Lead-free Halide Double Perovskites Research Articles

Lead-Free Halide Double Perovskites for Sustainable Environmental Applications

The development of renewable energy sources has become a crucial objective in today's world due to increasing environmental concerns and the depletion of fossil fuels. Solar energy has emerged as a promising alternative. In recent years, there has been a significant focus on perovskite solar cells due to their remarkable power conversion efficiencies and their ability to be produced in a cost-effective manner. These cells have attracted considerable attention from researchers and industry professionals alike. However, traditional perovskite materials often contain toxic lead, raising concerns about their environmental impact and long-term sustainability. This article highlights the environmental concerns associated with lead-based perovskite materials and explores the advantages, challenges, and potential of lead-free halide double perovskites as sustainable alternatives for achieving an enlightening and sustainable future in the field of photovoltaics. Lead-free halide perovskites have been an area of active research in the field of nanotechnology and material science due to their potential for various applications. We provide an overview of perovskite solar cells as a promising technology, discussing their material properties and device performance. Furthermore, we present a comparative analysis between lead-based and lead-free perovskites, emphasizing the challenges and future perspectives associated with the development and implementation of lead-free alternatives. Through this analysis, we aim to shed light on the potential of lead-free halide double perovskites and inspire further research in the quest for environmentally friendly materials for solar energy applications.

Engineering Cl vacancies in lead-free halide double perovskites decorated on TiO2 nanotubes for highly sensitive NO2 sensing at room temperature

Engineering Cl vacancies in lead-free halide double perovskites decorated on TiO2 nanotubes for highly sensitive NO2 sensing at room temperature

First-principles investigation of Rb2NaXCl6 (X = In, Tl) compounds for energy harvesting applications

Lead free halide double perovskites (HDPs) have attracted significant interest of the scientific community owing to their better stability, low cost, and eco-friendly nature, and high power conversion efficiency for optoelectronic, and thermoelectric usages. Herein, the physical properties of two novel Rb2NaInCl6 and Rb2NaTlCl6 HDPs are reported via first principles methods. Both HDPs are found to be stable thermodynamically and geometrically, supported by negative formation enthalpies, and structural optimization. Electronic properties analysis revealed direct band gap values of 4.88 and 3.13 eV for respective Rb2NaInCl6 and Rb2NaTlCl6 structures. Corresponding to these band gap values, both HDPs are optically active in the ultraviolet (UV) region of light. Static dielectric constant (Ɛ1 (0)) is consistent with Penn's model. Maximum polarization is achieved at 7.1/5.16 eV for Rb2Na(In/Tl)Cl6, respectively. Maximum absorption peaks occurred in UV region, predicting their suitability for high energy optoelectronic applications. The optical conductivity revealed the highest intensity of 3049.72 (at 5.4 eV) for Rb2NaTlCl6 and 2632.08 Ω−1cm−1 (at 7.4 eV) for Rb2NaInCl6. Moreover, our analysis of thermoelectric parameters revealed that Rb2NaInCl6 and Rb2NaTlCl6 have figure of merit (ZT) values of 0.73/0.75, respectively. High ZT values and greater absorption in the UV region suggest that Rb2Na(In/Tl)Cl6 are suitable for TE and optoelectronic usages.

Evidence and engineering of x-ray luminescence in lead free perovskite Cs2AgInCl6 with Bi substitutions

Cs2AgInCl6 belongs to the family of lead-free halide double perovskites. Lead-free halide double perovskite appears as a viable contender for scintillator applications due to its inexpensive production costs, low intrinsic trap density, and nanosecond quick reaction. Perovskite crystals have a substantially lower trap density than lead halide and traditional oxide scintillator materials, according to thermo-luminescence measurements. Cs2AgInCl6 structure and dimensionality were engineered by Bi doping. Bi substitution reduces the bandgap, making it suited for scintillation applications. Bi substitution allows for easy tuning of Cs2AgIn(1−x)BixCl6 (0 ≤ x ≤ 50) due to its wide versatility in scintillation properties. For Cs2AgIn(1−x)BixCl6 (0 ≤ x ≤ 50), x-ray power dependent luminescence increases with increasing power. Because of their nontoxicity, sensitivity, reaction time, and stability, Cs2AgIn(1−x)BixCl6 (0 ≤ x ≤ 50) double perovskite crystals are promising for x-ray scintillation.

