Inverse Temperature Crystallization Research Articles

Anisotropic optoelectronic properties of lead-free Cs3Bi2I9 single-crystal photodetectors

Lead-free halide perovskites have attracted widespread research interest due to their excellent optoelectronic properties and environmental friendliness. As one of the bismuth iodide compounds, Cs3Bi2I9 perovskite has been extensively explored in the field of photovoltaic devices and radiation detectors due to their non-toxic lead-free components and excellent stability. In this work, we successfully grow large-sized Cs3Bi2I9 single crystals (SC) with (l00) and (00l) crystal exposure facets by inverse temperature crystallization method. Under 525 nm light illumination with the intensity 15 mW cm−2 and 7 V bias, the (l00) Cs3Bi2I9 SC shows 2 times higher photocurrent, 3.6 times higher responsivity, and 2.8 times higher detectivity than the (00l) Cs3Bi2I9 SC, respectively. Superior response time in the scale of millisecond is obtained in both (l00) and (00l) Cs3Bi2I9 SCs. Based on the first-principle calculation, the (l00) SC possesses a higher charge distribution density and a wider dispersion distribution than (00l) SC, suggesting that more electrons in the (l00) SC can be excited in a wider range. The tighter arrangement of Cs+ and [BiI6]− octahedra in the (l00) SC than (00l) SC leads to the anisotropic photoelectric performance in (l00) and (00l) Cs3Bi2I9 SCs. Our results provide a strategy for the oriental growth of Cs3Bi2I9 SCs and the design of anisotropic optoelectronic devices with excellent performance.

Analysis on the defect states of FAxMA1−xPbI3 perovskite single crystals grown by inverse-temperature crystallization

Analysis on the defect states of FAxMA1−xPbI3 perovskite single crystals grown by inverse-temperature crystallization

Development of high-performance ultrafast photodetector using CsPbBr3 perovskite single crystal

Here, we have developed a high-performance photodetector with enhanced photoelectric conversion efficiency and rapid response kinetics using an inorganic CsPbBr3 perovskite single crystal (PSC). A large area of high-quality PSC has been synthesized using a novel modified inverse temperature crystallization (ITC) process. The formation of the single crystal of the CsPbBr3 perovskite in an orthorhombic phase was confirmed by the X-ray diffraction (XRD) spectra while the excellent light absorption characteristics are corroborated with UV-Vis studies. A proposed Metal-Semiconductor-Metal (M-S-M) photodetector device structure using the CsPbBr3 PSC (Au/CsPbBr3/Au) has been examined by using monochromatic light in a wavelength range of 350–700 nm. The PSC photodetector exhibits excellent spectral responsivity of ∼ 0.42 A/W, detectivity of 6.26 × 1010 Jones, and external quantum efficiency of ∼ 95% with an ultrafast response/recovery time of ∼ 40/35 ms. Such excellent results unveil a new perspective in the PSC-based next-generation optoelectronic devices.

Fast and Facile Synthesis of Passivated Perovskite Single Crystals with Zn-Porphyrin Derivatives

Organic-inorganic trihalide, ABX3 perovskite are excellent candidates for advanced optoelectronic applications beyond photovoltaics. Perovskite single crystals offer several advantageous special features, such as a long diffusion length, low trapped carrier density, and outstanding environmental stability to use in optoelectronics. In this work, Zn has been incorporated into MAPbBr3 single crystals as Zn- Porphyrin to passivate the bulk crystals and enhance their optical and electrical properties. The inverse temperature crystallization phenomenon was used to crystallize MAPbBr3 rapidly in hot solutions. The structural and optical characterization confirms that the passivation enhanced the optoelectronic properties of the single crystals.

Competing formation of α and δ-FAPbI3 in perovskite ink using 2-methoxyethanol as the solvent

2-Methoxyethanol (2-Me) is a promising solvent for large-area perovskite film preparation. Understanding the competing processes of α and δ-FAPbI3 in 2-Me is crucial for advancing the application of 2-Me in FAPbI3 film coating. In this study, FAPbI3 microcrystals are fabricated by inverse temperature crystallization method at 100 °C, and are used as a platform to investigate the competing formation of α and δ-FAPbI3 in 2-Me. Perovskite inks are analyzed using Raman, FTIR and DLS, and it is found that cluster ratio is closely related to the kinetic formation of δ-FAPbI3. The formation of α-FAPbI3 can be significantly promoted when clusters are dissociated with additives (excess FAI or I2). These findings provide valuable insights into the influence of precursor inks on perovskite phases.

