Pb-based Perovskites Research Articles

Impact of Spin-Coating Temperature on Morphology of Pb-Based Mixed Ion Perovskite Films and Their Solar Cell Performance

Impact of Spin-Coating Temperature on Morphology of Pb-Based Mixed Ion Perovskite Films and Their Solar Cell Performance

Improvement of Lead-Free Bismuth Based Perovskite Solar Cell Efficiency with Graded Bandgap Structure

Lead (Pb) halide perovskite has been identified as a promising light-harvesting material for perovskite solar cells (PSCs) with power conversion efficiency (PCE) exceeding 26%. However, the toxicity of Pb-based materials and poisonous environment are the main hindrances that limit their reliable applications. Bismuth (Bi)-based perovskite has shown high potential to replace conventional Pb-based perovskite, but the PCE of Bi-based perovskite solar cells is far lower than Pb-based. Despite the early exploration of Bi-based materials, a fundamental understanding of the material properties and developing strategies, including device design to improve performance, are needed immediately. Here, we report the graded bandgap design for Bi-halide PSCs, which aims to enhance the output current and PCE by maximizing the solar spectrum through device architecture. Titanium dioxide (TiO2) was used as an electron transport layer (ETL), and Spiro-OMeTAD was used as a hole transport layer (HTL) due to its facile implementation and high performance in electronic devices. The variation of iodine concentration in bi-doped iodide sets up bandgap tuning and the conductivity type of the layer. This conFigureuration produces cells with desirable performance that effectively absorb the photons in almost all parts of the solar spectrum. Both open circuit voltage (Voc) (940 mV) and fill factors (~58%) for the best cells have shown drastic improvement over single active layer device, and the short current densities (Jsc) measured are in the range (20-30) mAcm-2. The effects of quasi-electric fields instigated by the graded bandgap structure in the active layers upon the illumination current density and open-circuit voltage of a solar cell will be discussed further.

Efficient hole extraction by doped-polyaniline/graphene oxide in lead-free perovskite solar cell: a computational study

Abstract The intriguing behavior of doped polyanilinine/graphene oxide (PANI/GO) offers a solution to the pivotal problem of device stability against moisture in perovskite solar cell (PSC). Tunable bandgap formation of doped PANI/GO with an absorber layer allows effective flexibility for charge carrier conduction and reduced series resistance further boosting the cell performance. Herein, the L9 Orthogonal Array (OA) Taguchi-based grey relational analysis (GRA) optimization was introduced to intensify the key output responses. Furthermore, this work also delved into incorporating a Pb-free absorber perovskite layer, formamidinium tin triiodide (FASnI3), and concomitantly eluding the environmentally hazardous substance. The numerical optimization supported by statistical analysis is based on experimental data to attain the utmost peak cell efficiency. Taguchi’s L9 OA-based GRA predictive modeling recorded over one-fold enhancement over experimental results, reaching as high as 20.28% power conversion efficiency (PCE). Despite that, the PCE of the structures is severely affected by interface defects at the electron transport layer/absorber (ETL/Abs) vicinity, which is almost zero at merely 1 × 1014 cm−2, manifesting that control measures need to be taken into account. This work deduces the feasibility of ETL/Abs stack structure in replacing the conventional Pb-based perovskite absorber layer, while maximizing the potential use of doped PANI/GO as a hole transport layer (HTL).

Perovskite CsCuClxBr3-x Microcrystals: Band Structure, Photochemical Stability, and Photocatalytic Properties.

