Lead-free Perovskite Materials Research Articles

Humidity Sensing Applications of Lead-Free Halide Perovskite Nanomaterials.

Over the past decade, perovskite-based nanomaterials have gained notoriety within the scientific community and have been used for a variety of viable applications. The unique structural properties of these materials, namely good direct bandgap, low density of defects, large absorption coefficient, high sensitivity, long charge carrier lifetime, good selectivity, acceptable stability at room temperature, and good diffusion length have prompted researchers to explore their potential applications in photovoltaics, light-emitting devices, transistors, sensors, and other areas. Perovskite-based devices have shown very excellent sensing performances to numerous chemical and biological compounds in both solid and liquid mediums. When used in sensing devices, Perovskite nanomaterials are for the most part able to detect O2, NO2, CO2, H2O, and other smaller molecules. This review article looks at the use of lead-free halide perovskite materials for humidity sensing. A complete description of the underlying mechanisms and charge transport characteristics that are necessary for a thorough comprehension of the sensing performance will be provided. An overview of considerations and potential recommendations for the creation of new lead-free perovskite nanostructure-based sensors is presented.

Lead-free bilayer heterometallic halide perovskite with reversible phase transition and photoluminescence properties

The layered heterometallic halide perovskites, as a newly explored material, have attracted great scientific attention. As one of the representatives of perovskite, lead-free or lead-substituted perovskite materials are widely applied in photovoltaic, sensors, catalysis, detectors and other fields. Therefore, it is urgent to carry out more systematic exploration and expand applicable preresearch, so as to make more interesting discoveries in this new hot spot. As an interesting candidate, heterometallic compounds will introduce more structural adjustability and novel physical properties, which is the main feature to be selected as the research hotspot. Here, we reported a lead-free bilayer heterometallic Ruddlesden-Popper (RP) type perovskite, [(MACH)2CsAgBiBr7] (MACH = cyclohexanemethylamine), which possesses a reversible phase transition at 379.6 K/375.1 K during heating-cooling cycle. Besides, it exhibits reddish-brown light emission under 365 nm, meanwhile, CIE chromaticity coordinate is (0.32, 0.45) on the yellow side and correlated color temperature is about 6000 K. Moreover, both the experimental data and theoretical calculation results suggest that [(MACH)2CsAgBiBr7] shows indirect semiconducting characteristics. In summary, this work will inspire the design of lead-free heterometallic perovskite materials for the application of sensors and light-emitting diodes (LEDs) fields.

Enhanced near-ambient temperature energy storage and electrocaloric effect in the lead-free BaTi0.89Sn0.11O3 ceramic synthesized by sol–gel method

Lead-free perovskite materials with high performance have high potential in clean energy storage applications and developments of electrocaloric devices. This work reports structural, dielectric, ferroelectric, energy storage, and electrocaloric properties near the ambient temperature in barium stannate titanate (BaTi0.89Sn0.11O3, BTS11) ceramic prepared by a sol–gel method. A single perovskite structure formation was confirmed using the X-ray diffraction analysis. Average grain size of 18.5 µm was found by the mean of the SEM micrograph with a density of 5.91 g/cm3. The multiphase coexistence at very near ambient temperature was proved using temperature-dependent micro-Raman measurements and differential scanning calorimetry. The BTS11 ceramic exhibits a high dielectric constant of 15,460 and a low dielectric loss (< 0.055) in a broad temperature range. Moreover, a high energy storage density of 122 mJ/cm3 was shown with an efficiency of 79%, a maximum value of electrocaloric temperature change (ΔT) of 0.86 K, and finally, an electrocaloric responsivity (ΔT/ΔE) of 0.24 K.mm/kV at the external electric field change of 35 kV/cm near ambient temperature. The enhanced dielectric, ferroelectric, and electrocaloric properties make BTS11 ceramics a great candidate for solid-state cooling technology and high energy storage applications near ambient temperature.

Optoelectronic Properties Prediction of Lead-Free Methylammonium Alkaline-Earth Perovskite Based on DFT Calculations.