Passivation of defective states in single crystal MAPbBr3 and their optoelectronic properties study

We fabricated high-quality Methylpropyl lead bromide (MAPbBr3) single crystals (SC) by introducing moderate amount electron-rich amino-terminated polyoxypropylene (PEA) additives via inverse temperature crystallization (ITC) method. The intramolecular vibrations and defective states of prepared MAPbBr3 single crystals were systemically studied by the in situ variable-temperature Fourier Transform Infrared (FTIR), X-ray photoelectron spectroscopy (XPS), the synchrotron-based X-ray absorption near edge structure (XANES) et al. We find the proper amount PEA additives would prevent the formation of intermediate states and crystal boundaries, passivating the density of defective states. The X-ray detection properties of single-crystal MAPbBr3 crystals were investigated, using both high dose and low dose X-ray photons at 40 keV in synchrotron beamlines. The photocurrent of optimized PEA-treated MAPbBr3 single crystals demonstrate better performance compared with the as-prepared single crystals. Meanwhile, the decay time of MAPbBr3 single crystal is decreased from 376 ns to 17.1 ns by Time-resolved photoluminescence (TRPL) decay measurement, owing to the defect passivation by 0.5 wt% PEA additives. The PEA-treated single crystals possess much faster decay time than the commercialized Cerium-doped Yttrium Aluminum Garnet (Ce:YAG) scintillator (∼100ns). These results help elucidate the passivation of defective states and contribute paths to manufacture high-quality single crystal perovskites for next-generation optoelectronic devices.

Spectrally Stable Deep-Blue Light-Emitting Diodes Based on Layer-Transferred Single-Crystalline Ruddlesden-Popper Halide Perovskites.

A novel approach to producing high-color-purity blue-light-emitting diodes based on single-crystalline Ruddlesden-Popper perovskites (RPPs) is reported. The utilization of a pure bromide composition eliminates any possibility of halide segregation, which can otherwise lead to undesired shifts in the emission wavelength or irreversible degradation of the spectral line width. Phase-pure PEA2MAPb2Br7 single crystals with a lateral size exceeding 1 cm2 can be synthesized using the inverse temperature crystallization method. To prepare RPP layers with a thickness of less than 50 nm, we employ a thinning process of the initially thick bulk crystals, followed by a dry-transfer process to place them onto a hole transport layer and an indium-tin-oxide-coated glass substrate. By utilizing polydimethylsiloxane as a handling layer, deformations of the bulk RPP crystal and exfoliated RPP layer, as well as the formation of defects such as pinholes, can be effectively suppressed. Subsequent depositions of an electron transport layer and a metal contact complete the fabrication of electroluminescence (EL) devices. The EL devices utilizing the single-crystalline RPP demonstrate excellent spectral stability across a broad range of the applied bias voltage spanning from 4.5 to 10 V, exhibiting a significantly narrow line width of 14 nm at an emission wavelength of 440 nm that can potentially cover 99.3% of the Rec. 2020 color gamut. The sharp EL emission spectrum can be effectively preserved, avoiding any broadening of the line width, by suppressing Joule heating throughout the device operation, in addition to the intrinsic stability of single-crystalline RPPs.

Ionic liquid-assisted growth of high-quality methylammonium lead bromide single crystals for photodetection applications

The addition of a 1-butyl-3-methylimidazolium bromide (BMIB) ionic liquid to the MAPbBr3 precursor solution shows a significant influence on the crystal optoelectronic properties and photodetection performance.

Growth methods' effect on the physical characteristics of CsPbBr3 single crystal.

This study offers an extensive exploration into approaches for cultivating CsPbBr3 SCs using inverse temperature crystallization (ITC), with a specific focus on seed-induced (method (1)) and nucleation-mediated (method (2)) growth techniques. Our findings reveal that leveraging seed-assisted growth at lower temperatures yields noteworthy enhancements in the material's optical and electrical behaviors, outperforming the outcomes achieved through nucleation-driven growth. Concretely, through the employment of the space charge limited current (SCLC) technique, an evident contrast emerges in the trap-populated threshold voltage between the seed-facilitated crystal (SC1) (measuring 0.309 V) and its nucleation-facilitated counterpart (SC2) (measuring 1.513 V), consequently giving rise to discernable dissimilarities in trap density assessments. Evidence from temperature-dependent analysis of space charge limited currents substantiates these findings, revealing trap density values of 8.81 × 109 cm-3 for SC1, juxtaposed with 2.08 × 1010 cm-3 for SC2. Additionally, the SC1 displays a notably diminished trap energy level. Furthermore, the investigation underscores the affirmative influence of method (1) at lower temperatures on the optical and crystalline characteristics of the substance. This effect is evidenced by enhanced photoluminescence (PL) reactions and reduced lattice strain (Ls), as determined through X-ray diffraction (XRD) techniques. Moreover, the research establishes the substantial impact of this enhanced crystallization technique on the photodetector (PD) attributes of the crystal. This effect induces elevated levels of detectivity and responsivity for method (1).

