Desirable Optoelectronic Properties Research Articles

Development of MnWO4:Ag nanodilute magnetic semiconductors with tunable magnetic and optoelectronic properties

The bandgap engineered MnWO4 nanoparticles doped with Ag were developed using a facile one-pot synthesis method. The impurity doping concentration of Ag was varied from 1 to 5 wt percentages to tune the interactions between manganese tungstate and silver ions to obtain desirable magnetic and optoelectronic properties. The structural properties of the MnWO4 particles with various concentrations of Ag were investigated using X-ray diffraction. The optical properties of the pristine and Ag-doped MnWO4 particles were determined using UV‒Vis and photoluminescence spectroscopy. The impurity concentration-dependent structural transformations and changes in the vibrational modes, lattice dynamics, electronic transitions and optoelectronic properties of the prepared materials were analyzed using Raman spectroscopy. The topology, morphology and elemental analysis of the synthesized nanoparticles were elucidated using HRTEM, SAED, SEM and EDX techniques. The magnetic properties of the MnWO4:Ag nanoparticles were measured using a vibrating sample magnetometer (VSM). The obtained results suggested that Ag-doped MnWO4 nanosystems show enhanced and tunable magnetic properties suitable for nanodilute magnetic semiconductor (nDMS) applications. The presented work opens a range of possibilities for the development of advanced materials with applications in optoelctronics, nanomedicine, energy-efficient electronic devices and energy conversion.

Synthesis, Structure, and Properties of CuBiSeCl2: A Chalcohalide Material with Low Thermal Conductivity.

Mixed anion halide-chalcogenide materials have recently attracted attention for a variety of applications, owing to their desirable optoelectronic properties. We report the synthesis of a previously unreported mixed-metal chalcohalide material, CuBiSeCl2 (Pnma), accessed through a simple, low-temperature solid-state route. The physical structure is characterized through single-crystal X-ray diffraction and reveals significant Cu displacement within the CuSe2Cl4 octahedra. The electronic structure of CuBiSeCl2 is investigated computationally, which indicates highly anisotropic charge carrier effective masses, and by experimental verification using X-ray photoelectron spectroscopy, which reveals a valence band dominated by Cu orbitals. The band gap is measured to be 1.33(2) eV, a suitable value for solar absorption applications. The electronic and thermal properties, including resistivity, Seebeck coefficient, thermal conductivity, and heat capacity, are also measured, and it is found that CuBiSeCl2 exhibits a low room temperature thermal conductivity of 0.27(4) W K-1 m-1, realized through modifications to the phonon landscape through increased bonding anisotropy.

Zero-dimensional organic-inorganic hybrid cuprous halide of (C20H20OP)CuCl2 with high anti-water stability

Recently, copper(I)-based metal halides have gained increasing attention due to their diverse structures and desirable optoelectronic properties. Herein, we report a novel zero-dimensional (0D) Cu-based halide (C20H20OP)CuCl2 [C20H20OP+ = (Methoxymethyl)triphenylphosphonium chloride cation], single crystals (SCs) of which were synthesized by a simple solution growth method. The bulk assembly of the periodic 0D structure is formed by the organic cation [C20H20OP]+ surrounding isolated [CuCl2]- units. The (C20H20OP)CuCl2 single crystals emit broadband yellow light upon UV excitation. Similarity to hybrid Br−/I− based copper compounds, as-synthesized compound displays remarkable resistance to water, maintaining its photoluminescence (PL) intensity at over 94% even after being immersed in water for 24 h. This work demonstrates the potential of constructing luminescent materials with high water resistance, which will pave the way for a new approach to developing water-resistant materials based on lead-free metal halides.

Comprehensive synthesis of Ti3C2Tx from MAX phase to MXene.

