammonium bismuth iodide (MA3Bi2I9 (MBI)) films and their mixed halide analogues (MA3Bi2I6Br3 (MBIB)) and MA3Bi2I6Cl3 (MBIC)) enhance the performance metrics and stability of photodetectors by enabling the growth of films with smooth and compact morphology. MBIC-integrated devices achieved a responsivity of ∼ 0.92 A/W and specific detectivity of ∼ 2.9 × 1013 Jones under no bias and UV (382 nm) illumination, which is approximately-three times higher than MBI counterparts. They also exhibit outstanding operational stability by maintaining 94 % of the photoresponse after illumination for 500 h (382 nm wavelength at light intensity of 1.0 mW/cm2) in ambient air. Furthermore, these devices show satisfactory mechanical stability, with the attenuation being as low as 15 % of initial photoresponse after bending for 5,000 cycles at 5 % tensile strain. Our findings indicate that MBIC film-integrated devices have immense potential in optoelectronics.

An amino-phthalocyanine additive enhances the efficiency of perovskite solar cells through defect passivation in mixed-halide films

Although perovskite solar cells (PSCs) can be easy to process and display exceptional optoelectronic properties, the presence of defects and poor control over crystallization can adversely affect their efficiency and long-term stability. In this study, we employed iron(II)-2,9,16,23-tetraamino-phthalocyanine (FeTAP) as a small-molecule additive capable of defect passivation in a mixed-halide perovskite (MHP). In particular, we used an additive engineering treatment protocol to introduce FeTAP into the MHP layer to significantly suppress perovskite defects, improve charge extraction, and inhibit perovskite degradation. A PSC incorporating a FeTAP-modified perovskite layer exhibited a power conversion efficiency (PCE) of 18.81% and retained 72.5% of its initial PCE after storage for 30 days. Thus, adding FeTAP to the MHP film significantly enhanced the efficiency and stability of the resulting PSC. Iron(II)-2,9,16,23-tetraamino-phthalocyanine (FeTAP), when used as a small-molecule additive in the precursor solution of a mixed-halide perovskite, enhances the photovoltaic properties of resulting planar perovskite solar cells. • We have added iron(II)-2,9,16,23-tetraamino-phthalocyanine (FeTAP), a small molecule capable of interacting with a mixed-halide perovskite (MHP), during the fabrication of n–i–p PSCs. The power conversion efficiencies were improved for our tested PSCs incorporating FeTAP. • The morphologies of the mixed-halide perovskite films prepared with the small-molecule additive FeTAP were superior to that of the pristine control perovskite film, suggesting that the FeTAP units interacted with undercoordinated Pb 2+ ions within the films, leading to higher-performance PSCs. • Incorporating the additive in the perovskite precursor solution resulted in perovskite films of superior film quality and with lower numbers of defects, thereby enhancing the photovoltaic performance of resulting PSCs and providing higher power conversion efficiencies.

Perovskite Plasticity: Exploiting Instability for Self‐Optimized Performance

AbstractHalide perovskites display outstanding photoluminescence quantum yield, tunable emission, and simple deposition, which make them attractive for optoelectronics. At the same time, their facile ion migration and transformation under optical, electrical, and chemical stress are seen as a major limitation. Mixed halide perovskites are particularly problematic since optical excitation can cause changes in the bandgap that are detrimental for solar cell and light‐emitting diode efficiency and stability. In this work, instead of preventing such changes, photo‐induced halide segregation in perovskites is exploited to enable responsive, reconfigurable, and self‐optimizing materials. The mixed halide perovskite film is trained to give directional light emission using a nanophotonic microlens; through a self‐optimized process of halide photosegregation, the system mimics the training stimulus. Longer training leads to more highly directional emission, while different halide migration kinetics in the light (fast training) and dark (slow forgetting) allows for material memory. This self‐optimized material performs significantly better than lithographically aligned quantum dots because it eliminates lens‐emitter misalignment and automatically corrects for lens aberrations. The system shows a combination of mimicking, improving over time, and memory, which comprise the basic requirements for learning, and allow for the intriguing prospect of intelligent optoelectronic materials.

