Optoelectronic Properties Research Articles

Flexible bistable polymer stabilised cholesteric texture light shutter display

ABSTRACT Bistable cholesteric liquid crystal displays meet various needs such as energy saving, long image storage time, and no backlight; however, their dense polymer network affects the electro-optical performance. In this work, polymer-stabilised cholesteric texture (PSCT) films with polymer spacer columns were prepared by two-step polymerisation using photomask. The effects of crosslinker content and mask polymerisation time on the morphology of the polymer spacer columns and the optoelectronic properties of the PSCT films were investigated. The results suggested that the film showed bistable performance and the formation of polymer spacer columns helped to optimize the contrast ratio of the sample without sacrificing response time. The cyclic experiment indicated that the optimized bistable PSCT film showed good stability. The adhesion strength of the PSCT film to the substrate was essentially the same as that of commercial PDLC. The simple operability and reusability of the process method make it a practical solution for the preparation of bistable PSCT films.

Light-induced electron dynamics of molecules in cavities: comparison of model Hamiltonians

The rapidly expanding field of polaritonic chemistry requires accurate theoretical simulations to understand new phenomena at the atomic scale. Computing the optoelectronic properties of molecules using established electronic structure methods is a careful balance of accuracy and computational expense, and expanding these methods to quantum electrodynamics to describe coupled cavity-molecule systems is an active topic of development. Key to these methods are the Hamiltonian operators representing the photon cavity modes. The recently introduced quantum electrodynamics time-dependent configuration interaction (QED-TDCI) method allows for the combination of electron dynamics simulations with quantum electrodynamics, enabling the simulation of time-dependent optoelectronic properties of cavity-molecule systems. Using this method, a comparison of two many-state QED Hamiltonians—the Pauli-Fierz and quantum Rabi model Hamiltonians—is presented, with a particular focus on time-dependent properties in applied electric fields.

Advances in Mixed Tin-Lead Narrow-Bandgap Perovskites for Single-Junction and All-Perovskite Tandem Solar Cells.

Organic-inorganic metal-halide perovskites have received great attention for photovoltaic (PV) applications owing to their superior optoelectronic properties and the unprecedented performance development. For single-junction PV devices, although lead (Pb)-based perovskite solar cells (PSCs) have achieved 26.1% efficiency, the mixed tin-lead (Sn-Pb) perovskites offer more ideal bandgap tuning capability to enable an even higher performance. The Sn-Pb perovskite (with a bandgap tuned to approximately 1.2eV) is also attractive as the bottom subcell for a tandem configuration to further surpass the Shockley-Queisser radiative limit for the single-junction devices. The performance of the all-perovskite tandem solar cells has gained rapid development and achieved a certified efficiency up to 29.1%. In this article, we review the properties and recent development of state-of-the-art mixed Sn-Pb perovskites and their application in single-junction and all-perovskite tandem solar cells. We highlight recent advances in various approaches covering additives, solvents, interfaces, and perovskite growth. We also provide our perspective and outlook on the challenges and strategies for further development of mixed Sn-Pb perovskites in both efficiency and stability for PV applications. This article is protected by copyright. All rights reserved.

Phonon Properties and Lattice Dynamics of Two- and Tri-Layered Lead Iodide Perovskites Comprising Butylammonium and Methylammonium Cations—Temperature-Dependent Raman Studies

Hybrid lead iodide perovskites are promising photovoltaic and light-emitting materials. Extant literature data on the key optoelectronic and luminescent properties of hybrid perovskites indicate that these properties are affected by electron–phonon coupling, the dynamics of the organic cations, and the degree of lattice distortion. We report temperature-dependent Raman studies of BA2MAPb2I7 and BA2MA2Pb3I10 (BA = butylammonium; MA = methylammonium), which undergo two structural phase transitions. Raman data obtained in broad temperature (360–80 K) and wavenumber (1800–10 cm−1) ranges show that ordering of BA+ cations triggers the higher temperature phase transition, whereas freezing of MA+ dynamics occurs below 200 K, leading to the onset of the low-temperature phase transition. This ordering is associated with significant deformation of the inorganic sublattice, as evidenced by changes observed in the lattice mode region. Our results show, therefore, that Raman spectroscopy is a very valuable tool for monitoring the separate dynamics of different organic cations in perovskites, comprising “perovskitizer” and interlayer cations.

Optoelectronic properties of mechanically stable cubic Niobate compounds under hydrostatic pressure: A systematic DFT investigation

Perovskite oxides, particularly cubic Niobate compounds, have been studied for their potential application in the development of optoelectronic devices. The mechanical stability of these compounds has been verified by determining their elastic constants. Based on an analysis of their electronic band structures and densities of states, it has been found that both compounds exhibit non-magnetic behavior and possess properties typical of indirect bandgap semiconductors. The bandgap energies of the compounds are 1.524 eV and 1.392 eV, respectively. The optical properties of the compounds are analyzed under varying hydrostatic pressure conditions. Bandgap modulation results in a shift in absorption spectra from ultraviolet to visible wavelengths, rendering the materials appropriate for use in optoelectronic devices. Perovskites with (K,Rb)NbO3 exhibit potential as non-magnetic indirect bandgap semiconductors for the advancement of optoelectronic devices.