Selecting ns2 electron (Sb3+) and d3 electron (Cr3+) co-doped in lead-free halide double perovskite to achieve blue and near-infrared luminescence

The double-perovskite Cs2NaInCl6 has emerged as a highly favored candidate due to its remarkable stability and eco-friendly properties. However, it is noteworthy that this material does not demonstrate the desired optical performance in the crucial visible and near-infrared (NIR) spectrum, which may limit its potential applications in certain domains. We develop such characteristics in Cs2NaInCl6 by co-doping Sb3+ (s-electron) and Cr3+ (d-electron) ions. Doping with Sb3+ allows for 1S0→3P1 transition absorption, which then emits blue photoluminescence of self-trapped exciton (STE). By co-doping Sb3+ and Cr3+ ions, it causes the transfer of excitation energy from STE to Cr3+, yielding strong NIR emission at 950 nm. Temperature-dependent Photoluminescence (PL), PL excitation, PL decay and Tanabe-Sugano diagram provide insight into photophysical processes. Furthermore, a novel dual-modal optical information encryption based on the integration of blue and NIR luminescence printing patterns using Cs2NaInCl6: Sb3+ and Cs2NaInCl6: Sb3+/Cr3+, respectively, is successfully demonstrated.

New semiconducting lead-free halide double perovskite Ag2LiGaF6 for optoelectronic and thermoelectric applications

A comprehensive study of lead-free halide double perovskite using density functional theory (DFT) including structural, electronic, dynamical, mechanical, optical, and thermoelectric properties has been carried out. The tolerance factor and the octahedral factor confirm that the compound belongs to face-centred-cubic structure with Fm-3m space group. The predicted band structure and DOS exhibit that the material is an indirect bandgap semiconductor. Our calculation reveals that material is dynamically stable because of no negative frequency found in phonon-dispersion curve. The material also possesses mechanical stability. The optical spectra of material show good absorbance and low reflectivity in ultraviolet region. The thermoelectric part discusses the Seebeck coefficient, thermal conductivity, electrical conductivity, power factor, and figure of merit (zT) at different chemical potential into temperature range 400–1200 K. The purpose of this investigation is to stimulate researchers to develop this kind of material and assess their potential for the advancement of contemporary thermoelectric and optoelectronic devices.

Mechanism of Pressure-Modulated Self-Trapped Exciton Emission in Cs2TeCl6 Double Perovskite.

Pressure-modulated self-trapped exciton (STE) emission mechanism in all-inorganic lead-free metal halide double perovskites characterized by large Stokes-shifted broadband emission, has attracted much attention across various fields such as optics, optoelectronics, and biomedical sciences. Here, by employing the all-inorganic lead-free metal halide double perovskite Cs2TeCl6 as a paradigm, the authors elucidate that the performance of STE emission can be modulated by pressure, attributable to the pressure-induced evolution of the electronic state (ES). Two ES transitions happen at pressures of 1.6 and 5.8GPa, sequentially. The electronic behaviors of Cs2TeCl6 can be jointly modulated by both pressure and ES transitions. When the pressure reaches 1.6GPa, the Huang-Rhys factor S, indicative of the strength of electron-phonon coupling, attains an optimum value of ≈12.0, correlating with the pressure-induced photoluminescence (PL) intensity of Cs2TeCl6 is 4.8-fold that of its PL intensity under ambient pressure. Through analyzing the pressure-dependent STE dynamic behavioral changes, the authors have revealed the microphysical mechanism underlying the pressure-modulated enhancement and quenching of STE emission in Cs2TeCl6.