Solution-processed lead-free cesium titanium halide perovskites and their structural and optical characteristics

Two primary challenges impede the extensive utilization of organic-inorganic lead halide perovskites: instability and potential risk of lead contamination. This paper describes an easy and effective solution-phase method for synthesizing lead-free Cs2TiI6 perovskites using inverse temperature crystallization. The perovskite precursor was deposited on glass substrates using various methods. The Cs2TiI6 films exhibit a cubic structure with a lattice parameter of 11.57 Å. The drop-cast thin film exhibited strong and broad absorption in the visible spectrum, indicating that Cs2TiI6 possesses notable optical properties. The optical energy gap calculated for both direct and indirect is 1.68 eV and 1.65 eV, respectively). The refractive index and optical conductivity demonstrate that Cs2TiI6 is an excellent optical absorber for photodevices. This study offers valuable perspectives for the advancement of lead-free double perovskites.

Exploring the synthesis, structure, and optoelectronic properties of lead-free halide perovskite Cs3Bi2I9 in single crystal and polycrystalline forms

In recent years, caesium bismuth iodide (Cs3Bi2I9), a lead (Pb)-free halide perovskite, has drawn more attention as a potential material than traditional semiconductor materials due to its lack of Pb toxicity and its outstanding stability against atmospheric air and moisture. Herein, the inverse temperature crystallization method is adopted to grow high-quality hexagonal-phase Cs3Bi2I9 perovskite single crystals. Furthermore, a Cs3Bi2I9 perovskite thin film is fabricated by a solution process using the two-step spin coating technique. A collective analysis of the structural properties, surface morphology, thermal stability, phase transition, and optoelectronic properties of these single crystal and polycrystalline thin films provides a comprehensive understanding and design strategy to develop environmentally stable, Pb-free, and high-performance photovoltaic and optoelectronic devices based on Cs3Bi2I9 perovskite. The findings of this study contribute to the advancement of perovskite-based technologies and pave the way for their successful integration into the renewable energy and optoelectronics industries.

Phase transformations and vibrational properties of hybrid organic–inorganic perovskite MAPbI3 bulk at high pressure

The structural stability and internal properties of hybrid organic–inorganic perovskites (HOIPs) have been widely investigated over the past few years. The interplay between organic cations and inorganic framework is one of the prominent features. Herein we report the evolution of Raman modes under pressure in the hybrid organic–inorganic perovskite MAPbI_3 by combining the experimental approach with the first-principles calculations. A bulk MAPbI_3 single crystal was synthesized via inverse temperature crystallization (ITC) technique and characterized by Raman spectroscopy, while the diamond anvil cells (DACs) was employed to compress the sample. The classification and behaviours of their Raman modes are presented. At ambient pressure, the vibrations of inorganic PbI_6 octahedra and organic MA dominate at a low-frequency range (60–760 cm^{-1}) and a fingerprint range (900–1500 cm^{-1}), respectively. The applied pressure exhibits two significant changes in the Raman spectrum and indicates of phase transition. The results obtained from both experiment and calculations of the second phase at 3.26 GPa reveal that the internal vibration intensity of the PbI_6 octahedra (< 110 cm^{-1}) reduces as absences of MA libration (150–270 cm^{-1}) and internal vibration of MA (450–750 cm^{-1}). Furthermore, the hydrogen interactions around 1300 cm^{-1} remain strong high pressure up to 5.34 GPa.

Double buffer of MAPbBr3 QDs using a bulk crystal source by the LARP method and MABr modifier for CsPbBr3 perovskite light-emitting diodes

In this work, we employed MAPbBr3 quantum dots (QDs) and MABr salt as buffer layers to boost the optoelectronic characteristics of CsPbBr3 perovskite light-emitting diodes (PeLEDs). The MAPbBr3 QDs were prepared by ligand-assisted reprecipitation method and using MAPbBr3 bulk single crystals as source material, but traditional powder source. The MAPbBr3 bulk single crystals were obtained by inverse temperature crystallization method. The purification cycles of bulk-crystal source MAPbBr3 quantum dots (bc-MAPbBr3 QDs) were studied. The bc-MAPbBr3 QDs and MABr salt were applied into the PeLED structures. The best brightness reached 7555 cd m−2, and the external quantum efficiency reached 0.318%.