MXenes are a large family of two-dimensional materials that have attracted attention across many fields due to their desirable optoelectronic, biological, mechanical and chemical properties. There currently exist many synthesis procedures that lead to differences in flake size, defects and surface chemistry, which in turn affect their properties. Herein, we describe the steps to synthesize Ti3C2Tx-the most important and widely used MXene, from a Ti3AlC2 MAX phase precursor. The procedure contains three main sections: synthesis of Ti3AlC2 MAX, wet chemical etching of the MAX in hydrofluoric acid/HCl solution to yield multilayer Ti3C2Tx and its delamination into single-layer flakes. Three delamination options are described; these use LiCl, tertiary amines (tetramethyl ammonium hydroxide/ tetrabutyl ammonium hydroxide) and dimethylsulfoxide respectively. These procedures can be adapted for the synthesis of MXenes beyond Ti3C2Tx. The MAX phase synthesis takes about 1 week, with the etching and delamination each requiring 2 d. This protocol requires users to have experience working with hydrofluoric acid, and it is recommended that users have experience with wet chemistry and centrifugation; characterization techniques such as X-ray diffraction and particle size analysis are also essential for the success of the protocol. While alternative synthesis methods, such as minimally intensive layer delamination, are desirable for certain MXenes (such as Ti2CTx) or specific applications, this protocol aims to standardize the more commonly used hydrofluoric acid/HCl etching method, which produces Ti3C2Tx with minimal concentration of defects and the highest conductivity and serves as a guideline for those working with MXenes for the first time.

Electronic, optical, and thermoelectric properties of vacancy-ordered double perovskite K2SnX6 (X = Cl, Br, I) from first-principle calculations

Abstract The present study explores the structural, optoelectronic, and thermoelectric properties of potassium tin halide vacancy-ordered double perovskites K2SnX6 (X = Cl, Br, and I) in their stable monoclinic phase. Our study uses first-principles calculations based on density functional theory (DFT). Electronic band structures reveal direct band gaps for K2SnCl6 and K2SnBr6, while K2SnI6 exhibits an indirect band gap. Theoretical computations utilising the modified Becke-Johnson potential (mBJ-GGA) demonstrate that the optical band gaps of K2SnCl6, K2SnBr6, and K2SnI6 decrease in the following order: 2.581 eV, 1.707 eV, and 4.126 eV, respectively. These values render the materials suitable for photovoltaic applications. Analysis of dielectric functions, absorption coefficients, and refractive indices demonstrates their potential as light-absorbing materials. We evaluate the thermoelectric properties, including electronic and lattice thermal conductivities, Seebeck coefficients, and power factors, which lead to favorable thermoelectric performance. The maximum figure of merit (ZT) values of 0.58, 0.69, and 0.50 are achieved for K2SnCl6, K2SnBr6, and K2SnI6, respectively, at 500 K. These findings highlight the potential of these materials for applications in solar cells and thermoelectric devices, emphasising their effectiveness at elevated temperatures.

Linear and Nonlinear Optical Properties of All-cis and All-trans Poly(p-phenylenevinylene).

Poly(p-phenylenevinylene) (PPV) is a staple of the family of conjugated polymers with desirable optoelectronic properties for applications including light-emitting diodes (LEDs) and photovoltaic devices. Although the significant impact of olefin geometry on the steady-state optical properties of PPVs has been extensively studied, PPVs with precise stereochemistry have yet to be investigated using nonlinear optical spectroscopy for quantum sensing, as well as light harvesting for biological applications. Herein, we report our investigation of the influence of olefin stereochemistry on both linear and nonlinear optical properties through the synthesis of all-cis and all-trans PPV copolymers. We performed two-photon absorption (TPA) using a classical and entangled light source and compared both classical TPA and entangled two-photon absorption (ETPA) cross sections of these stereodefined PPVs. Whereas the TPA cross section of the all-trans PPV was expectedly higher than that of all-cis PPV, presumably because of the larger transition dipole moment, the opposite trend was measured via ETPA, with the all-cis PPV exhibiting the highest ETPA cross section. DFT calculations suggest that this difference might stem from the interaction of entangled photons with lower-lying electronic states in the all-cis PPV variant. Additionally, we explored the photoinduced processes for both cis and trans PPVs through time-resolved fluorescence upconversion and femtosecond transient absorption techniques. This study revealed that the sensitivity of PPVs in two-photon absorption varies with classical versus quantum light and can be modulated through the control of the geometry of the repeating alkenes, which is a key stepping stone toward their use in quantum sensing, bioimaging, and the design of polymer-based light-harvesting systems.