Although Pb-based metal halide perovskites (MHPs) have excellent photoelectric characteristics, its toxicity remains a limiting factor for its widespread application. In the paper, a series of CsCuClxBr3-x (x=1, 2, 3) MHPs microcrystals were developed and their hydrogen evolution performance in ethanol and HX (X=Cl, Br) were also studied. Among them, CsCuCl3 microcrystals exhibit high hydrogen evolution performance in both HX and ethanol, attributed to its longest average lifetime and suitable band structure. Additionally, the effect of different sacrificial agents on photocatalytic hydrogen production indicates that the photogenerated hole (h+) plays a critical role. MHPs can maintain a dynamic equilibrium of dissolution and precipitation in HX saturated aqueous solutions, thereby overcoming the stability issues associated with perovskite. The phase transition of CsCuClxBr3-x during photocatalysis is monitored by XRD technique. CsCuCl3 shows high stability in saturated HCl aqueous solution, and excellent photocatalytic performance with a hydrogen production rate of CsCuCl3 microcrystals reached 103.98 μmol g-1 at 210 min. Our study expands the development prospects of CsCuCl3 in the field of photocatalytic solar fuel generation.

Recent progress on the efficiency and stability of lead-free Cs2AgBiBr6 double halide perovskite solar cells

Abstract Within a decade, the power conversion efficiency (PCEs) of metal-halide perovskite solar cells (PSCs) move upward from 3.9% to 25.7%, making them competitive with current state-of-the-art silicon-based counterparts. This steepest growth of the PCEs suggests that the commercialization of this technology might be easing the energy transition from fossil fuel to renewable energy. However, a wide range of factors restricts the commercial viability of PSCs like their toxicity and instability. A crucial and difficult task in the field of PSCs is the replacement of Pb-based perovskite with non-toxic and eco-friendly material while maintaining the high-performance with improved stability. Cs2AgBiBr6double perovskites material seems to be very promising in this regard. This article reviews the recent progress in Cs2AgBiBr6 double PSC devices including the advancement of efficiency and stability. Here, the evolution of Cs2AgBiBr6 towards the application and fabrication of PSCs has also been discussed. This study also analyzed the impact of numerous environmental stresses, such as mechanical, thermal and optical stresses including the potential prospects in the case of Pb-free PSCs.

Synthesis of (9-Triptycyl)Tin Halides for Application in Perovskite Solar Cells

Solar cells using ABX3-type perovskite semiconductors are attracting attention due to their high photoelectric conversion efficiency. However, since most of them use lead (Pb), there is a need to develop Pb-free perovskite solar cells from the viewpoint of environmental impact. Perovskites using tin (Sn) have shown promise as an alternative material for Pb-based perovskites, but many challenges remain in achieving high performance because Sn2+ is more susceptible to oxidation than Pb2+. We have previously improved the quality of Sn-based perovskite films by scavenging the Sn4+ ions1 and applying different surface passivation methods.2,3 Most of the materials used for surface passivation have ammonium groups that can bind to the A-site of the perovskite lattice, or thiocyanate or carboxyl groups that can bind to the X-site. In this work, we present a novel modification method using halometallylene, a highly reactive chemical species that is expected to replace the metal at the B-site of the perovskite structure. For this purpose, we designed a series of halostannylenes, (Trp)XSn: (Trp = 9-triptycyl group, X = F, Cl, Br, and I). These compounds can be added to the precursor solution or applied to the surface of the perovskite layer.The reaction of 9-triptycyl lithium, which was generated by a lithiation of 9-bromotriptycene with n-BuLi, with SnX2 (X = Cl, Br) gave thermally stable yellow crystals of the product (Figure 1a). The crystals were determined to have a novel five-membered ring structure, {(Trp)XSn}5 (Figure 1b). In a coordinating solvent (dimethyl sulfoxide (DMSO) or pyridine), the compounds transformed into monomeric halostannylene complexes. From cyclic voltammetry (CV) measurements of (Trp)XSn: in DMSO solutions, the shift of the oxidation potential below any tin halide (SnX2, X = F, Cl, Br, and I) confirms that reaction active Sn2+ species, which can reduce Sn4+, were obtained. When (Trp)ClSn: was added to the solution of SnI4 in DMSO-d 6, in the 119Sn NMR spectra, a peak at –2030 ppm corresponding to SnI4 disappeared, and a new peak at –685 ppm was observed corresponding to SnI2. From these results, it’s expected that the compound will function as a reductant for Sn4+ generated in the perovskite precursor solution. In the presentation, we will further discuss the characteristics of (Trp)XSn: and its application to tin perovskite solar cells.1) T. Nakamura, A. Wakamiya et al, Nat. Commun. 2020, 11, 3008. 2) T. Nakamura, A. Wakamiya et al., ACS Appl. Mater. Interfaces 2022, 14, 56290. 3) S. Hu, A. Wakamiya et al., Adv. Mater. 2023, 35, 2208320. Figure 1