Dynamical stability plays an essential role in phase transition and structure, and it could be a fundamental method of discovering new lead-free perovskite materials. The perovskite materials are well-known for their excellent optoelectronic properties, but the lead element inside could be a hindrance to future development. This research is trying to predict the promising cation candidates in the high-temperature application for lead-free perovskite materials from the replacement of lead in MAPbCl3 (MA = methylammonium) with alkaline-earth cations. The alkaline-earth cations are of a stable positive divalent sort, which is the same as Pb, and most of them are abundant in nature. Therefore, by improving the dynamical stability, the Mg2+, Ca2+, and Sr2+ cations replacement of lead ions could stabilize the perovskite structure by decreasing the imaginary part of phonon density of states. Finally, the density functional theory results show that the MACaCl3 could be a dynamic stable lead-free methylammonium perovskite material with an ultrawide band gap (5.96 eV).

Tunable lanthanum doping in double perovskite films for read-only memory

Rare earth ions have been widely investigated as active dopants in various materials because of their distinct optical, electronic and magnetic properties. Halide perovskite resistive memories have attracted increasingly recent interest for tremendous potential applications in computation and data storage techniques. However, it remains unexplored to implement rare earth doping strategy for tuning perovskite resistive memories. Here, we report read-only memories based on environment-friendly and air-stable lead-free double perovskite Cs2AgBiBr6 films, which is particularly tuned by rare earth La3+ doping. We use the vacuum sublimation and solution processing method to obtain Cs2AgBiBr6 crystals doped by different content La3+, and fabricate resistive memory devices based on doped Cs2AgBiBr6 films. The simplest sandwich-like structure composed of ITO/La-doped-Cs2AgBiBr6/Ag only is designed in cross-bar array architecture with high-integration and simple operation. The resistive memory device of La-doped Cs2AgBiBr6 films demonstrate a typical write-once-read-many-times (WORM) behavior with low onset voltage of 1 V and long retention time of 12000 s. In particular, the ON/OFF ratio of the La-doped Cs2AgBiBr6 film is 100 times higher than that of the undoped Cs2AgBiBr6 film. This study provides a new insight to design and manipulate memory devices based on lead-free halide perovskite materials through doping effect of rare earth ions.

Efficient red photoluminescence in holmium-doped Cs2NaInCl6 double perovskite

Metal halide perovskites with efficient and stable self-trapped exciton emission have attracted considerable attention for next-generation solid-state lighting owing to their ultrabroadband emission. However, it remains challenging to widen the color gamut and realize high color-rendering index due to the lack of highly saturated red color-emitting inorganic lead-free perovskite materials with narrow full width at half-maximum. Here, we report a lanthanide-codoped system (Cs2NaInCl6:Sb3+/Ho3+) that enables efficient blue and red emissions with photoluminescence quantum yields of up to 99% and 72%, respectively. The energy transfer efficiency in Ho3+-doped Cs2NaInCl6:Sb is up to 73%, which can overcome the weak absorption cross-section of the f-f transition of lanthanide ion and improve its luminescence performance. Benefitting from the efficient energy-transfer channel from the self-trapped excitons to Ho3+, the emission color is continuously tuned from blue to red by controlling the Ho3+-doping concentration.

Exploring the stability and physical properties of double perovskite Cs2SnI6 by doping the Cl/Br atom: A DFT study

In recent years, it is of great interest to develop stable and high efficiency lead-free perovskite materials. Double perovskite Cs2SnX6 (X = Cl, Br, I) shows excellent stability and tunable band gap. The stability, electronic, and optical properties of three mixed halide double perovskites Cs2SnI4Cl2, Cs2SnI4ClBr, and Cs2SnI4Br2 are studied in this work. The stability of three mixed halide compounds is slightly lower than that of Cs2SnI6. The trend of phase separation is found for the studied compounds. Compared with CsSnX3, the SOC effect is negligible for Cs2SnX6. Cs2SnI4Cl2 and Cs2SnI4ClBr have the same band gaps with 1.75 eV, while Cs2SnI4Br2 shows an optimum band gap with 1.56 eV. Although these mixed halide compounds display stronger absorption coefficients than Cs2SnI6 from 300 to 450 nm, the lower light absorption capacity is observed between 450 and 800 nm.