Improving inorganic perovskite photovoltaic performance via organic cation addition for efficient solar energy utilization

Organic cations help in executing better crystal growth of halide perovskites. Herein, we have realized improved all-inorganic cesium lead halide perovskite film quality with reduced pinholes and high crystallinity in phenylethylammonium (PEA+) assisted perovskite. Additionally, PEA+ cation acts as an additive to control intermediate perovskite phase and executes pure phase perovskite crystal growth as compared to MA+ and FA+ cations assisted perovskite films. X-ray photoelectron and UV–vis spectroscopy results revealed that adding PEA+ in the perovskite helps in almost uniform distribution of Br− ion after post-annealing process. Furthermore, depth profiling analysis reveals that PEA+ in the intermediate phase perovskite interacts more with the ZnO layer beneath perovskite, which helps in the fabrication of compact film. PEA+ sublimates after post-annealing treatment of 300 °C, as no evidence of PEA+ existence was found in characterizations for post-annealed perovskite films. This brings multiple benefits to inorganic mixed halide perovskite film formation. The best performing perovskite solar cell (PSC) exhibits a high conversion efficiency of 14.75% as well as enhanced stability of maintaining almost 83% of its initial efficiency for 400 h. Electrochemical impedance spectroscopy and space-charge-limited current results suggests reduced recombination loss and defect densities in PEA+ assisted PSC.

Hole Trapping in Halide Perovskites Induces Phase Segregation

ConspectusMetal halide perovskites have garnered a great deal of attention for their applications in photovoltaics, LEDs, and radiation detection. The ease of solution processing high-quality perovskite semiconductors with large absorption coefficients and tolerance to native defects is decidedly attractive. Additionally, the ability to precisely tune the band gap of halide perovskites through compositional alloying of the halide ion is of particular interest for a range of applications, especially for tandem solar cells. However, under steady state light irradiation, an initially homogeneous mixed halide perovskite (MHP) will form local domains that are rich in one halide ion (e.g., Br or I). This light-induced phase segregation in MHPs forms iodide-rich domains that act as charge carrier traps and lowers the efficiency of perovskite-based devices. Thus, phase segregation poses a serious challenge to the implementation of MHPs in real-world device settings. Interestingly, when a phase segregated MHP film is placed in the dark, entropic driving forces become dominant and the segregated perovskite remixes and returns to its initially homogeneous state. Several key mechanistic details of phase segregation have been elucidated over the years. However, there are still aspects of halide segregation that are not clear, and there is ongoing debate in the literature as to what are the key factors that contribute to the mechanism.This Account discusses recent results that point to the specific role of hole trapping in phase segregation. Interestingly, generation of holes through above-band-gap excitation or through electrochemical injection increases ion migration and leads to phase segregation. The thermodynamic and redox properties of halide perovskites provide a strong driving force for hole trapping and oxidation of iodide species in MHPs. However, mobile halide species within the perovskite lattice take time to migrate and generate halide-rich domains. When in contact with a nonpolar solvent, the migration of iodine species is further extended to expulsion of iodine from the perovskite film. Thus, the mobility of halides and their susceptibility to hole-induced oxidation play a crucial role in determining the long-term stability of metal halide perovskites. Strategies to gain kinetic control over ion migration to slow phase segregation are needed to overcome these hurdles and achieve stable mixed halide perovskites. Modification of the perovskite composition through introduction of different cations or halide ions, or introduction of low-dimensional perovskite phases may suppress phase segregation. Thus, in achieving stability and improving the efficiency of perovskite solar cells and light emitting devices with minimal impacts, suppression of segregation remains the key factor.

Mixed halide head perovskites thin films: Stability and growth investigation

Herein, we investigate the mixed halide perovskite films with the formula MAPbX3 where (X3 = Br3, Cl3, I3, Br2Cl, Br2I, and I2Cl) prepared by Spin-Coating in order to study the effects of partial and total substitution of Br. For this purpose, we have carried out a series of characterization techniques, including x-ray diffraction (XRD), Scanning electron microscopy (SEM), UV–visible spectroscopic; we find that all films content with partial Bromide exhibit two peaks located at 2θ angles of 14,94° and 30,2° matching to crystallographic planes (110) and (220) respectively correspond to perovskite structure, in the case of MAPbCl3, MAPbI3 or mixed MAPbI2Cl the characteristics peaks (110) and (220) were identified at 2θ angles of 14,16° and 28,53° respectively. The surface morphology of the different mixed lead halides films was examined by SEM, MAPbBr2I has the highest crystallinity and grain size. Furthermore, All the mixed halide films exhibited strong absorbance with bandgap values ranging between 1.5 eV and 2.5 eV. Moreover, we investigated the crystal structure, morphology, and color change of MAPbX3 after four weeks under dark with 22% humidity; the Bromide-doped samples demonstrate a higher degree of stability based on the study of their degradation mechanisms.