Pure PbI2 Research Articles

Low-cost and facile synthesis of chromium doped PbI2 nanostructures for optoelectronic devices and radiation detectors: Comparative study

The synthesis of pure and different concentrations of Cr-doped (1, 2.5, 5, 7, 10 wt%) lead iodide (PbI2) nanosheets was successfully achieved using a low-cost and simple microwave method. The prepared Cr-doped PbI2 nanostructures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-Raman, diffuse reflectance, dielectric, and gamma absorption analysis. The structural investigation confirmed the hexagonal phase of the proposed nanostructures without the impurity phase. Morphological studies proved that the undoped PbI2 nanosheet has a size of less than 100 nm, and the size of the prepared Cr-doped PbI2 samples was around 50-60 nm. FT-Raman and optical analysis investigated the doping effects on the pure PbI2 matrix through the slight shifting of characteristics peaks and the energy bandgaps’ variations. The optical bandgap values of pure PbI2 and Cr-doped PbI2 samples were estimated to be ranged from 2.0 eV to 2.2 eV. The obtained values of the dielectric constant were increased from 20 to 27 due to introducing the Cr- ions into the host PbI2 matrix. Together with Cr- dopants, the linear coefficient of Gamma absorption illustrates improvements. To conclude, due to the enhancement in structural morphology, optical, and radiation properties of the synthesized Cr-doped PbI2 nanostructures, those proposed nanosheets potentially are remarkable candidates for various applications including optoelectronics and radiation detectors.

Effects of the PbBr2:PbI2 Molar Ratio on the Formation of Lead Halide Thin Films, and the Ratio's Application for High Performance and Wide Bandgap Solar Cells.

We investigate the effects of the molar ratio (x) of PbBr2 on the phases, microstructure, surface morphology, optical properties, and structural defects of mixed lead halides PbI2(1−x)Br2x for use in solar cell devices. Results indicate that as x increased to 0.3, the surface morphology continued to improve, accompanied by the growth of PbI2 grains. This resulted in lead halide films with a very smooth and continuous morphology, including large grains when the film was formed at x = 0.3. In addition, the microstructure changed from (001)-oriented pure PbI2 to a highly (001)-oriented β (PbI2-rich) phase. The plausible mechanism for the enhanced morphology of the lead halide films by the addition of PbBr2 is proposed based on the growth of a Br-saturated lead iodide solid solution. Furthermore, iodine vacancies, identified by X-ray photoelectron spectroscopy, decreased as the ratio of PbBr2 increased. Finally, an electrical analysis of the solar cells was performed by using a PN heterojunction model, revealing that structural defects, such as iodine vacancies and grain boundaries, are the main contributors to the degradation of the performance of pure PbI2-based solar cells (including high leakage, low stability, and high hysteresis), which was significantly improved by the addition of PbBr2. The solar cell fabricated at x = 0.3 in air showed excellent stability and performance. The device lost merely 20% of the initial efficiency of 4.11% after 1500 h without encapsulation. This may be due to the dense microstructure and the reduced structural defects of lead halides formed at x = 0.3.

Bendable 3D-structured x-ray photodetectors based on pure PbI2 single crystal

PbI2 crystal is a typical layered material with a I–Pb–I monolayer as a repeating unit. Benefiting from the coexistence of ionic and van der Waals bonding, the crystal exhibits low hardness and a low Young’s modulus, slips easily along the a–b plane, and is endowed with inherently high flexibility. In this work, bendable three-dimensional (3D)-structured x-ray photodetectors based on PbI2 crystal were prepared, and finite element simulation was employed to reveal the von Mises stress distribution from the surface to the bulk of the crystal, indicating the bending stress associated with the crystal’s thickness. The uniformly distributed electric bias field inside the crystal constrains the carrier transport process, provides a consistent geometric variation and electrical contact between the crystal and the electrodes, and further ensures a high effective collection area and enhanced collection capacity for photocarriers, even when the device is subjected to bending. The degradation percentage of the sensitivity after 100 bending cycles is 12.7% and 6.6% for thick (100 μm) and thin (10 μm) samples, respectively. All the simulated and experimental results indicate that PbI2 crystal, when used to construct a 3D-structured device of appropriate thickness, is a promising candidate for the development of flexible x-ray photodetectors.