Nucleation-mediated growth of chiral 3D organic-inorganic perovskite single crystals.

Although their zero- to two-dimensional counterparts are well known, three-dimensional chiral hybrid organic-inorganic perovskite single crystals have remained difficult because they contain no chiral components and their crystal phases belong to centrosymmetric achiral point groups. Here we report a general approach to grow single-crystalline 3D lead halide perovskites with chiroptical activity. Taking MAPbBr3 (MA, methylammonium) perovskite as a representative example, whereas achiral MAPbBr3 crystallized from precursors in solution by inverse temperature crystallization method, the addition of micro- or nanoparticles as nucleating agents promoted the formation of chiral crystals under a near equilibrium state. Experimental characterization supported by calculations showed that the chirality of the 3D APbX3 (where A is an ammonium ion and X is Cl, Br or mixed Cl-Br or Br-I) perovskites arises from chiral patterns of the A-site cations and their interaction with the [PbX6]4- octahedra in the perovskite structure. The chiral structure obeys the lowest-energy principle and thereby thermodynamically stable. The chiral 3D hybrid organic-inorganic perovskites served in a circularly polarized light photodetector prototype successfully.

Structural and optical properties of vacancy-ordered double halide perovskites, Cs2TiI6 films

Vacancy-ordered double halide perovskites (DHP) structures have received considerable attention in photovoltaics due to their role in overcoming the lead toxicity issue for conventional halide perovskites. These materials also have tunable bandgaps and excellent optoelectronic properties suitable for a wide range of applications. Herein, we report the synthesis of titanium-based vacancy-ordered DHP, Cs2TiI6 using the Inverse Temperature Crystallization method for the first time. The Cs2TiI6 film's formation, structural and optical properties were also discussed. The films have a single-phase cubic structure with a space group of Fm3¯m (225) and a lattice parameter of 11.55 Å. The crystallite size, dislocation density, and micro-strain of Cs2TiI6 film calculated at (222) plane is 22 nm, 2.5 × 10−3 nm−2, and 0.53 × 10−3, respectively. Optical analysis reveals that Cs2TiI6 exhibits strong and wide optical absorption in the visible spectrum, with direct and indirect band gaps of 1.56 eV and 1.58 eV, respectively. The VESTA-calculated tolerance factor of 0.98 indicates excellent structural stability. These Titanium-based perovskites exhibit promising optoelectronic properties, opening the door for non-toxic perovskite devices with high performance and stability.

Low-Cost Fabrication of Efficient Perovskite Photovoltaics Using Low-Purity Lead Iodide via Powder Engineering

Low cost is the eternal theme for any commercial production. Numerous efforts have been explored to realize low-cost, high-efficiency perovskite solar cells (PSCs), such as replacing the traditional spin-coating method with an economical printing strategy, simplifying the device structure, reducing the number of functional layers, etc. However, there are few reports on the use of low-cost precursors. Herein, we enable the low-cost fabrication of efficient PSCs based on a very cheaper low-purity PbI2 via powder engineering. The low-purity PbI2 is blended with formamidinium iodide followed by dissolving in a 2-methoxyethanol solvent, and then, the high-quality FAPbI3 powders are formed via an inverse temperature crystallization process and solvent washing after several simple processes to reduce the impurities. As a result, the devices fabricated using the as-synthesized black powders based on the low-purity PbI2 exhibit a champion power conversion efficiency (PCE) of 23.9% and retained ∼95% of the initial PCE after ∼400 h of storage in the conditions of 25 ± 5 °C and 25 ± 5 RH% without encapsulation. In addition, the upscaling fabrication of a 5 cm × 5 cm solar minimodule also demonstrates an impressive efficiency of 19.5%. Our findings demonstrate an economic strategy for the commercialization of PSCs from the perspective of low-cost production.

Iodine doping of CsPbBr3: toward highly stable and clean perovskite single crystals for optoelectronic applications

ABSTRACT Caesium-based mixed halide perovskite single crystals, CsPbBr3-xIx, are shown to be good candidates for many optoelectronic applications under ambient conditions. The partial substitution of iodine into the bromine sites of CsPbBr3 single crystal makes attractive effects in optical and structural properties as well as their thermal and phase stability. Herein, the Inverse Temperature Crystallization (ITC) method has been utilised to grow high-quality, large, and single-phase single crystals of CsPbBr2.4I0.6 perovskites. The iodine doping is found to result in improved purity, thermal, phase, and atmospheric stability of the single crystal and helped to tune the band gap. Further, there is a conspicuous decrease in the defect density with iodine doping. Thus the present study establishes iodine doping as a facile route to grow CsPbBr3 single crystals with overall stability and improved defect density with a broad absorption spectrum, that point toward extended optoelectronic and photovoltaic applications.