Supramolecular complexation of C60 with branched polyethylene.

Fullerene C60 is a ubiquitous material for application in organic electronics and nanotechnology, due to its desirable optoelectronic properties including good molecular orbital alignment with electron-rich donor materials, as well as high and isotropic charge carrier mobility. However, C60 possesses two limitations that hinder its integration into large-scale devices: (1) poor solubility in common organic solvents leading to expensive device processing, and (2) poor optical absorbance in the visible portion of the spectrum. Covalent functionalization has long been the standard for introducing structural tunability into molecular design, but non-covalent interactions have emerged as an alternative strategy to tailor C60-based materials, offering a versatile and tuneable alternative to novel functional materials and applications. In this work, we report a straightforward non-covalent functionalization of C60 with a branched polyethylene (BPE), which occurs spontaneously in dilute chloroform solution under ambient conditions. A detailed characterization strategy, based on UV-vis spectroscopy and size-exclusion chromatography was performed to verify and investigate the structure of the C60+BPE complex. Among others, our work reveals that the supramolecular complex has an order of magnitude higher molecular weight than its C60 and BPE constituents and points towards oxidation as the driving force behind complexation. The C60+BPE complex also possesses significantly broadened optical absorbance compared to unfunctionalized C60, extending further into the visible portion of the spectrum. This non-covalent approach presents an inexpensive route to address the shortcomings of C60 for electronic applications, situating the C60+BPE complex as a promising candidate for further investigation in organic electronic devices.

Structural tailoring via end-capped acceptors of thiophene-based C-shaped non-fullerene compounds with A-π-A backbone for the exploration of photovoltaic response

In the current era, non-fullerene based electron acceptors show remarkable contribution to develop organic solar cells (OSCs) with maximum possible efficiency via improving their optoelectronic properties. Thus, in current report, eight novel A-π-A type dithieno[3,2-b:2′,3′-d]thiophene (DTh) core-based C-shaped non-fullerene acceptors (ETMM1–ETMM8) were designed theoretically by taking ETMMR as reference to achieve highly proficient photovoltaic materials. Hence, a comprehensive density functional theory (DFT) analysis was accomplished by employing B3LYP level in conjunction with 6-311G(d,p) basis set to determine the enhancement of optical as well as photochemical response. Whereas time-dependent density functional theory (TD-DFT) approach was used for excited state calculations of all the investigated chromophores (ETMMR and ETMM1–ETMM8). So, the influence of structural tailoring via end-capped acceptors modifications was explored by utilizing various quantum chemical analyses such as: transition density matrix (TDM), HOMO–LUMO band gap, density of states (DOS), UV–Vis, binding energy (Eb), global reactivity parameters (GRPs), molecular electrostatic potential (MEP) and open circuit voltage (Voc). Remarkably, all the derivatives (ETMM1–ETMM8) exhibited comparable results with that of the reference chromophore (ETMMR). The results of UV–Vis analysis in chloroform solvent fall in the following order for all the modified chromophores: ETMM5 > ETMM3 > ETMM8 > ETMM4 > ETMM7 > ETMM2 > ETMM6 > ETMM1, which demonstrated maximum red shift in ETMM5 (785.257 eV). Fascinatingly, lowest excitation energy (1.579 eV) as well as binding energy (0.319 eV) along with minimum HOMO/LUMO band gap (1.898 eV) suggested ETMM5 as an excellent candidate for high performance OSCs. Concludingly, all the results indicated that modification of end-capped acceptors is an effective alternative approach to obtain desirable optoelectronic properties.

Synthesis of Ternary and Quaternary Group III-Arsenide Colloidal Quantum Dots via High-Temperature Cation Exchange in Molten Salts: The Importance of Molten Salt Speciation.

