Unique Behavior of Halide Double Perovskites with Mixed Halogens

Theoretical Investigation of the Electronic Property Trends of Antiperovskites with A-site Tetrahedral Cluster Anion

Antiperovskites have garnered significant research interest due to their structural similarity to traditional perovskites and their potential in optoelectronic applications. Recently, their derivatives featuring a combination of tetrahedral and octahedral units within a single antiperovskite lattice have been experimentally synthesized. However, the compositional space of such structural motifs suitable for photovoltaic applications remains largely unexplored. In this study, we perform high-throughput first-principles calculations to screen a series of novel antiperovskite compounds with the general formula X3BA, where the A-site anions are replaced with tetrahedral anion clusters such as (CuCl4)3-, (ZnH3O)3- and (SiO3Cl)3-. Specifically, we evaluate the formability of 60 X3BA compounds, each considered in four competing crystal phases (I4/mcm, P4ncc, Pca21, and Pnma), and systematically analyze the influence of crystal symmetry, tetrahedral cluster anions, and octahedral factors on their electronic structures. Considering geometric factors and electronic band gap criteria, six thermodynamically stable compounds in the I4/mcm phase are identified from 240 candidate structures, including Ca3PCuCl4, Ca3AsCuCl4, Sr3PCuCl4, Sr3AsCuCl4, Ba3PCuCl4, and Ba3AsCuCl4. Among them, Ba3AsCuCl4 stands out as a promising photovoltaic absorber, featuring an optimal HSE06 band gap of 1.55 eV, appropriate carrier effective masses, and strong parity-allowed transitions between band edges at the Γ point. This work expands the structural design paradigm of inorganic solar cell absorbers by simultaneously integrating the core structural motifs of perovskite photovoltaic materials, offering new insights into the development of next-generation photovoltaic absorbers.

The Determination of the Mechanical, Optoelectronic, Structural and Transport Attributes of Double Perovskite A2InGaBr6 (A=K, Rb, Cs) Halides for Renewable Energies: A DFT Study

Safer and more environmentally friendly alternatives to lead-based perovskites include lead-free halide perovskites, which retain good optoelectronic capabilities while reducing environmental toxicity. They also align better with ecological and regulatory standards for green technologies. In this manuscript, we have presented the first principles analysis of the physical traits of A2InGaBr6 (A=K, Rb, Cs). The exchange-correlation effects are treated with mBJ potential. The structural characteristic of A2InGaBr6 (A=K, Rb, Cs) was assessed through the volume optimization curves, formation energies and tolerance factor. The elastic properties of the studied halides are analyzed through elastic constants. The electronic band structures revealed indirect bandgaps for K2InGaBr6, Rb2InGaBr6, and Cs2InGaBr6. The optical properties indicate promising potential in the fabrication of optoelectronic devices for A2InGaBr6 (A=K, Rb, Cs). The transport properties for the studied halides are computed using the BoltzTraP code, which reveals that these halides are promising candidates for thermoelectricity.

Enhancing Optoelectronic Performance of All-Inorganic Double Perovskites via Halogen Doping: Synergistic Screening Strategies and Multiscale Simulations

Designing all-inorganic double perovskites through element mixing is a promising strategy to enhance their optoelectronic performance and structural stability. The complex interplay between multilevel structures and optoelectronic properties in element-mixed double perovskites necessitates further in-depth theoretical exploration. In this study, we employ screening strategies and multiscale simulations combining first-principles methods and device-scale continuum models to identify two novel element-mixed compounds, Rb2AgInCl3I3 and Cs2AgInCl3I3, as promising candidates for photovoltaic applications. These compounds exhibit favorable structural factors and suitable direct band gaps. Theoretical investigations using first-principles methods with the HSE06 functional reveal direct band gaps of 0.98 and 1.26 eV for Rb2AgInCl3I3 and Cs2AgInCl3I3, respectively, with corresponding optical absorption coefficients exceeding 105 cm-1 in the visible light range. Cs2AgInCl3I3 features high charge mobilities of approximately 20 cm2·V-1·s-1 and a notable single-junction spectroscopic limited maximum efficiency (SLME) of 25.54%. Further analysis using the device-scale continuum model simulated the nonradiative recombination effects on power conversion efficiency, integrating quantum-mechanically calculated optoelectronic properties. These theoretical investigations, which bridge composition engineering with multiscale simulations, provide valuable insights into screening novel, lead-free, halogen-mixed double metal perovskite optoelectronic devices, highlighting their potential for high-performance solar energy applications.