Modulation of photoluminescence intensity by surface defects of MAPbBr3 crystals

MAPbBr3 single crystals have attracted much attention because of their high quantum efficiency and photoluminescence (PL) peaks. It has been researched that the crystal has two PL peaks and the additional PL peak comes from the “PbBr2” defect in the crystal. This can be well applied to dual-wavelength lasers. However, the change rule of the PL two peaks intensity is not clear. Herein. Crystals with two PL peaks are obtained by inverse temperature crystallization. We research the crystal structures of MABr and PbBr2 in different proportions, and find that these crystals have varying degrees of defects. Moreover, we confirm that these defects are Schottky defects based on experimental and simulated XRD. The optical properties of the samples are studied, which suggest that the PL intensity is related to the ratio of MABr to PbBr2. The energy level distribution of the crystal is calculated by energy level simulation, which further explains that the 536 nm is generated by “PbBr2” and the 567 nm is generated by MAPbBr3. All the results illustrate that the intensity of two peaks can be adjusted by the ratio of MABr to PbBr2. The maximum intensity is at 536 nm for MABr: PbBr2= 2 and 567 nm for MABr: PbBr2= 0.5. We explain this change rule of two peaks intensities from the energy level point of view and obtained MAPbBr3 crystals with high PL intensity corresponding to different wavelengths. This research provides a theoretical basis for the change in PL bimodal intensity, and an experimental reference for perovskite dual-wavelength laser.

MAPb(Br1–xClx)3 Hybrid Perovskite Materials for Direct X-ray Detection

The study and development in recent years of hybrid (organic–inorganic) halide perovskite materials have given them an unprecedented opportunity for direct ionizing radiation detection, given their large attenuation coefficient and sufficient charge carrier mobility lifetime product. The use of single crystals, considered as model materials, allows us to investigate their intrinsic properties. Characterizations under X-ray illumination of detector devices based on methylammonium lead tribromide (MAPbBr3) single crystals, obtained by optimized growths, show good sensitivity but high dark current density. To improve this critical parameter, while using MAPbBr3 as the base material, we employ anion engineering within the halide elements. We present here mixed halide perovskite crystals, with bromide partially replaced with chloride, obtained through optimized growths using modified inverse temperature crystallization in dimethylformamide, leading to high-quality single crystals of the general formula MAPb(Br1–xClx)3. Six chlorine contents are targeted and carefully determined experimentally via energy-dispersive X-ray analysis and X-ray powder diffraction. For each composition, several crystals are synthesized and used to prepare X-ray detection devices. Their optoelectronic properties are determined under standard X-ray medical conditions and hint at the existence of an optimal composition. MAPb(Br0.85Cl0.15)3 exhibits the best sensitivity with a value of S ≈ 3 μC mGyair–1 cm–2 for RQA5 spectral quality and the lowest dark current density with a value of Jdark ≈ 22 nA mm–2, both recorded at a 50 V mm–1 electric field. This sensitivity value doubles our own MAPbBr3 single crystal device and is higher than that of CsI(Tl)- or a-Se-based flat panels. The present work broadens the benefits and drawbacks of employing halide engineering in perovskite materials to improve the optoelectronic performance under high-energy radiation.

Centimeter-sized Cs3Cu2I5 single crystals grown by oleic acid assisted inverse temperature crystallization strategy and their films for high-quality X-ray imaging

Low-dimensional halide perovskites have become the most promising candidates for X-ray imaging, yet the issues of the poor chemical stability of hybrid halide perovskite, the high poisonousness of lead halides and the relatively low detectivity of the lead-free halide perovskites which seriously restrain its commercialization. Here, we developed a solution inverse temperature crystal growth (ITCG) method to bring-up high quality Cs3Cu2I5 crystals with large size of centimeter order, in which the oleic acid (OA) is introduced as an antioxidative ligand to inhibit the oxidation of cuprous ions effieiently, as well as to decelerate the crystallization rate remarkalby. Based on these fine crystals, the vapor deposition technique is empolyed to prepare high quality Cs3Cu2I5 films for efficient X-ray imaging. Smooth surface morphology, high light yields and short decay time endow the Cs3Cu2I5 films with strong radioluminescence, high resolution (12 lp/mm), low detection limits (53 nGyair/s) and desirable stability. Subsequently, the Cs3Cu2I5 films have been applied to the practical radiography which exhibit superior X-ray imaging performance. Our work provides a paradigm to fabricate nonpoisonous and chemically stable inorganic halide perovskite for X-ray imaging.