Colloidal semiconductor nanocrystals are an important class of materials which have many desirable optoelectronic properties. In their bulk phases, gallium- and aluminum-containing III-V materials such as GaAs, GaP, and Al1-xGaxAs represent some of the most technologically important semiconductors. However, their colloidal synthesis by traditional methods is difficult due to the high temperatures needed to crystallize these highly covalent materials and the extreme reactivity of Ga- and Al- precursors toward organic solvents at such high temperatures. A recently developed paradigm shift in the synthesis of these materials is to use molten inorganic salts as solvents to prepare Ga- containing III-V colloidal nanocrystals by cation exchange of the corresponding indium pnictide (InPn) colloidal nanocrystals. There have been several successful applications of molten salt solvents to prepare III-phosphide colloidal nanocrystals. However, little is known about the nature of these reaction environments at the relevant reaction conditions and synthesis of III-arsenide colloidal nanocrystals remains challenging. Herein we report a detailed study on cation exchange of InPn nanocrystals using nominally Lewis basic molten salt solvents with added gallium halides. Surprisingly, these salt systems phase separate into two immiscible phases, and the nanocrystals preferentially segregate to one of the phases. Using a suite of in situ spectroscopy tools, we identify the phase the nanocrystals segregate to as Lewis neutral alkali tetrahalogallate molten salts. We apply in situ high-temperature Raman spectroscopy to identify the chemical species present in several molten salt compositions at experimentally relevant reaction conditions to elucidate a molecular basis for the reactivity observed. We then employ Lewis neutral KGaI4 molten salts to prepare high-quality In1-xGaxAs and In1-xGaxP nanocrystals and demonstrate that deviation from Lewis neutral conditions accelerate nanocrystal decomposition in the case of III-arsenide materials. Further, we expand to KAlI4-based molten salts to prepare In1-x-yGaxAlyAs nanocrystals which represent an example of solution-synthesized quaternary III-V nanocrystals. These insights provide a molecular basis for the rational development of molten salt solvents, thus allowing the preparation of a diverse array of multicomponent III-V colloidal nanocrystals.

Comprehensive structural and surface investigation of Sb2Se3 thin-films

Earth-abundant antimony selenide (Sb2Se3) is a promising material for the thin-film photovoltaic applications due to its desirable optoelectronic properties and suitable band gap. In this work, we present a comprehensive study on the structural and surface properties of Sb2Se3 thin-films for the potential applications in solar cells. The Sb2Se3 samples were grown on Si (100) substrate and at different substrate temperatures using radio frequency (RF) magnetron sputtering. The XRD diffractogram exhibits that Sb2Se3 is the predominant phase in all the samples, whereas the TEM measurements confirm the nanocrystalline nature of the samples. Raman spectroscopy measurements in the range of 30–500 cm−1 displays the Raman shifts at 148, 190 and 206 cm−1, which confirms the presence of the Sb2Se3 phase. The average surface roughness and grain size were obtained via surface topography with the help of the high-resolution AFM images. The EDS spectra revealed the presence of both Se and Sb as constituent elements in all the samples. The deconvolution of XPS spectra of Se 3p and Sb 3d core level disclose the Sb+3 and Se−2 oxidation state and further confirms the presence of Sb2Se3 phase. The XPS and EDS measurements predict that there is loss of Se during the deposition and it could have adverse effects on the performance of Sb2Se3 solar cell devices.

Density functional theory study of adsorption of organic molecules on ZnO monolayers: Implications for conduction type and electrical characteristics

Graphene-like ZnO monolayer, a typical two-dimensional material, has garnered enormous research attention due to its desirable optoelectronic properties and potential broad applications. However, the difficult in fabricating p-type ZnO material is still undergoing. Herein, the atomic and electronic properties of the adsorption of the selected organic molecules including electrophilic molecule tetracyano-p-quinodimethane (TCNQ) and nucleophilic molecule tetrathiafulvalene (TTF) on ZnO monolayers are carried out by the first-principles calculations. The results indicate that the adsorption of TCNQ on the ZnO monolayer leads to typical p-type doping, with a small gap (Ep) between the lowest unoccupied molecular and the valance band maximum with shallow acceptor states in the middle gap. However, the adsorption of TTF can obtain n-type doping of ZnO monolayer with the large gap (En) between the highest occupied molecular and the conduction band minimum with deep donor states. For TCNQ-ZnO monolayer, it exhibits the enhancement absorb in solar energy. There is a considerable charge transfer and strong non-covalent interaction between TCNQ and ZnO monolayer. The work function of TCNQ-ZnO ML is higher than that of pristine ZnO ML. However, the adsorption of TTF can significantly reduce the work function of ZnO ML, turning it into an n-type conduction semiconductor. Additionally, upon the adsorption of organic molecules, the layer thickness and the interlayer coupling as well as the adsorption concentration can modify the band gap of ZnO, and further tune the conduction type of ZnO. Remarkably, applying electric field can alter the number of hole and further greatly tune the electrical characteristic of TCNQ-ZnO ML. The current results can promote the applications of two-dimensional ZnO in nanoelectronics and optoelectronics.