Geometric and electronic structures of Cs2BB′X6 double perovskites: The importance of exact exchange

A widely adopted computational protocol in contemporary materials research is to first relax materials' geometries using semilocal density functional approximations (DFA), and then determining their electronic band structures using the more expensive hybrid functionals. This procedure often works well, as the popular semilocal DFAs, such as the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation, yield rather good geometries for a wide range of materials. However, here we show that, for some of the lead-free halide double perovskites (HDPs) Cs2BB′X6 (B=Ag+, Na+; B′=In3+, Bi3+; X=Cl−, Br−), the validity of this common practice is questionable. We find that, for these HDPs, the geometrical structures, in particular, the B(B′)−X bond lengths predicted by PBE show large deviations from the experimental values. Additionally, the band gaps of some of these materials (specifically, the In-based HDPs) are sensitive to the B(B′)−X bond lengths. As a consequence, the band gaps obtained using the hybrid functionals (such as the Heyd-Scuseria-Ernzerhof functional) based on the PBE geometries can still be quite off, in particular, for HDPs with B′=In3+. The situation is significantly improved by using hybrid functionals with tuned portion of exact exchange, based on the geometries determined consistently under the same level of theory. The successes and failures of several popular exchange-correlation (XC) functionals are traced back to the so-called delocalization error, and can be quantitatively analyzed and understood via a three-atom linear-chain B−X−B′ molecular model. Finally, our findings provide a practical guide for choosing appropriate XC functionals for describing HDPs and point to a promising path for band structure engineering via doping and alloying. Published by the American Physical Society 2024

Improving Cs2AgBiBr6 double perovskite solar cells through graphdiyne doping: A Stride towards enhanced performance

Lead-free halide double perovskites (LFHDPs) based on Cs2AgBiBr6 provide a promising replacement for conventional lead-based LBPs, offering significant benefits in terms of non-toxicity and chemical stability. Nevertheless, the efficiency of Cs2AgBiBr6 solar cells is restricted due to their significant bandgap (Eg). The proposed solution involves optimizing the optical and photovoltaic properties of Cs2AgBiBr6 through graphdiyne (GD) doping. The synthesized Cs2Ag0.95GD0.05BiBr6 is extensively characterized by means of X-ray diffraction (XRD), solar simulator studies, and UV–vis spectroscopy. XRD analysis reveals peak position shifts, indicating changes in the crystal structure caused by GD doping. Optical examination indicates a drop in Eg, this results in enhanced light absorption in the visible region. The increased performance of the Cs2Ag0.95GD0.05BiBr6 solar cell is demonstrated by its higher fill factor (FF), open-circuit voltage (Voc), and short-circuit current (Jsc), which are measured at 0.91 V, 5.58 mA-cm−2, and 0.75, respectively. As a result, the power conversion efficiency (PCE) increases to 3.74 % from 3.37 %. Our research not only tackles film formation issues but also develops stable Cs2Ag0.95GD0.05BiBr6 as a high-performance material for solar applications. All in all, our effort promotes solar technology that is environmentally benign. This work develops stable Cs2Ag0.95GD0.05BiBr6 as a high-performance substance that aids in overcoming film forming challenges in solar applications. Overall, our work advances ecologically friendly solar technology.

Synthesis and characterization of novel double perovskite K2AgBiBr6

Over the past few years, Lead-free halide double perovskites have attracted a tremendous attention such that it is demonstrated by the power conversion efficiency's sharp increase of over 25 %. It has also stimulated a widespread application of halide metal perovskites in other fields, such as light-emitting diodes, field-effect transistors, detectors, and lasers. Double perovskites have been put forth as an alternative to hybrid lead halide perovskites in the last decade because of their efficiency in doing away with the existing toxicity and instability. It is probably the first attempt, to date, that lead-free halide double perovskite K2AgBiBr6 has been made with a cheap, easy-to-use solution-state reaction method. To determine their structure, single crystal X-ray diffraction and PXRD analysis have been employed. The synthesized K2AgBiBr6 adopts the cubic structure with Fm‾3m symmetry and lattice parameters of a = 6.606 (9) Å at room temperature, according to the diffraction result. Energy dispersive X-ray spectroscopy (EDX), elemental mapping, and scanning electron microscopy (SEM) have all been employed to analyze the morphology and elemental composition. Elements including K, Bi, Ag, and Br have been confirmed to be present in the synthesized sample by the EDX technique. For K2AgBiBr6, the 2.859 eV (indirect) and 3.076 eV (direct) bandgaps have been estimated by employing the UV–Vis absorption spectra. Furthermore, the K2AgBiBr6 double perovskite nanocrystal's thermogravimetric analysis/differential thermal and differential scanning analysis (TG/DTA and DSC) curves at 20–800 °C have been measured. An analysis has been conducted on the mechanism of thermal decomposition of synthesized double perovskite. This work demonstrates great promise for future band gap engineering-based photovoltaic and other optoelectronic applications, and it offers a novel path to obtaining premium K2AgBiBr6 double perovskite.