Overcoming Intrinsic Quantum Confinement and Ultrafast Self-Trapping in Ag-Bi-I- and Cu-Bi-I-Based 2D Double Perovskites through Electroactive Cations

The possibility to combine organic semiconducting materials with inorganic halide perovskites opens exciting pathways toward tuning optoelectronic properties. Exploring stable and nontoxic, double perovskites as a host for electroactive organic cations to form two-dimensional (2D) hybrid materials is an emerging opportunity to create both functional and lead-free materials for optoelectronic applications. By introducing naphthalene and pyrene moieties into Ag-Bi-I and Cu-Bi-I double perovskite lattices, intrinsic electronic challenges of double perovskites are addressed and the electronic anisotropy of 2D perovskites can be modulated. (POE)4AgBiI8 containing pyrene moieties in the 2D layers was selected from a total of eight new 2D double perovskites, exhibiting a favorable electronic band structure with a type IIb multiple quantum well system based on a layer architecture suitable for out-of-plane conductivity and leading to a photocurrent response ratio of almost 3 orders of magnitude under AM1.5G illumination. Finally, an exclusively parallelly oriented thin film of (POE)4AgBiI8 was integrated into a device to construct the first pure n = 1 Ruddlesden-Popper 2D double perovskite solar cell.

Optoelectronic Properties of Mixed Iodide-Bromide Perovskites from First-Principles Computational Modeling and Experiment

Halogen mixing in lead-halide perovskites is an effective route for tuning the band gap in light emission and multijunction solar cell applications. Here we report the effect of halogen mixing on the optoelectronic properties of lead-halide perovskites from theory and experiment. We applied the virtual crystal approximation within density functional theory, the GW approximation, and the Bethe-Salpeter equation to calculate structural, vibrational, and optoelectronic properties for a series of mixed halide perovskites. We separately perform spectroscopic measurements of these properties and analyze the impact of halogen mixing on quasiparticle band gaps, effective masses, absorption coefficients, charge-carrier mobilities, and exciton binding energies. Our joint theoretical-experimental study demonstrates that iodide-bromide mixed-halide perovskites can be modeled as homovalent alloys, and local structural distortions do not play a significant role for the properties of these mixed species. Our study outlines a general theoretical-experimental framework for future investigations of novel chemically mixed systems.

Critical cation-anion radius ratio and two-dimensional antiferromagnetism in van der Waals TMPS3(TM = Mn, Fe, Ni)

Two-dimensional TMPS₃antiferromagnets, transition metal (TM) = Mn, Fe, Ni, are studied by high-energy x-ray diffraction and atomic pair distribution analysis over a broad temperature range. Results show that the compounds exhibit common average but distinct local atomic structure, including distinct distortions of the constituent TM-S octahedra, magnitude and direction of atomic displacements, TM-TM distances and TM-S-TM bond angles. The differences in the local structure may be rationalized in terms of the Pauling's rule for the critical ratio of TM²⁺cation and S^2-anion radii for octahedral coordination. We argue that the observed differences in the local structure are behind the differences in the antiferromagnetic properties of TMPS₃compounds, including different magnetic anisotropy and Neel temperature.

Origin of bandgap bowing in Cs2Na1-xAgxBiCl6double perovskite solid-state alloys: a paradigm through scanning tunneling spectroscopy

Bandgap bowing has recently been emerged as an effective strategy toward band-engineering in metal halide perovskites. In this work, we report extensive studies on the bowing phenomenon in Cs₂NaBiCl₆double perovskite upon alloying with silver at the sodium site. Through optical spectroscopy, composition-dependent bandgap in Cs₂Na_1-xAg_xBiCl₆(0 ⩽x⩽ 1) evidenced bandgap bowing with an upward-concave nature. Further from the quadratic fit, the bowing coefficient (b= 0.74 eV) turned out to be independent of composition and is close to the theoretically predicted value. From scanning tunneling spectroscopy and associated studies on band-energies, we have observed that the bandgap-lowering originated from a significant change of the valence-band position. The behavior of band-energies has been explained through the orbital-contributions of the constituent elements responsible in forming the two bands. Formation of an internal type-I band-alignment between the two end-members, namely Cs₂NaBiCl₆and Cs₂AgBiCl₆could be visualized. Based on experimental evidences, we could infer that the bow-like evolution of bandgap in Cs₂Na_1-xAg_xBiCl₆alloys is principally dominated by structural distortions in the Cs₂NaBiCl₆host-lattice upon incorporation of silver.