Single Layer of Crown Ether Enables Efficient, Stable, and Pb Leakage-Free Inverted Perovskite Solar Cells.

Significant challenges in ensuring long-term stability, addressing environmental safety issues, and improving efficiency have hindered the commercialization of inverted Pb-based halide perovskite solar cells (PeSCs). One reasonable approach to addressing these issues is to place an effective buffer layer between the perovskite active layer and the electrode. In this study, we demonstrate the use of crown ether, di-tert-butyl dibenzo-18-crown-6, as a single buffer layer to improve the efficiency, long-term stability, and environmental safety of PeSCs for the first time. The crown ether buffer layer suppressed Ag diffusion from the Ag metal electrodes, thereby improving the performance and lifetime of the device. In addition, it effectively captures Pb ions that may leak into the environment during the whole lifetime of devices, thereby enhancing the environmental safety of PeSCs. Furthermore, PeSCs incorporating crown ethers as buffer layers demonstrated enhanced stability in a nitrogen atmosphere and achieved a high power conversion efficiency of 22.8%. Consequently, this crown ether buffer layer offers an effective and straightforward strategy capable of achieving efficient, stable, and environmentally safe PeSCs.

Preferentially coordinating tin ions to suppress composition segregation for high-performance tin-lead mixed perovskite solar cells

Tin-lead mixed perovskites (TLPs) with a tunable and ideal bandgap exhibit great potential in approaching the Shockley–Queisser limit of power conversion efficiency (PCE). However, two critical issues are necessary to be addressed, including the oxidation of Sn2+ and negligible composition and phase segregation. The latter derives from the unbalanced crystallization rate between Sn- and Pb-based perovskites. Here, we report a strategy to address the above critical issues by introducing 3,4-Dihydroxybenzylamine hydrobromide (DHBABr) in the TLP precursor solution. DHBABr was revealed to promote the crystallization of FAPbI3 perovskite by suppressing the formation of crystalline DMSO-FA-Pb-I intermediates and retard the crystallization rate of FASnI3 by preferentially forming a steady amorphous DHBA-FA-Sn-I intermediate. This, therefore, balances the crystallization rate between Sn- and Pb-based perovskites. As a result, the spatial distribution of Sn/Pb ratio is much more uniform across the whole TLP film, which benefits the upscaling of the manufacturing process. Relying on this doping strategy accompanied by the surface passivation with DHBABr, which reduces the defect density of TLP, inhibits the oxidation of Sn2+, and optimizes the band alignment of the device, we have achieved a PCE of 22.44 % with Voc of 0.853 V and FF of 80.0 %, along with an enhanced long-term stability of T80 = 476 h under continuously light illumination in the champion device.

(Invited) Perovskite/Perovskite Tandem Photoelectrodes for Unassisted Water Splitting

The bandgap tunability and low-temperature processing make halide perovskites excellent candidates for achieving efficient and cost-effective tandem devices for solar cells and solar-driven water electrolysis devices. Here, we report our progress on fabricating perovskite/perovskite tandem cells consisting of two solution-processed perovskite subcells for unassisted water-splitting applications. The perovskite/perovskite tandem photoelectrodes are achieved by monolithically integrating a wide-bandgap (1.7 – 2.1 eV) Pb-based mixed-halide (Br-I) perovskite top subcell and a narrower-bandgap (1.25 - 1.55 eV) bottom subcell based on Pb-based or mixed Pb-Sn iodide perovskites. Varying the halide perovskite composition for each subcell enables us to tailor the photovoltaic performance of the tandem devices. We demonstrate that perovskite/perovskite tandem solar cells can deliver open-circuit voltages of more than 2 V. The high photovoltage provides a sufficient overpotential to drive unassisted photoelectrochemical (PEC) water splitting with a solar-to-hydrogen conversion efficiency of more than 15%. After applying water-impermeable encapsulants, the perovskite/perovskite photoelectrodes can successfully operate in an aqueous environment and enable a long operational lifetime.