Compressive strain-induced enhancement of thermoelectric performance in lead-free halide double perovskites K2SnX6 (X = I, Br, Cl)

Exploring thermoelectric materials with high performance and low cost is of great importance in mitigating environmental and energy challenges. Here, we provide an atomistic insight into strain-induced enhancement of thermoelectric performance in potassium-based halide double perovskite K2SnX6 (X = I, Br, Cl) using first-principles calculations. To get reliable predictions for transport properties, we adopt advanced methods such as self-energy relaxation time approximation for electron transport and unified theory for lattice transport in combination with self-consistent phonon approach. Our calculations highlight a promising thermoelectric figure of merit ZT over 1.01 in K2SnI6 when applying a compressive strain of −6%, being tenfold larger than those in the uncompressed compounds, suggesting that compressing is an effective way to enhance the thermoelectric performance of halide double perovskites.

K2Ag(Ga/In)Br6 lead-free HDPs: Investigation of the elastic, optoelectronic, optical coating, and thermal characteristics for thermoelectric and solar cells

In this study, an investigation of the structural stability, elastic, optoelectronic, thermoelectric, optical thin-film coating, and thermodynamic properties of K2Ag(Ga/In)Br6 (lead-free halide double perovskites, HDPs) was performed using first-principles calculations. The optimized structural parameters are in good agreement with the available data. Furthermore, Goldsmith's tolerance factor indicates an ideal value for both double perovskites, ensuring the structural stability of the cubic perovskites, and the elasticity parameters were analyzed to ensure the mechanical stability of the cubic phase. Direct and reduced band gaps of 0.4524 eV and 1.064 eV with semiconductor behavior are found for K2AgGaBr6 and K2AgInBr6, respectively, through adoption of the modified Becke–Johnson potential scheme. The absorption coefficient, refractive index, and dielectric function, as some of the optical properties, in addition to the optical thin-film properties, are well discussed, and the values suggest that these materials are promising candidates for different devices, such as optoelectronic and photovoltaic energy devices. In terms of the thermodynamics, the HDPs display favorable characteristics across various temperature and pressure ranges. Additionally, we assessed the thermoelectric properties, considering the power factor, Seebeck coefficient, thermal and electronic conductivities, and figure of merit. The current predictions suggest that these lead-free halide double perovskites have strong potential for application in thermoelectricity and photovoltaics.

DFT calculations of new Li-based halides Li2AgAlY6 (Y = Cl, Br, I) for energy conversion applications

Recently, lead-free halide double perovskite (DP) materials have got scholarly attention owing to their environmentally sustainable characteristic, excellent stability and potential applications in solar cells and renewable energy. In this present article, we computationally examined the mechanical, optoelectronic and thermoelectric characteristics of a discernible compound Li2AgAlY6 (Y = Cl, Br, I) using the density functional theory (DFT). The evaluation of tolerance factor (tf), lattice constant (a0), and formation enthalpy (Hf) confirms the structural and thermodynamic stability of the investigated double DPs, also elastic constants further elaborate the mechanically stable nature. The studied compounds have direct band gap of 3.6 eV, 2.6 eV and 1.2 eV for Li2AgAlCl6, Li2AgAlBr6 and Li2AgAlI6 respectively, indicating the diverse energy absorption applications from ultraviolet to visible region. We used semi-classical Boltzman theory to determine the figure of merit (ZT) and corresponding Seebeck Coefficient (S), which validates the electrical and thermoelectric conductivity for the compounds under investigation. The current investigation establishes a theoretical foundation for the examined DPs, essential for comprehending and comparing forthcoming experimental inquiries aimed at exploring diverse optoelectronic and thermoelectric applications.