Enhancing the hydrogen generation of TiO2 nanoparticles by decorating its surface with BiI3 and PbI2 quantum dots

This work reports the performance of TiO2/BiI3 and TiO2/PbI2 nanocomposites for hydrogen generation. BiI3 and PbI2 quantum dots (QDs) were grown on TiO2 (P25 Degussa) using a fast injection method. According to the analysis by X-ray diffraction, the nanocomposites have a mixture of anatase, rutile and cubic phases from TiO2, BiI3 and PbI2. The images obtained from transmission electron microscopy revealed that the TiO2 support have sizes in the range of 70–220 nm while the QDs of BiI3 and PbI2 (co-catalysts) grown on TiO2 have sizes in the range of 12–17 nm. The presence of these iodides on TiO2 created oxygen vacancies defects (confirmed by photoluminescence measurements) that extended the light absorption of TiO2 from the UV to the VIS range. According to the results from the photocatalytic experiments for hydrogen generation (achieved using pure water and UV-VIS light), the hydrogen generation rates produced by the TiO2/BiI3 and TiO2/PbI2 nanocomposites were 437–580 times, 81–108 times and 21–30 times, higher than these for pure TiO2, PbI2 and BiI3, respectively. The maximum hydrogen generation rates of the TiO2/BiI3 and TiO2/PbI2 nanocomposites were 290.7 and 219.2 μmol h−1 g−1, respectively. In addition, the TiO2/BiI3 and TiO2/PbI2 nanocomposites contained defects that acted as electron trapping centers, which in turn, delayed the electron-hole recombination and this favored the photocatalytic generation of H2. Moreover, the heterojunction formed between the TiO2 and the iodides allowed the transfer of electrons from the conduction band of TiO2 toward the conduction band of the iodides, creating a “sink” for the electrons which delayed the electron hole recombination. The results presented here demonstrated that the deposition of iodide co-catalyst on TiO2 is a feasible option to enhance the hydrogen generation.

Unraveling the Impact of Halide Mixing on Crystallization and Phase Evolution in CsPbX3 Perovskite Solar Cells

Summary All-inorganic perovskite solar cells (PSCs) have attracted wide attention for their excellent thermal stability. However, the detailed crystallization process and complicated phase-transition mechanism of the CsPbX3 film with different halide compositions (I, Br, Cl) remain mysterious. In this study, systematic investigations are performed via state-of-art in situ grazing-incidence wide-angle X-ray scattering to understand the role of the halide elements in all-inorganic perovskite crystallization kinetics, phase-transition, and stabilization mechanism as well as how film morphology and grain size are affected. Based on these results, we were able to fabricate high-performance ternary halide (I, Br, Cl) all-inorganic PSCs through a precise compositional engineering. Our results provide guidance for an in-depth understanding of all-inorganic perovskite materials and pave the way to obtain high-performance all-inorganic PSCs.

Insight on the optoelectronics and enhanced dielectric properties of strontium decorated PbI2 nanosheets for hot carrier solar cell applications

Dielectric properties determine by electric field distributions play a decisive role in energy harvesting and storage applications. In this context, strontium decorated lead iodide nanosheets (Sr:PbI2) are prepared, and its vibrational and dielectric properties are studied. The bandgap changes are explained by Brustein-Moss effect and renormalization process. Raman spectral studies reveal that introducing Sr atoms into PbI2 lattice enhance the lifetime of LO phonon through bottleneck effect. Subsequently, the dielectric constant (ε′) values of 5 wt% Sr:PbI2 are increased 20% than pure PbI2. The results conclude that the vibrational properties of Sr decorated PbI2 nanosheets are much significant for hot carrier solar cell devices.