Comparison of Pb-based and Sn-based perovskite solar cells using SCAPS simulation: optimal efficiency of eco-friendly CsSnI3 devices.

In this study, we employed the one-dimensional solar cell capacitance simulator (SCAPS-1D) software to optimize the performance of Pb-based and Sn-based (Pb-free) all-inorganic perovskites (AIPs) and organic-inorganic perovskites (OIPs) in perovskite solar cell (PSC) structures. Due to the higher stability of AIPs, the performance of PSCs incorporating Cs-based perovskites was compared with that of FA-based perovskites, which are more stable than their MA-based counterparts. The impact of AIPs such as CsPbCl3, CsPbBr3, CsPbI3, CsSnCl3, CsSnBr3, and CsSnI3, as well as including FAPbCl3, FAPbBr3, FAPbI3, FASnCl3, FASnBr3, and FASnI3, was investigated. SnO2 and Cu2O were selected as an inorganic electron transport layer (ETL) and a hole transport layer (HTL), respectively. CsSnBr₃, CsSnI₃, FASnCl₃, and FASnBr₃ exhibited higher efficiency compared to their Pb-based counterparts. Additionally, most Cs-based perovskites, excluding CsPbI₃, demonstrated better performance relative to their FA counterparts. CsSnI3 AIP device also shows the highest short circuit current density (JSC) of 32.85mA/cm2, the best power conversion efficiency (PCE) of 16.00%, and the least recombination at the SnO2/CsSnI3 interface. The thickness, doping, and total defect density of CsSnI3 PSC have been systematically investigated and optimized to obtain the PCE of 17.36%. These findings highlight the potential of CsSnI3 PSCs as efficient and environmentally friendly PSCs.

Low-temperature fabrication of lead-free Ag2BiI5 perovskite photodetector with excellent weak light detection ability for accurate gesture recognition

In recent years, lead halide perovskites have been extensively researched in the optoelectronics field due to their excellent optical and electrical properties, while the inherent toxicity and instability of lead halide perovskites have hindered their commercialization. Stable, lead-free perovskites as a substitute of the Pb-based perovskites show great attention. Herein, the green antisolvent diethyl carbonate is introduced to realize the low-temperature fabrication of nontoxic perovskite Ag2BiI5. The Ag2BiI5 perovskite photodetector (PD) shows excellent performance with a detectivity of as high as 1.13 × 1013 Jones and a linear dynamic range (LDR) of 147 dB. Besides, the weak light with the light intensity of as low as 18.3 nW/cm2 can be detected by our PD. Moreover, the flexible PDs are also prepared with this low-temperature process, which shows good device performance with stable bending resistance characteristics. Based on the excellent optoelectronic properties of the Ag2BiI5 PDs, a gesture recognition system is built which can realize rapid and accurate gesture recognition under ordinary indoor light, with an accuracy of 98.35 %. Our research provides new insights for the development and application of green and environmentally friendly perovskite PD.