Boosting the stability of Lead-Free halide double perovskite through encapsulation in COF

Halide perovskite has emerged as a promising candidate for optical applications owing to its exceptional photophysical properties. However, inherited toxicity and instability of the materials against heat, moisture, light, and solvent retard their commercialization. To address this issue, in this work, we report the synthesis of lead-free halide double perovskite composite with the covalent organic framework (COF). Here, COF behaves as a protective layer for perovskite from external stimuli forming a Cs2AgBiCl6@COF composite. The composite maintains its structural integrity when exposed to ambient conditions, elevated temperature for a long time, prolonged UV irradiation, and polar solvent. The composite also remains stable when it is in contact with water. We have performed several characterization techniques to validate the formation and stability of the Cs2AgBiCl6@COF composite in various conditions. Our work is not only removing the toxicity of lead but simultaneously improving the stability of perovskite materials against different environmental conditions.

Comprehensive prediction of lead-free mixed-valence Cs2AgIAuIIIX6 (X = Cl, Br, I) halide double perovskites for high-efficiency photovoltaics

In light of their suitability for optoelectronic and photovoltaic devices, lead-free halide double perovskites (HDPs) have been extensively concerned in recent years. However, most HDPs have large and indirect band gaps (> 2 eV), which is unfavorable for perovskite solar cells. Here, the structural stability, optoelectronic response, and photovoltaic performance of mixed-valence HDPs Cs2AgIAuIIIX6 (X = Cl, Br, I) have been theoretically examined. The thermodynamic, dynamical, and mechanical stability are verified in terms of the decomposition energy, phonon dispersion, and elastic constants. The computed indirect-gaps are 1.44 eV for Cs2AgIAuIIICl6, 1.25 eV for Cs2AgIAuIIIBr6, and 1.22 eV for Cs2AgIAuIIII6, respectively. These mixed-valence Cs2AgIAuIIIX6 (X = Cl, Br, I) HDPs possess more suitable optical band gaps in comparison with that of Cs2AuIAuIIIX6. The role of different metal cations in determining electronic properties is further elucidated. Furthermore, the optical analysis discloses that three mixed-valence HDPs exhibit high visible-light absorption coefficients. Additionally, the photovoltaic response of Cs2AgIAuIIIX6 (X = Br, I) is further substantiated since the predicted efficiency is beyond 28 %. Overall, our study reveals that mixed-valence Cs2AgIAuIIIX6 (X = Cl, Br, I) HDPs shows good stability and superior photovoltaic performance, which is an efficient candidate for single-junction perovskite solar cells.

Temperature-Dependent Photoluminescence from Well-Resolved Excited State Structures in Rare-Earth-Based Double Perovskites.

Lead-free halide double perovskites (DPs) have become a research hotspot in the field of photoelectrons due to their unique optical properties and flexible compositional tuning. However, the reports on the optical properties of DPs primarily concentrate on the room temperature state and only exhibit single emission band. Here, we synthesized Cs2NaYCl6:Sb3+, Dy3+ DPs by a solvothermal method to realize white light emission with photoluminescence (PL) quantum yield as high as 70.7%. The energy-transfer process from self-trapped excitons (STEs) to Dy3+ ions was revealed by optical characterization and theoretical simulation calculations. Interestingly, we observed the double-emission from low-energy STE emission of Sb3+ ions and Dy3+ emission at low temperatures, and the double-emission is consistent with the asymmetric doublet feature of the 3P1 → 1S0 transition split into two minima. The PL spectra further showed that the fluorescence intensity ratios of Dy3+ ions at 580 and 680 nm were strongly temperature-dependent, and the relative sensitivity is up to 1.79% K-1 at 360 K. Moreover, the near-infrared and radiation luminescence properties indicated that the Cs2NaYCl6:Sb3+, Dy3+ DPs also have good prospects for night vision and radiation detection, as well as the great potential for applications in solid-state illumination and optical temperature measurement.