High‐Performance Blue Perovskite Films and Micro‐Arrays for Light‐Emitting Diodes with Ionic Liquid Interlayer

AbstractMetal halide perovskites have attracted considerable attention for light‐emitting diode (LED) applications due to their desirable optoelectronic properties including high brightness and color purity. However, the performance of blue perovskite LEDs (PeLEDs) remains inferior to their red and green counterparts. Herein, an ionic liquid (IL), specifically 1‐butyl‐3‐methylimidazolium tetrafluoroborate is introduced as the interlayer on the hole transport layer (HTL). This IL demonstrates a strong interaction with the perovskite emissive layer, resulting in effective defect passivation and a shallower valence band maximum. Consequently, nonradiative recombination is reduced, and hole injection is enhanced. Additionally, a soft lithography method employing a transfer process is successfully developed that enables precise micropatterning of the perovskite light‐emitting layer. Through these advancements, the IL‐modified PeLED exhibits pure blue emission at 470 nm with a maximum luminance of 891 cd m−2 and an impressive maximum EQE of 8.3%. Furthermore, the micro PeLED with an IL interlayer achieves a maximum luminance of 400 cd m−2 and a maximum EQE of 3.9%.

Facet-Dependent Photoelectrochemistry on Single Crystal Organic-Inorganic Halide Perovskite Electrodes.

Organometallic halide perovskites have garnered significant attention in various fields of material science, particularly solar energy conversion, due to their desirable optoelectronic properties and compatibility with scalable fabrication techniques. It is often unclear, however, how carrier generation and transport within complex polycrystalline films are influenced by variations in local structure. Elucidating how distinct structural motifs within these heterogeneous systems affect behavior could help guide the continued improvement of perovskite-based solar cells. Here, we present studies applying scanning electron microscopy (SECCM) to map solar energy harvesting within well-defined model systems of organometallic halide perovskites. Methylammonium lead bromide (MAPbBr3) single crystals were prepared via a low-temperature solution-based route, and their photoelectrochemical properties were mapped via SECCM using p-benzoquinone (BQ) in dichloromethane as a redox mediator. Correlated SECCM mapping and electron microscopy studies enabled facet-to-facet variations in photoelectrochemical performance to be revealed and carrier transport lengths to be evaluated. The photoelectrochemical behavior observed within individual single crystals was quite heterogeneous, attributable to local variations in crystal structure/orientations, intrafacet junctions, and the presence of other structural defects. These observations underscore the significance of controlling the microstructure of single perovskite crystals, presenting a promising avenue for further enhancement of perovskite-based solar cells.

Composition-Defined Optical Properties and the Direct-to-Indirect Transition in Core-Shell In1-xGaxP/ZnS Colloidal Quantum Dots.