Enhancement in photodetection properties of PbI2 with graphene oxide doping for visible-light photodetectors

Herein, lead iodide (PbI2) nanorods/graphene oxide (GO) nanocomposites have been successfully achieved at low temperature via microwave-assisted syntheses route. The X-ray diffraction (XRD) analysis confirm good crystallinity and absence of any impurity in the prepared hybrid nanostructures which further confirmed through Raman analysis. The XRD and Raman study also confirm the doping of GO in 2H polytypic PbI2 structure. The average crystallite size of PbI2 is calculated to be 20 nm which found to be increased to 53 nm in the case of GO-PbI2 for high intensity peak. Scanning electron microscope (SEM) images reveal that the GO sheets are decorated with PbI2 nanoparticles and nanorods. The absorption spectra of PbI2 was found to broaden whereas energy bandgap of GO-PbI2 decreases to 2.83 eV in compare to 3.24 eV for PbI2. The effect of graphene oxide doping on photodetector performance of PbI2 was elucidated by measuring the I-V characteristics under 532 nm laser light illumination. The pure PbI2 exhibits a stable and reversible photodetector performance with responsivity of 0.060 AW−1, detectivity of 6.38 × 1010 Jones, EQE of ∼14 % and response time of 224 ms. For GO-doped PbI2, these parameters were found to be improved to 0.182 AW−1, 1.79 × 1011 Jones, ∼42 %, and 128 ms, respectively.

Microwave-assisted synthesis of Mg:PbI2 nanostructures and their structural, morphological, optical, dielectric and electrical properties for optoelectronic technology**Project supported by the Deanship of Scientific Research at King Khalid University (Grant No. R.G.P1/207/41), the Deanship of Scientific Research at Princess Nourah bint Abdulrahman University through the Fast-track Research Funding Program, and Deanship of Research, University of Hail.

This work reports the cost-effective growth of Mg:PbI2 nanostructures with 0, 1, 2.5 and 5.0 wt.% Mg doping concentrations. Structural, vibrational, morphological properties are analyzed using x-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). XRD and Raman studies confirm the monophasic hexagonal system of Mg:PbI2, and no additional impurity peaks are detected. The Scherrer formula is used to determine sizes of crystallites to be in the range of 47–52 nm. EDX/SEM e-mapping analyses confirm the incorporation of Mg in PbI2 matrix and its uniform distribution throughout the sample. The hexagonal nanosheet- and nanoplate-like morphologies are detected in SEM images for pure and Mg-doped PbI2. An optical band gap of nanostructures is obtained from Tauc’s relation to be in the range 3.0–3.25 eV. Dielectric and electrical properties are found in significant enhancement as Mg doping in PbI2 matrix, also the conduction mechanism is discussed.

Purely physical fabrication of 10 cm × 10 cm, highly uniform PbI2 thin films on rigid and flexible substrates for x-ray photodetection application

Lead iodide, PbI2, is one of the promising metal halide materials used for x- and γ-ray detection; it is also a key constituent of organometallic halide perovskites for low-cost solar cells. Here, we report a mature technology for the fabrication of microelectronic devices—an electron beam evaporation method to prepare highly uniform PbI2 thin films with a size of up to 10 cm × 10 cm on various rigid and flexible substrates at room temperature; the fabricated x-ray detectors show a consistent detection performance. The detection performance of the PbI2 thin film based flexible detectors demonstrate high robustness and stability under various bending states, suggesting themselves as potential candidates for the development of next-generation, large-area, and flexible x-ray detecting devices by using pure PbI2 films.

Formation of PbMnI2 alloys: Structural, photoluminescence and nuclear quadrupole resonance studies

The structural, optical and nuclear quadrupole resonance (NQR) measurements of PbMnI2 alloys were carried out. This allows us to study the peculiarities of the formation of such alloys. It was found that pure PbI2 and Pb1-XMnXI2 crystals with X = (0.03–0.05) have the phase of 2H-polytype. It was shown that the investigated alloys can be presented as the crystal regions of Pb1-XMnXI2 solid solutions, embedded in PbI2 crystal matrix. These formations can be considered as platelet-shaped nanoparticles with a surface of several microns and a thickness of several tens of nm. Thus, PbMnI2 alloys are heterogeneous PbI2–PbMnI2 nanocomposites. The results of NQR spectra measurements also show that Mn2+ ions preferably replace Pb2+ ions in the crystalline layers. Here, the local deformations occur because the radii of Pb2+ and Mn2+ ions differ significantly. The broadening of optical and NQR lines is due to the presence of both these deformations and the crystal field fluctuations, which are characteristic of semiconductor solid solutions.