Achieving versatile optoelectronic applications of environment-friendly halide double perovskite by multi-ion codoping strategy

Lead-free halide double perovskites (DPs) have been regarded as a class of environmentally friendly and promising optoelectronic materials. Herein, we report the synthesis, luminescence properties, and optoelectronic applications of lanthanide (Ln = Yb3+/Er3+)/M (M = Bi3+/Sb3+/Mn2+) codoped Cs2NaInCl6 single crystals (SCs). The Yb/Er codoped Cs2NaInCl6 SCs show upconversion and downshifting visible/short-wave infrared (SWIR) photoluminescence emission. After further introduction of Sb3+/Mn2+ ions into the host, bright blue and red emissions are observed with the PLQYs of 96.28% and 21.58%, respectively. With the incorporation of Bi3+ ions, the upconversion and visible/SWIR luminescence intensities of Yb/Er/Bi codoped Cs2NaInCl6 SCs are significantly enhanced. The incorporation of Bi3+ dopant in the DP host can construct a more efficient energy transfer process, resulting in excellent luminescence efficiency. The multi-ion codoped DP system exhibits great potential for optoelectronic applications in the fields of anticounterfeiting, photodetector, and x-ray imaging. This work will help guide the design and development of environmentally friendly multi-functional materials.

Impact of doping and hydrostatic pressure on structural, electronic, optical, and mechanical properties of novel double halide perovskite Cs2LiGaBr6

The emergence of lead-free halide double perovskites exhibiting bandgaps within the visible spectrum represents a substantial advancement in engineering environmentally benign perovskite solar cells. In this work, we investigated the structural, optical, electronic, and mechanical properties of Cs-based lead-free Cs2LiGaBr6 double halide perovskites with Mn and Cr doping under hydrostatic pressure ranging from 2 to 80 GPa using density functional theory (DFT). The introduction of dopants consistently alters the lattice parameters because of the mismatch in atomic radii, whereas increasing the pressure leads to a reduction in these constants. All the studied Cs2LiGaBr6 compounds exhibited direct band gaps, which increased slightly with doping. This is attributed to the modulation of electronic states by dopant-related defect levels. The bandgap variation under pressure is primarily attributed to changes in the quantum confinement effects induced by compressive strain. Analysis of the density of states and optical properties revealed enhanced absorption in the visible spectrum for the doped compositions, and in the UV spectrum under pressure. The study of mechanical stability confirms the ductile nature of both the doped and pristine compounds under pressure, underscoring their suitability for thin film production. This study contributes to the understanding of sustainable alternatives for perovskite optoelectronic applications, emphasizing Cs2LiGaBr6's potential under diverse conditions and dopant influences.

Optoelectronic and thermoelectric response of lead free halide double perovskites Rb2AgPX6 (X = Cl, Br, I) for energy storage applications

Optoelectronic and thermoelectric response of lead free halide double perovskites Rb2AgPX6 (X = Cl, Br, I) for energy storage applications

Tunable multicolor-emission in Eu3+ and Tb3+ codoped Cs2NaInCl6:Sb3+ double perovskite nanocrystals and its dual-model anti-counterfeiting and temperature-sensing applications

Lead-free metal halide double perovskites with non-toxicity and stable self-trapped excitons (STEs) have received considerable attention in the field of photoelectric applications. However, it is difficult to achieve independent control of its photoluminescence performance to meet the requirements of multi-band emission. Herein, a doping strategy was employed to introduce lanthanide ions (Ln3+) into Cs2NaInCl6:Sb3+ nanocrystals (NCs), enabling the multicolor emission modulation ranging from blue to red and even white light. Benefiting from the efficient energy transfer from Sb-related self-trapped excitons to Ln3+ ions, green and red emissions originate from the 5D0→7FJ (J = 1, 2, 3, 4) transition of Eu3+ ions and 5D4-7FJ (J = 6, 5, 4, 3) transition of Tb3+ ions, respectively. According to the tunable polychromatic photoluminescence characteristics of doped NCs, the dual-mode fluorescent anti-counterfeiting applications were exhibited. Furthermore, the distinct temperature sensitivities exhibited by blue (453 nm) and red (617 nm) emission in Cs2NaInCl6:Sb3+/Eu3+ NCs provide the opportunity for the optical thermometry, which demonstrates the maximum absolute and relative sensitivity are 0.0018 and 0.43 % K−1, respectively. These results indicate that the synthesized codoped NCs have the potential applications in multifunctional fields, such as optical thermometer, fluorescence anti-counterfeiting, and multicolor-LEDs.