Atomic-scale polar vortices in Na0.5Bi0.5TiO3 grains

Ferroelectric materials have great potential applications in non-volatile ferroelectric random access memories because of the singularity of one-dimensional topological defects. In this paper, we have found for the first time the atomic-level dipole rotations of vortex structures in crystalline materials. By the aberration-corrected high resolution scanning transmission electron microscopy (STEM), the atomic-scale multiple rotation domains and polar vortices in Na0.5Bi0.5TiO3 (NBT) grains have been clearly observed in lead-free perovskite NBT. Meanwhile, nanobeam electron diffraction experiments provided the strong evidences of the coexistence of tetragonal, orthorhombic and rhombohedra phases at room temperature. These polar vortices are constructed by the competition of these atomic-scale polar domains, which are originated from the multiphase coexistence of NBT and can be well confirmed by our theoretical calculations. These observations have put forward new implications for the creation of vortex topologies in crystalline materials without sophisticated thin-film technologies, and it can also help to understand the complicated polar mechanism in lead-free perovskite ferroelectric materials.

Research progress of ABX3-type lead-free perovskites for optoelectronic applications: materials and devices.

In recent years, lead halide perovskite materials have attracted great interest and are widely used in solar cells and light-emitting devices due to their high photoelectronic quantum yield, high color purity, high defect tolerance, long diffusion length, high carrier mobility, and bandgap tunability. However, the application of lead halide perovskites is limited due to the presence of Pb, making lead-free perovskites an important substitute due to their same crystal structure and similar properties. Although some reports have been made on lead-free perovskite materials, there are still great challenges to realize their application due to their poor stability, easy phase transition, and low photoelectric conversion efficiency. Here, we mainly summarize the development and application of ABX3-type lead-free halide perovskite materials, especially in optoelectronic devices. The article first introduces the lattice and energy band structure, the optoelectronic properties of lead-free perovskites, including the research method of lead-free perovskites, and then analyzes the reasons for the low luminous efficiency and poor stability of lead-free perovskite materials. Second, the development history and current situation of lead-free perovskites in different optoelectronic device applications are summarized. Finally, we present the challenges and prospects for the future development of lead-free perovskites.

Lead-free perovskite solar cell byUsing SCAPS-1D: Design and simulation

The efficiency of photovoltaic systems of perovskite materials based on organic–inorganic halide has increased and they are nearing commercialization. Lead-free perovskite materials have recently attracted the interest of researchers and the scientific community due to the toxicity issue and harmful lead-based perovskite materials. Tin, like lead (Pb) is a group 14 metals; hence, it is the most likely substitute. We use SCAPS-1D numerical simulation to optimize the device efficiency of a lead-free n-i-p based planar hetrostructure perovskite solar cell composed of intrinsic-CH3NH3SnI3 methyl ammonium tin iodide (MASnI3) as an i- and p-layer Spiro-OMeTAD with SnO2 for the n layer. Conclusions show that the absorber layer has a thickness of 600 nm, which is required for optimal cell performance and efficiency. The thickness and defect density of this absorber layer was taken into account, absorption coefficient is inversely proportional to defect density. The performance of device worsens when the defect density of absorber layer increases. The thickness and defect density of absorber layer was carefully tuned to get maximum solar cell performance and we observed an efficiency of 22.21 %, current density (JSC) of 33.8636 mA/cm2, VOC of 0.989 V and FF of 66.33 % at 600 nm thickness of absorber layer.

Double perovskite Cs2AgBiBr6 radiation sensor: synthesis and characterization of single crystals

Single crystals of lead-free halide double perovskite Cs2AgBiBr6 sensor material manifest a remarkable potential for application in radiation detection and imaging. In this study, the purity and crystallinity of solution-grown Cs2AgBiBr6 single crystals with cubic Fmoverline{3}m symmetry have been corroborated by powder XRD measurements, while the single crystal XRD patterns reveal the dominant {111} lattice planes parallel to the sample surfaces. A wider range of lower resistivity values (106–109 Ωcm) was obtained from the I-V measurements compared to the 1.55 × 109–6.65 × 1010 Ωcm values from the van der Pauw method, which is typically higher for the Ag than for the carbon paint electrodes. Charge-carrier mobility values estimated from the SCLC method for the carbon paint-Cs2AgBiBr6 (1.90–4.82 cm2V−1 s−1) and the Ag-Cs2AgBiBr6 (0.58–4.54 cm2V−1 s−1) including the density of trap states (109–1010 cm−3) are comparable. Similar values of 1.89 cm2V−1 s−1 and 2.36 cm2V−1 s−1 are derived from the Hall effect measurements for a sample with carbon and Ag electrodes, respectively. The key electrical parameters including the X-ray photoresponse measurements indicate that the Cs2AgBiBr6 samples synthesized in this study satisfy requirements for radiation sensors.Graphical abstract