An impact of Cr-doping on physical properties of PbI2 thin films facilely deposited by spin coating technique

Abstract Herein, we report the effect of Cr-doping concentrations (0.0, 1.0, 3.0, 5.0, 7.5 wt%) on the physical properties of PbI2 thin films fabricated through cost effective spin coating method. The XRD pattern reveals that the fabricated PbI2 thin films have 2H-polytype structure. The Cr-doping in PbI2 thin films were confirmed via Raman spectra and EDX/SEM mapping. The surface morphology of pure PbI2 films reveals that the spherical nanoparticles are uniformly assembled throughout the surface of PbI2 films and morphology of the film enormously change with Cr-doping. The optical study shows that the parameters such as dielectric constant, refractive and absorption indexes primary rises for Cr-content up to 1% and later start decreasing for concentrations >1%. The direct band gap of Cr-doped PbI2 thin films was found to be decreased to 2.34 eV in comparison to 2.43 eV of pure PbI2 thin films. The optical conductivity for pure PbI2 thin films was evaluated and found to be decreases with Cr-doping concentrations. Finally, nonlinear optical properties of the fabricated thin films were investigated and observed that the optical susceptibilities first increase for 1% Cr-doping concentration and systematically decreases for higher doping concentrations.

Achieving Reproducible and High-Efficiency (>21%) Perovskite Solar Cells with a Presynthesized FAPbI3 Powder

The conventional precursor mixture based on highly pure and expensive PbI2 (purity >99.99%) is problematic in commercializing perovskite solar cells (PSCs) because of a large deviation in the batch-to-batch photovoltaic performance due to underlying nonstoichiometry and/or the nonperovskite phase. Here, we report on reproducibly efficient (>21%) PSCs based on the ambient-temperature-stable δ-phase FAPbI3 powder, synthesized by reacting PbI2 (either homemade or low-grade commercial product with purity <99%) with formamidinium iodide (FAI) at room temperature (∼93% yield). X-ray diffraction patterns confirm that annealing the spin-coated film leads to phase purity of cubic α FAPbI3. As compared to the conventional precursor mixture based on PbI2 (purity = 99.9985%), significantly reducing defects in the powder-based film is responsible for the stable and reproducible efficiency. In addition, the homogeneous light-intensity-dependent surface photocurrent contributes to the reproducibility of photovoltaic per...

Preparation of PbI2 Microflakes by pH-Controlled Double-Jet Precipitation

Introduction: Pure PbI2 crystal particles with a flaky shape were prepared by a pH-constant double-jet precipitation process, which has the significant advantages of easy operation and scaling-up. It was found that a pH below 5.0 of the mixing solution is the appropriate range for the formation of pure PbI2 phase, while at a pH above 5.0, the PbIOH phase would appear immediately and decrease its solubility in DMF (dimethylformamide) for the preparation of a high-quality film of perovskite solar cells. Materials and Methods: Various instruments, including XRD, FTIR, SEM/EDS were used to characterize the precipitated particles obtained under different experimental conditions, and the effect of various parameters, including pH, concentration of the lead ions, feeding rate, and the characteristics of the surfactants on the particle was investigated systematically. Thermodynamic calculation of species distribution in the solution systems of Pb2+-I-- H2O, Pb2+-I--Cit-H2O and Pb2+-I--EDTA-H2O were carried out to identify the indispensable role of pH on the formation of highly pure lead iodide crystals. The crystallization of PbI2 was regarded as the basis of the formation of flake-like products, which was also strongly dependent on the pH value of the solution. Results: It was found that at a low concentration of the PbI2 precursor, such as with very dilute lead ions or with a very slow feeding rate, the XRD reflection peaks at 12.67°, 38.67° and 52.39° will dominate, while the peaks at 25.91°, 34.27°, and 39.51° will become dominant in the case of high concentration. The lead iodide particles were tested by mixing them in DMF, and it was found that the samples precipitated at a pH of 2 and 4 could dissolve and form a homogeneous solution easily, while the sample produced at a pH of 6 would form a turbid suspension, and could not dissolve completely to obtain a clear solution. Conclusion: The results presented in this work provide detailed and significant information about the synthesis of highly pure PbI2 which may be applied in the fabrication of perovskite solar cells.