Ascorbic acid-induced porous iodide layer for a high-purity two-step solution-processed tin-lead mixed perovskite photodetector

Tin (Sn)-lead (Pb) mixed halide perovskites have attracted widespread interest due to their wider response wavelength and lower toxicity than lead halide perovskites. Among the preparation methods, the two-step method more easily controls the crystallization rate and is suitable for preparing large-area perovskite devices. However, the residual low-conductivity iodide layer in the two-step method can affect carrier transport and device stability, and the different crystallization rates of Sn- and Pb-based perovskites may result in poor film quality. Therefore, Sn-Pb mixed perovskites are mainly prepared by a one-step method. Herein, a MAPb0.5Sn0.5I3-based self-powered photodetector without a hole transport layer is fabricated by a two-step method. By adjusting the concentration of the ascorbic acid (AA) additive, the final perovskite film exhibited a pure phase without residues, and the optimal device exhibited a high responsivity (0.276 A W−1), large specific detectivity (2.38 × 1012 Jones), and enhanced stability. This enhancement is mainly attributed to the inhibition of Sn2+ oxidation, the control of crystal growth, and the sufficient reaction between organic ammonium salts and bottom halides due to the AA-induced pore structure.

An inclusive study of lead-free perovskite CsMI3 materials for photovoltaic and optoelectronic appliance explored by a first principles study

The prime objective of this study is to understand the lead-free CsMI3 (M = Pb, Mg, Ga, Ca, Ba, Sr) perovskites for photovoltaic and optoelectronic applications using first-principle calculations. This study considered the structural aspects along with the mechanical, electrical, optical, and thermal properties. The formation energy, phonon dispersion curve, and elastic constants were calculated to check the structural stability of the compounds. The computed Poisson ratios (ν) support the CsMI3 compounds' ductility; only the CsMgI3 compounds lie on the ductile-brittle transition line. However, the compounds' ductility is confirmed by the Cauchy pressure, which also reflects the materials' mechanism of mechanical failure. The band structure calculations confirmed the energy band gap, Eg, in the range of 1.63–3.26 eV, which makes them suitable for absorbing materials in solar cell applications. The optical properties calculations revealed strong photoconductivity, low reflectivity, and high absorption coefficient, all of which show photovoltaic properties given the materials use in the solar cell application. Among the titled compounds, CsMgI3 will be the best replacement of Pb-based perovskites for photovoltaic and optoelectronic appliances. The substitution of I by Br in the CsMgI3 causes a significant improvement (band gap is increased from 1.12 to 1.87 eV; absorption coefficient is also increased) in the photovoltaic properties. The Eg and α further increase due to doping into the CsMg(I1-xBrx)3 where x = (0.25) makes them apposite for solar cell materials. The best combination, CsMg(I0.75Br0.25)3, shows Eg ∼ 1.4 eV, which may be considered as the optimum band gap for the highest efficiency of a single solar cell according to the Shockley-Queisser limit.

Evaluating Pb-based and Pb-free Halide Perovskites for Solar-Cell Applications: A Simulation Study

Metal halide Pb-based and Pb-free perovskite crystal structures are an essential class of optoelectronic materials due to their significant optoelectronic properties, optical absorption and tuneable emission spectrum properties. However, the most efficient optoelectronic devices were based on the Pb as a monovalent cation, but its toxicity is a significant hurdle for commercial device applications. Thus, replacing the toxic Pb with Pb-free alternatives (such as tin (Sn)) for diverse photovoltaic and optoelectronic applications is essential. Moreover, replacing the volatile methylammonium (MA) with cesium (Cs) leads to the development of an efficient perovskite absorber layer with improved optical & thermal stability and stabilized photoconversion efficiency. This paper discusses the correlation between the experimental and theoretical work for the Pb-based and Pb-free perovskites synthesised using the hot-injection method at different temperatures. Here, simulation is also carried out using the help of SCAPS-1D software to study the effect of various parameters of CsSnI3 and CsPbI3 layers on solar cell performance. This experimental and theoretical comparative study of the Hot-injection method synthesised CsPbI3 and CsSnI3 perovskites is rarely investigated for optoelectronic applications.

Highly Efficient Flexible Photodetectors Based on Pb-Free CsBi3I10 Perovskites.