Semiconductors are commonly divided into materials with direct or indirect band gaps based on the relative positions of the top of the valence band and the bottom of the conduction band in crystal momentum (k) space. It has, however, been debated if k is a useful quantum number to describe the band structure in quantum-confined nanocrystalline systems, which blur the distinction between direct and indirect gap semiconductors. In bulk III-V semiconductor alloys like In1-xGaxP, the band structure can be tuned continuously from the direct- to indirect-gap by changing the value of x. The effect of strong quantum confinement on the direct-to-indirect transition in this system has yet to be established because high-quality colloidal nanocrystal samples have remained inaccessible. Herein, we report one of the first systematic studies of ternary III-V nanocrystals by utilizing an optimized molten-salt In-to-Ga cation exchange protocol to yield bright In1-xGaxP/ZnS core-shell particles with photoluminescence quantum yields exceeding 80%. We performed two-dimensional solid-state NMR studies to assess the alloy homogeneity and the extent of surface oxidation in In1-xGaxP cores. The radiative decay lifetime for In1-xGaxP/ZnS monotonically increases with higher gallium content. Transient absorption studies on In1-xGaxP/ZnS nanocrystals demonstrate signatures of direct- and indirect-like behavior based on the presence or absence, respectively, of excitonic bleach features. Atomistic electronic structure calculations based on the semi-empirical pseudopotential model are used to calculate absorption spectra and radiative lifetimes and evaluate band-edge degeneracy; the resulting calculated electronic properties are consistent with experimental observations. By studying photoluminescence characteristics at elevated temperatures, we demonstrate that a reduced lattice mismatch at the III-V/II-VI core-shell interface can enhance the thermal stability of emission. These insights establish cation exchange in molten inorganic salts as a viable synthetic route to nontoxic, high-quality In1-xGaxP/ZnS QD emitters with desirable optoelectronic properties.

Relating Structure to Properties in Non-Conjugated Pendant Electroactive Polymers.

Non-conjugated pendant electroactive polymers (NCPEPs) are an emerging class of polymers that offer the potential of combining the desirable optoelectronic properties of conjugated polymers with the superior synthetic methodologies and stability of traditional non-conjugated polymers. Despite an increasing number of studies focused on NCPEPs, particularly on understanding fundamental structure-property relationships, no attempts have been made to provide an overview on established relationships to date. This review showcases selected reports on NCPEP homopolymers and copolymers that demonstrate how optical, electronic, and physical properties of the polymers are affected by tuning of key structural variables such as the chemical structure of the polymer backbone, molecular weight, tacticity, spacer length, the nature of the pendant group, and in the case of copolymers the ratios between different comonomers and between individual polymer blocks. Correlation of structural features with improved π-stacking and enhanced charge carrier mobility serve as the primary figures of merit in evaluating impact on NCPEP properties. While this review is not intended to serve as a comprehensive summary of all reports on tuning of structural parameters in NCPEPs, it highlights relevant established structure-property relationships that can serve as a guideline for more targeted design of novel NCPEPs in the future.

Origin of Phase Transitions in Inorganic Lead Halide Perovskites: Interplay between Harmonic and Anharmonic Vibrations

Inorganic lead halide perovskites (ILHPs) exhibit a series of phase transitions, and stabilization of the phases with desirable optoelectronic properties remains a major challenge. However, the intrinsic origins of structural instabilities in CsPbX3 (X = Br, I) are still elusive. Herein, the important role of harmonic and anharmonic vibrations in influencing thermodynamic fluctuations of ILHPs was revealed, through combined lattice dynamics and multiphonon theory calculations, and verified by diffraction experiments. Our results demonstrate that the transition between δ- and γ-CsPbI3 is driven by harmonic vibrations, unveiling the mysterious mechanism for stabilizing γ-CsPbI3 via applying strain. Moreover, the successive transitions from the α- to β- and β- to γ-phases of CsPbX3 are driven by anharmonic vibrations. These structural dynamics are strongly coherent with the phonon diffuse scattering, substantially affecting the thermal conductivity and carrier relaxation. This work provides guidelines for maintaining favorable ILHP phases through delicately manipulating their lattice dynamics.

Quantum Chemistry Insight into the Multifaceted Structural Properties of Two-Dimensional Covalent Organic Frameworks

2D covalent organic frameworks (COFs) possess a wide range of desirable mechanical and optoelectronic properties, rendering them a versatile compound class that is widely investigated in many areas of chemistry. However, experimental structure determination remains challenging as mostly inseparable isomers are measured while computational models mostly account for a very limited number of model structures, making the establishment of comprehensive structure–property relationships difficult. Thus, here, we go computationally beyond the conventional but insufficient description of eclipsed stacked COF building blocks. We emphasize the presence of a variety of stacking and structural motifs and investigate their impact on the electronic properties. Given the very large size of the investigated systems, we employ the fast and accurate tight-binding based semiempirical quantum mechanical (SQM) GFN-xTB method. Taking an imine-linked COF as a representative system, we discuss our structural, energetic, electronic, and spectroscopic results calculated at the periodic GFN1-xTB quantum chemistry level in comparison to experimental findings.