Optical humidity sensors based on lead-free Cu-based perovskite nanomaterials.

Organometallic halide perovskite materials possess unique and tunable optical properties with a wide range of optoelectronic applications. However, these materials suffer from humidity-driven degradation in ambient atmospheres. In this paper we investigate stable copper-based perovskite nanocrystals for potential use in humidity sensors, specifically examining their unique humidity-dependent optical properties and reversibility. We controlled stoichiometric ratios of Cu-based perovskites and demonstrated that (methylammonium)2CuBr4 nanocrystals showed excellent reversible physisorption of water molecules. These perovskite nanocrystals exhibited reversible hydro-optical properties, including transparency changes in response to variations in relative humidity under ambient conditions. The perovskite nanomaterial humidity sensor was highly reliable and stable, with a linear correlation in a relative humidity range of 7% to 98%. Accordingly, the lead-free Cu-based perovskite materials developed herein have the potential to be employed as real-time, self-consistent humidity sensors.

Numerical simulation study of lead-free double perovskite solar cell through computation method

Recently, the development of lead-free double perovskite materials based PSCs have received remarkable attention of researchers. Various types of experimental and theoretical studies have been reported to enhance the efficiency of the device. In the present investigations, we have performed computational based study to analyze the device response with lead-free double perovskite light absorbing layers Dy2NiMnO6(DNMO), Eu2NiMnO6(ENMO) and TiO2 as electron transport layer (ETL) and CuI as hole transport layer (HTL). The thickness of absorber layer is optimized with SCAPS-1D software and analyzes the photovoltaic parameters including quantum efficiency (QE) with varying the thickness of absorber layers of PSCs. Finally, the maximum device efficiency of 11.72% for DNMO and 12.63% for ENMO was observed at optimized thickness of 1.4 μm. The QE analysis also exhibited that the thickness of absorber play major role in device performance and enhanced as thickness of absorber increases.

Recent progress of lead-free bismuth-based perovskite materials for solar cell applications

In this paper, the progress made in optimizing the structures, composition, crystallization kinetics and device performance of bismuth-based perovskite materials is reviewed to show some of the opportunities and challenges they have encountered.

Lead-Free Ultra-Wide Direct Bandgap Perovskite EACaI3

Recently, perovskite-based light-emitting devices (LEDs) have been invested with near-infrared, red, green, and blue emissions. And, short-wavelength perovskite LEDs targeted at violet emission remain a significant challenge. Moreover, the majority of previously reported devices were focused on the lead-containing halide perovskites. In this research, for the first time, EACaI₃ (270 nm) was proposed as ultraviolet-C potential lead-free perovskite material with direct ultra-wide bandgap property with 0.03&#x0025; imaginary part of phonon density of state. The perovskite EACaI₃ has dynamic stability and could be used for devices demonstrated with excellent working stability. These results suggest that the lead-free EACaI₃ are potentially attractive candidates for preparing environment-friendly and stable ultra-wide band gap device.

Transition Metal Ions in Methylammonium Chloride Perovskites.

Organic–inorganic perovskite materials have become star materials for future wide band gap optoelectronics due to their excellent optical and electrical properties. However, the lead ions inside perovskites have become a crucial environmental issue in the commercialization of wide band gap perovskite devices . This research tries to find the structure and properties of lead-free perovskite materials by screening Sn2+ and transition-metal ions to replace Pb2+ within the methylammonium (MA)-based chloride perovskite and find out a new two-dimensional structure of MA-based transition-metal ion chlorides. Overall, MAZnCl3 may be a potential ultraviolet-C luminescent material with a stable two-dimensional structure with a wide band gap of 5.64 eV, which is suitable for ultraviolet-C luminescence applications.