Fabrication and characterization of La doped PbI2 nanostructured thin films for opto-electronic applications

Herein, we report a facile, cost-effective, solution processed fabrication method for pure and lanthanum (La3+) doped lead iodide (PbI2) thin films and investigated structural, optical, dielectric and electrical properties. Synthesis of PbI2 was confirmed by X-ray diffraction (XRD) and FT-Raman spectroscopy analyses. The fabricated films were grown along (001) plane, with crystallite size in the range of 12–14 nm and observed that crystallinity increases and defects decreases with the increase of La doping concentration. The morphology of fabricated films was observed to be spherical nanoparticles assembled nanosheets, distributed uniformly throughout the films. Moreover, homogeneous La doping in PbI2 was seen via EDX elemental mapping image. Optical band gap was calculated from Ultra violet–visible–near infrared (UV–Vis–NIR) spectra. The band gap of pure PbI2 film was noticed ∼2.44 eV which increase to 2.63 eV for 3% La3+ doped film. Absorption index, refractive index and dielectric constant values were calculated from optical data and found to be strongly dependent on incident photon energy and all parameters show higher values for La doped PbI2 films. I-V characteristics of pure and La-doped PbI2 thin films were carried out in the device configuration viz. FTO/PbI2 (or La-doped PbI2)/Au at room temperature. I-V curve for the pure PbI2 films shows the ohmic behavior while La doped PbI2 films shows non ohmic behavior attributed to space charge limited current. The electrical resistivity values for pure PbI2 film is found to be very high about 1.8 × 1011 Ω-cm.

From Lead Iodide to a Radical Form Lead‐Iodide Superlattice: High Conductance Gain and Broader Band for Photoconductive Response

Superlattice materials offer new opportunities to modify optical and electrical properties of recently emerging 2D materials. The insertion of tetraethylbenzidine (EtDAB) into interlamination of the established 2D PbI2 semiconductor through a mild solution method yielded the first lead iodide superlattice, EtDAB⋅4PbI2 (EtDAB=tetraethylbenzidine), with radical and non-radical forms. The non-radical form has a non-ionic structure that differs from the common ionic structures for inorganic-organic hybrid lead halides. The radical form shows five orders of magnitude greater conductance and broader photoconductive response range (UV/Vis → UV/Vis-IR), than pure PbI2 and the non-radical form of the superlattice.

From Lead Iodide to a Radical Form Lead‐Iodide Superlattice: High Conductance Gain and Broader Band for Photoconductive Response

AbstractSuperlattice materials offer new opportunities to modify optical and electrical properties of recently emerging 2D materials. The insertion of tetraethylbenzidine (EtDAB) into interlamination of the established 2D PbI2 semiconductor through a mild solution method yielded the first lead iodide superlattice, EtDAB⋅4PbI2 (EtDAB=tetraethylbenzidine), with radical and non‐radical forms. The non‐radical form has a non‐ionic structure that differs from the common ionic structures for inorganic–organic hybrid lead halides. The radical form shows five orders of magnitude greater conductance and broader photoconductive response range (UV/Vis → UV/Vis‐IR), than pure PbI2 and the non‐radical form of the superlattice.

Iodine Induced PbI2 Porous Morphology Manipulation for High‐Performance Planar Perovskite Solar Cells

The quality of the perovskite film has a vital influence on the performance of perovskite solar cells and it is quite desirable to simultaneously manipulate the crystallization and morphology of the perovskite film. In this study, conventional PbI2 is replaced with a PbI2/I2 mixed precursor during the first step of sequential deposition, causing the formation of a PbI2 porous nanostructure. By changing the content of I2 in the precursor, the morphology of the PbI2 film as well as the resulting perovskite film can be successfully modulated. With an optimal content of I2, a high‐quality perovskite film with a pure phase and smooth surface can be achieved. As a result, the conversion efficiency of perovskite solar cells using a PbI2/I2 mixed precursor can be as high as 18.63%, compared to 16.89% for the reference device through traditional sequential deposition with a pure PbI2 precursor.