Light-Induced Transient Lattice Dynamics and Metastable Phase Transition in CH3NH3PbI3 Nanocrystals.

Methylammonium lead iodide (MAPbI3) perovskite nanocrystals (NCs) offer desirable optoelectronic properties with prospective utility in photovoltaics, lasers, and light-emitting diodes (LEDs). Structural rearrangements of MAPbI3 in response to photoexcitation, such as lattice distortions and phase transitions, are of particular interest, as these engender long carrier lifetime and bolster carrier diffusion. Here, we use variable temperature X-ray diffraction (XRD) and synchrotron-based transient X-ray diffraction (TRXRD) to investigate lattice response following ultrafast optical excitation. MAPbI3 NCs are found to slowly undergo a phase transition from the tetragonal to a pseudocubic phase over the course of 1 ns under 0.02-4.18 mJ/cm2 fluence photoexcitation, with apparent nonthermal lattice distortions attributed to polaron formation. Lattice recovery exceeds time scales expected for both carrier recombination and thermal dissipation, indicating meta-stability likely due to the proximal phase transition, with symmetry-breaking along equatorial and axial directions. These findings are relevant for fundamental understanding and applications of structure-function properties.

First-principles calculations to investigate structure and fundamental physical properties of BaM2As2 (M = Mg, Zn, Cd) and their alloys

The energetic stability, elastic parameters, electronic structures, effective masses, and optical properties of BaM2As2 (M = Mg, Zn, Cd) and their alloys are revealed for the first time. The results show that it is preferred to adopt the trigonal phase for BaMg2As2 and BaCd2As2, while it may have an additional stable trigonal phase for BaZn2As2 except for the reported experimental phases. The dynamical stability is identified for four novel compounds. The important elastic properties are examined for these compounds and the mechanical stability is confirmed. The band gap energy is greatly narrowed from BaMg2As2 (1.64 eV) to BaCd2As2 (0.80 eV). It is found for BaZn2As2 that the electronic properties of three phases are different from each other. Besides, the band gap calculations can agree with the available experimental results. The bandgap transition behavior is disclosed for three alloys, and their optoelectronic properties are concerned. Both Ba(Mg0.5Zn0.5)2As2 and Ba(Mg0.5Cd0.5)2As2 show the desirable optoelectronic properties including the direct band gap, smaller effective masses, lower exciton binding energy, and high absorption coefficient. The findings are expected to be helpful for discovering novel stable inorganic compounds for potential photovoltaic applications.

Hole-Transporting Self-Assembled Monolayer Enables Efficient Single-Crystal Perovskite Solar Cells with Enhanced Stability

The difficulty of growing perovskite single crystals in configurations suitable for efficient photovoltaic devices has hampered their exploration as solar cell materials, despite their potential to advance perovskite photovoltaic technology beyond polycrystalline films through markedly lower defect densities and desirable optoelectronic properties. While polycrystalline film absorbers can be deposited on myriad substrates, perovskite single crystals fit for high-efficiency devices have only been demonstrated on hydrophobic hole-transport layers [HTLs, e.g., poly(triaryl amine) (PTAA)], which has severely restricted the avenues for enhancing device efficiency and stability. Herein, we report the growth of mixed-cation FA0.6MA0.4PbI3 perovskite single crystals on a hydrophilic self-assembled monolayer {SAM, [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid), (MeO-2PACz)} HTL surface. Compared with PTAA, the MeO-2PACz SAM promotes the mechanical adhesion of the perovskite on the substrate, enabling the fabrication of inverted solar cells with substantially enhanced operational stability and power conversion efficiencies of up to 23.1%, setting a new benchmark for single-crystal perovskite solar cells.