Investigation of lead-free MASnI3-MASnIBr2 tandem solar cell: Numerical simulation

Lead-free perovskite materials have attracted noteworthy interest for photovoltaics as they are free from toxicity and instability issues encountered in lead-based perovskites. In this work, we report on a simulation study of a two-terminal monolithic all lead-free tandem solar cell. The (MASnI3) cell with 1.3 eV bandgap is used as a bottom cell and the top cell is (MASnIBr2) with a bandgap of 1.75 eV. The calibration of the standalone bottom and top cells initially gives a conversion power efficiency (PCE) of 5.42% and 5.74%, respectively. After comprising these two initial sub-cells in a two-terminal all lead-free monolithic tandem cell, a tandem efficiency of 7.66% is obtained with a matching current is 10.36 mA/cm2 in this case. Based on parametric analysis, the values of perovskite doping, perovskite defect density and ETL/HTL affinity are optimized. The PCE of individual cells after enhancement has increased to 11.01% and 10.17% for bottom and top cells, respectively. As a result of the enhancement of the two cells, the tandem efficiency improves to 15.66% and the matching current also increases to 13.94 mA/cm2. In addition, the current matching point is tracked while changing the band gaps of bottom and top cells in the ranges of (1.1 eV–1.4 eV) and (1.55 eV–1.85 eV), and for the thicknesses in the ranges (150 nm–400 nm) and (150 nm–500 nm), respectively. The simulations done in this paper shows the significant influence of current matching point on the tandem cell performance. All simulations are performed by using SCAPS-1D under AM1.5G illumination.

Numerical simulations of 22% efficient all-perovskite tandem solar cell utilizing lead-free and low lead content halide perovskites

Lead-free or low lead content perovskite materials are explored in photovoltaic (PV) devices to mitigate the challenges of toxic lead-based halides. However, the conversion efficiency from such materials is far below compared to its counterparts. Therefore, to make a humble contribution in the development of lead-free or low lead content perovskite solar cells (PSCs) for future thin-film PV technology, a simulation study of tin (Sn) and Pb mixed halide (MAPb0.5Sn0.5I3, 1.22 eV) PSC is carried out in this manuscript. The device is further optimized in terms of transport layer and thickness variation to get 15.1% conversion efficiency. Moreover, the optimized narrow bandgap halide based device is further deployed in the monolithic tandem configuration with lead-free wide bandgap (1.82 eV) halide, i.e. Cs2AgBi0.75Sb0.25Br6, 1.82 eV (WBH) PSC, to mitigate the thermalization as well as transparent E g losses. Filtered spectrum, current matching, and construction of tandem J–V curve at the current matching point are utilized to design the tandem solar cell under consideration. Tandem device delivered short current density, J SC (15.21 mA cm−2), open-circuit voltage, V OC (1.95 V), fill factor, FF (74.09%) and power conversion efficiency, PCE (21.97%). The performance of the devices considered in this work is found to be in good approximation with experimental work.

Chances and challenges for tin perovskites

Tin perovskites are rising as the most promising lead-free perovskite material candidate that have drawn intensive attention in recent years. In this forum, the unique properties of tin perovskites and their applications in solar cells, light emission, and photodetectors are briefly introduced, along with the chances and challenges in each field.

Investigation on lead-free Mn-doped Cs2NaInCl6 double perovskite phosphors and their optical properties

Doping with transition metal ions in lead-free double perovskite material of Cs2NaInCl6 has been highly spotlighted for tailoring optical properties and advancing light-emitting applications. Herein, solvothermal method is employed to synthesizing Mn-doped Cs2NaInCl6 phosphors with a purpose of imparting new optical properties in the visible light region. X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy, thermogravimetric analysis, electron paramagnetic resonance and photoluminescence (PL) techniques confirm that Mn-doped Cs2NaInCl6 exhibits stable double perovskite crystal structure, good stability, and exceptional electronic properties. Mn-doped Cs2NaInCl6 also shows observable red fluorescence peaking at 610 nm with PL decay lifetime of about 0.21 ms and PL quantum yield of about 5%, owing to the 4T1→6A1 transition of the Mn d electron.