Perovskites have made remarkable advancements in optoelectronics owing to their high light absorption coefficient, tunable bandgap, and long charge diffusion. Nonetheless, the practical applications of Pb-based perovskites have been hindered by the instability and toxicity of Pb, especially in flexible electronics, which require high biosecurity and low toxicity. Hence, the development of stable Pb-free perovskite materials has gained increasing attention. In this study, we synthesized stable CsBi3I10 Pb-free perovskites outside the glovebox and improved the optoelectronic and mechanical performances of the CsBi3I10-based flexible devices through polyvinylcarbazole (PVK) doping. Flexible photodetectors with the device structure of PET/ITO/PEDOT:PSS/CsBi3I10:PVK/Au was fabricated. The results indicated that the introduction of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) reduced the surface roughness of the flexible PET substrate, while PVK doping further improved the surface smoothness of CsBi3I10 thin films, thereby enhancing the interfacial charge transportation. Moreover, PEDOT:PSS and PVK acted as stepwise hole transport layers in the photodetectors. The device demonstrated a maximum responsivity of 0.3 A/W, detectivity of 2.6 × 1011 Jones, and a response time of 102 μs at 650 nm. After subjecting it to 1000 bending tests, the light current retained 80% of its initial value. This study presents a universally applicable method for controlling the surface morphology of a flexible perovskite thin film.

Bismuth (Bi3+) based lead-free halide perovskitoid for light driven applications: A potential low-toxic alternative for lead (Pb2+)

Bismuth-based perovskite-like materials are recognised as feasible optoelectronic alternatives to lead-based perovskites. High toxicity and limited environmental stability of Pb-based perovskite are the principal hurdles for their practical use, whereas Bismuth (Bi3+) based materials exhibit relatively low toxicity. In this study, we fabricated (FPEA)BiI4 (FPEA = Fluorophenylethyl amine, as a hydrophobic aromatic spacer) and explored its compatibility in the field of photocatalysis and solar cells. UV–Vis, photoluminescence (PL) and time-correlated single photon counting (TCSPC) techniques were used to understand the optoelectronic properties of the material. These fabricated thin films were used towards toxic MBT remediation. Solar cells (in n-i-p configuration) were also fabricated using (FPEA)BiI4 and their photo conversion efficiency (PCE) was tested under AM1.5 illumination.

Theoretical insights into the electronic and optical properties of lithium-based perovskite for solar cell applications

This study explores the influence of central metals and halide anions on the structural, electronic, and optical properties of LiBX3 perovskites (B = Ge, Sn, Pb, X = F, Cl, Br, I) in both unit cell and supercell configurations, aiming for potential applications in photovoltaic devices. Density functional theory calculations reveal that increasing the atomic radius of halogens and central metals directly affects the lattice parameters. Our research indicates that Ge and Sn-based perovskites (except for unit cell LiSnF3) exhibit semiconductor properties with direct band gap energies, while Pb-based perovskites in the unit cell configuration display an indirect band gap. Key factors contributing to the reduction of the band gap energy in most materials include the expansion of the atomic radius of halogens and the examination of perovskites in their supercell state, such that perovskites like LiGeI3, LiSnI3, and LiPbI3 represent a band gap value of 0.001 eV in their supercell configuration. Furthermore, the light absorption characteristics of these perovskites demonstrate a high absorption coefficient ranging from 105 to 106. Among the studied compounds, I-based perovskites exhibit the highest static dielectric constant, surpassing other perovskite variants, with for example, unit cell and supercell of LiSnI3 having static dielectric constant values of 38 and 70, respectively. Additionally, the investigation of perovskites in their supercell form suggests that the number of atoms in the network does not significantly impact their optical properties. In conclusion, based on various analyses, I-based perovskites are proposed as ideal candidates for application in Photovoltaic Solar Cells (PSCs).

High-Efficiency and Ultra-Stable Cesium-Bismuth-Based Lead-free Perovskite Solar Cells without Modification.