Design of High-Performance Lead-Free Quaternary Antiperovskites for Photovoltaics via Ion Type Inversion and Anion Ordering

The emergence of halide double perovskites significantly increases the compositional space for lead-free and air-stable photovoltaic absorbers compared to halide perovskites. Nevertheless, most halide double perovskites exhibit oversized band gaps (>1.9 eV) or dipole-forbidden optical transition, which are unfavorable for efficient single-junction solar cell applications. The current device performance of halide double perovskite is still inferior to that of lead-based halide perovskites, such as CH₃NH₃PbI₃ (MAPbI₃). Here, by ion type inversion and anion ordering on perovskite lattice sites, two new classes of pnictogen-based quaternary antiperovskites with the formula of X₆B₂AA' and X₆BB'A₂ are designed. Phase stability and tunable band gaps in these quaternary antiperovskites are demonstrated based on first-principles calculations. Further photovoltaic-functionality-directed screening of these materials leads to the discovery of 5 stable compounds (Ca₆N₂AsSb, Ca₆N₂PSb, Sr₆N₂AsSb, Sr₆N₂PSb, and Ca₆NPSb₂) with suitable direct band gaps, small carrier effective masses and low exciton binding energies, and dipole-allowed strong optical absorption, which are favorable properties for a photovoltaic absorber material. The calculated theoretical maximum solar cell efficiencies based on these five compounds are all larger than 29%, comparable to or even higher than that of the MAPbI₃ based solar cell. Our work reveals the huge potential of quaternary antiperovskites in the optoelectronic field and provides a new strategy to design lead-free and air-stable perovskite-based photovoltaic absorber materials.

Identification of Potential Optoelectronic Applications for Metal Thiophosphates

Metal thiophosphates are a large family of compounds that received far less attention than conventional chalcogenides. Recently, however, metal thiophosphates arouse research interest in regard of energy harvesting and conversion due to their structural and chemical diversity. Nevertheless, there remain many unexplored metal thiophosphates. Here, we performed a comprehensive investigation on the electronic and optoelectronic properties of a series of metal thiophosphates using first-principles calculations and identified several highly promising compounds as p-type transparent conductors, photovoltaic absorbers, and single visible-light-driven photocatalysts for water splitting. Our investigation reveals the intrinsic features of a series of typical metal thiophosphates, identifies their new optoelectronic applications, and validates that metal thiophosphates are promising materials deserving exploration.

How the Structures and Properties of Pristine and Anion Vacancy Defective Organic-Inorganic Hybrid Double Perovskites MA2AgIn(BrxI1-x)6 Vary with Br Content x

This work is dedicated to theoretically investigating the mixed-halide direct band gap organic-inorganic hybrid double perovskites (OIHdPs), MA₂AgIn(Br_xI_1-x)₆, with and without anion vacancy point (AVP) defects. We calculate their structural and optoelectronic properties with different halide compositions and find that the effect of halide composition on the properties of MA₂AgIn(Br_xI_1-x)₆ is quite different from that on lead-bearing perovskites. All the vacancy-free I-bearing systems (x ≠ 1) have nearly the same direct band gap width and carrier activity with MAPbI₃. The Br-rich systems (x > 0.50) are relatively thermodynamical stable and not prone to spontaneous anion segregation and show a strong "self-tolerance" feature toward the inherit defects as well. With these distinguished properties, we are able to conclude that MA₂AgIn(Br_xI_1-x)₆ with 0.50 < x < 1 are promising candidates for Pb-free photovoltaic materials. This Letter provides a detailed microscopic understanding of the vacancy-induced band distortion in lead-free heterovalent substitution OIHdPs and has some guiding significance for molecular design of nontoxic photovoltaic materials.