PbI2/CH3NH3Cl Mixed Precursor–Induced Micrometer‐Scale Grain Perovskite Film and Room‐Temperature Film Encapsulation toward High Efficiency and Stability of Planar Perovskite Solar Cells

AbstractThe power conversion efficiency and the stability are the most important figures of merit for perovskite solar cells which attract increasing attention in recent years. Herein, the growth of high‐quality perovskite films with micrometer‐scale grain size through sequential deposition is first reported using PbI2/CH3NH3Cl mixed precursors during the first step of deposition. The amount of CH3NH3Cl in the precursor has a great influence on the morphology of perovskite films and the device performance. Compared with traditional sequential deposition with pure PbI2 in the first step, this method renders the perovskite solar cells with an improved power conversion efficiency up to 18.7% and reduced hysteresis. In addition, the fluorinated carbon film prepared at room temperature is reported as an encapsulation layer for perovskite solar cells. The compact and hydrophobic thin film can effectively isolate the device from moisture and oxygen, leading to the largely improved stability in the air. This study not only reveals the effect of chlorine doping on perovskite film formation in the first step of sequential deposition, but also provides a new film encapsulation strategy to improve the device stability in ambient air toward future application.

CH3 NH3 PbI3 and HC(NH2 )2 PbI3 Powders Synthesized from Low-Grade PbI2 : Single Precursor for High-Efficiency Perovskite Solar Cells.

High-efficiency perovskite solar cells are generally fabricated by using highly pure (>99.99 %) PbI2 mixed with an organic iodide in polar aprotic solvents. However, the use of such an expensive chemical may impede progress toward large-scale industrial applications. Here, we report on the synthesis of perovskite powders by using inexpensive low-grade (99 %) PbI2 and on the photovoltaic performance of perovskite solar cells prepared from a powder-based single precursor. Pure APbI3 [A=methylammonium (MA) or formamidinium (FA)] perovskite powders were synthesized by treating low-grade PbI2 with MAI or FAI in acetonitrile at ambient temperature. The structural phase purity was confirmed by X-ray diffraction. The solar cell with a MAPbI3 film prepared from the synthesized perovskite powder demonstrated a power conversion efficiency (PCE) of 17.14 %, which is higher than the PCE of MAPbI3 films prepared by using both MAI and PbI2 as precursors (PCE=13.09 % for 99 % pure PbI2 and PCE=16.39 % for 99.9985 % pure PbI2 ). The synthesized powder showed better absorption and photoluminescence, which were responsible for the better photovoltaic performance. For the FAPbI3 powder, a solution with a yellow non-perovskite δ-FAPbI3 powder synthesized at room temperature was found to lead to a black perovskite film, whereas a solution with the black perovskite α-FAPbI3 powder synthesized at 150 °C was not transformed into a black perovskite film. The α↔δ transition between the powder and film was assumed to correlate with the difference in the iodoplumbates in the powder-dissolved solution. An average PCE of 17.21 % along with a smaller hysteresis [ΔPCE=PCEreverse -PCEforward )=1.53 %] was demonstrated from the perovskite solar cell prepared by using δ-FAPbI3 powder; this PCE is higher than the average PCE of 17.05 % with a larger hysteresis (ΔPCE=2.71 %) for a device based on a conventional precursor solution dissolving MAI with high-purity PbI2 . The smaller hysteresis was indicative of fewer defects in the resulting FAPbI3 film prepared by using the δ-FAPbI3 powder.

High performance hole transport material free perovskite solar cells from a low pure PbI2 source using a facile solid-gas reaction process

Abstract Preparing CH3NH3PbI3 perovskite solar cells from a low pure lead source is highly desirable for cutting down the fabrication cost of perovskite solar cells. To avoid the low solubility problem of low pure PbI2 source in the commonly used solvent, PbI2 first reacts with HI solution to produce highly soluble HPbI3 compound, then CH3NH3PbI3 perovskite film is obtained through a solid-gas reaction between HPbI3 film and CH3NH2 vapor. By optimizing the concentration of HPbI3 precursor solution, highly uniform perovskite films are obtained. Hole transport material free perovskite solar cells fabricated via this facile method exhibit an average power conversion efficiency of 12.90% and a maximum power conversion efficiency of 13.21%, which are comparable to the performances of perovskite solar cells prepared from high pure PbI2 sources.