Perovskite solar cells (PSCs) have become a new photovoltaic technology with great commercial potential because of their excellent photovoltaic performance. However, the toxicity and poor environmental stability of Pb in Pb-based perovskites limit its large-scale application. Exploring alternatives to Pb is an available approach to develop environmentally friendly PSCs. As an adjacent element of Pb, Bi shows many similar physical and chemical properties; therefore, it is commonly applied for B site substitution in Pb-based PSCs. CsBiSCl2, a new Pb-free perovskite system, was synthesized for the first time as a light absorber. By preparing DMABiS2 as an intermediate, Cs-Bi-based CsBiSCl2 perovskite films with a band gap over 2.012 eV were prepared by introducing CsCl, and the optimal annealing temperature, time, and stoichiometric ratio of the film were explored in this work. The conventional structure of CsBiSCl2 PSCs achieved a power conversion efficiency (PCE) of 10.38%, and the efficiency declined by only 3% after aging in air for 150 days, showing excellent stability, which is one of the most stable devices in inorganic PSCs. This work opens up a new road for the future development of environmentally friendly and commercially stable lead-free PSCs.

Superior Phonon-Limited Exciton Mobility in Lead-Free Two-Dimensional Perovskites.

Tin-based two-dimensional (2D) perovskites are emerging as lead-free alternatives in halide perovskite materials, yet their exciton dynamics and transport remain less understood due to defect scattering. Addressing this, we employed temperature-dependent transient photoluminescence (PL) microscopy to investigate intrinsic exciton transport in three structurally analogous Sn- and Pb-based 2D perovskites. Employing conjugated ligands, we synthesized high-quality crystals with enhanced phase stability at various temperatures. Our results revealed phonon-limited exciton transport in Sn perovskites, with diffusion constants increasing from 0.2 cm2 s-1 at room temperature to 0.6 cm2 s-1 at 40 K, and a narrowing PL line width. Notably, Sn-based perovskites exhibited greater exciton mobility than their Pb-based equivalents, which is attributed to lighter effective masses. Thermally activated optical phonon scattering was observed in Sn-based compounds but was absent in Pb-based materials. These findings, supported by molecular dynamics simulations, demonstrate that the phonon scattering mechanism in Sn-based halide perovskites can be distinct from their Pb counterparts.

Exploring the influence of pressure-induced semiconductor-to-metal transition on the physical properties of cubic perovskites FrXCl3 (X = Ge and Sn)

Even though lead halide perovskites have outstanding physiochemical properties and improved power conversion efficiency, most of these compounds threaten their future commercialization because of their instability and highly toxic nature. Thus, it is preferable to use stable alternative elements rather than lead to make environmentally friendly perovskite material that will have comparable optical and electronic properties to those constructed from Pb-based perovskites. However, devices constructed from lead-free perovskites typically display a lower power conversion efficiency. Applying hydrostatic pressure could be deemed an effective method to alter the physical properties of these compounds. This not only improves their performance in application but also reveals significant correlations between structure and properties. This work uses DFT to investigate the structural, electronic, optical, and elastic properties of non-toxic, francium-based halide perovskites FrXCl3 (X = Ge, Sn) at different levels of hydrostatic pressures that vary from 0 to 10 GPa. The estimated structural parameter's strong correlation with the data from earlier studies ensures the accuracy of the current findings. Pressure causes the Fr−Cl and Ge (Sn)–Cl bonds to shorten and become stronger. The electronic property calculations demonstrated that both compounds are direct band-gap semiconductors. The application of pressure leads to a linear reduction in the band gap (semiconducting to metallic state) and raises the electronic density of states around the Fermi level by forcing the valence band electrons upward, indicating that the optoelectronic device's performance can be tuned and improved. The values of the dielectric constant, absorptivity and reflectivity showed an increasing tendency with pressure. As the pressure applied to the compounds increases, the absorption spectra show a redshift. These findings suggested that the FrXCl3 (X = Ge and Sn) compound becomes more appropriate for usage in optoelectronic applications under pressure. Furthermore, our examination of the mechanical properties indicates that both FrGeCl3 and FrSnCl3 exhibit mechanically stability, and ductility. Interestingly, we observe an increase in ductility as pressure levels rise.