Anisotropic optoelectronic properties of lead-free Cs3Bi2I9 single-crystal photodetectors

Lead-free halide perovskites have attracted widespread research interest due to their excellent optoelectronic properties and environmental friendliness. As one of the bismuth iodide compounds, Cs3Bi2I9 perovskite has been extensively explored in the field of photovoltaic devices and radiation detectors due to their non-toxic lead-free components and excellent stability. In this work, we successfully grow large-sized Cs3Bi2I9 single crystals (SC) with (l00) and (00l) crystal exposure facets by inverse temperature crystallization method. Under 525 nm light illumination with the intensity 15 mW cm−2 and 7 V bias, the (l00) Cs3Bi2I9 SC shows 2 times higher photocurrent, 3.6 times higher responsivity, and 2.8 times higher detectivity than the (00l) Cs3Bi2I9 SC, respectively. Superior response time in the scale of millisecond is obtained in both (l00) and (00l) Cs3Bi2I9 SCs. Based on the first-principle calculation, the (l00) SC possesses a higher charge distribution density and a wider dispersion distribution than (00l) SC, suggesting that more electrons in the (l00) SC can be excited in a wider range. The tighter arrangement of Cs+ and [BiI6]− octahedra in the (l00) SC than (00l) SC leads to the anisotropic photoelectric performance in (l00) and (00l) Cs3Bi2I9 SCs. Our results provide a strategy for the oriental growth of Cs3Bi2I9 SCs and the design of anisotropic optoelectronic devices with excellent performance.

Rational design of comb-like 1D-1D ZnO-ZnSe heterostructures toward their excellent performance in flexible photodetectors.

One-dimensional (1D) Zn-based heterostructures have attracted considerable interest in the field of photodetection because of their tunable properties, flexibility, and unique optoelectronic properties. However, designing 1D multi-component Zn-based heterostructures for advanced photodetectors is still a great challenge. Herein, comb-like 1D-1D ZnO-ZnSe heterostructures with ZnO and ZnSe nanowires (NWs) comprising the shaft and teeth of a comb are reported. The length of the ZnO NWs can be modulated in the range of 300-1200 nm. Microstructural characterizations confirm that the 1D heterostructure clearly shows the spatial distribution of individual components. The well-designed structure displays an extended broadband photoresponse and higher photosensitivity than pure ZnSe NWs. Furthermore, ZnSe NWs with an appropriate length of ZnO branches show increased photoresponses of 3835% and 798% compared to those of pure ZnSe NWs under green and red-light irradiation, respectively. In addition, the integrated flexible photodetector presents excellent folding endurance after 1000 bending tests. This well-designed structure has significant potential for other 1D-based semiconductors in optoelectronic applications.

Structural stability, electronic, magnetic, thermoelectric, optical and thermodynamic properties of CoTiFeGe and Co2Fe0.25Mn0.75-xTixGe alloys

Density Functional Theory (DFT) calculations are performed using full potential linearized augmented plane wave (FP-LAPW) method to study CoTiFeGe and Co2Fe0.25Mn0.75-xTixGe (x = 0, 0.25, 0.50, 0.75) systems through GGA and mBJ-GGA formalisms. The lattice equilibrium optimization was conducted to determine the stable magnetic phase state of these systems. It was found that the systems exhibit stability in a ferromagnetic nature, with the exception of the Co2Fe0.25Mn0.75Ge compound, which displays ferrimagnetic behavior. Electronic band structures and density of states for our systems show a half-metallic character using mBJ-GGA, except the Co2Fe0.25Mn0.75Ge system, which exhibits metallic behavior. Furthermore, the studied systems adhere to the Slater-Pauling rule condition for half-metallicity of alloys Mtot = ZV-24. Optoelectronic properties have been analyzed using optical parameters, confirming semiconducting behavior. Optical reflections with minimal loss and the existence absorption are observed in the infrared and visible areas suggest that the studied systems are suitable for optoelectronic devices. Additionally, a comprehensive assessment of the thermodynamic properties of the systems was carried out to investigate their thermodynamical stability against temperature and pressure change. The transport properties of these systems were systematically investigated, revealing that our alloys present the poor thermoelectric matter.

Rapid and large-scale synthesis of MoS2 via ultraviolet laser-assisted technology for photodetector applications

Two-dimensional transition metal dichalcogenide (TMDC) thin films have been extensively employed in microelectronics research. Molybdenum disulfide (MoS2), as one of prominent candidates of this class, has been applied in photodetectors, integrated electronic devices, gas sensing, and electrochemical catalysis, owing to its extraordinary optoelectronic, chemical, and mechanical properties. Synthesis of MoS2 crystal film is the key to its application. However, the reported technology revealed several drawbacks, containing limited surface area, prolonged high-temperature environment, and unsatisfying crystallinity. In order to enhance the convenience of MoS2 applications, there is a pressing need for optimized fabrication technology, which could be quicker, with a large area, with adequate crystallinity and heat-saving. In this work, we presented an ultraviolet laser-assisted synthesis technology, accomplishing rapid growth (with the growth rate of about 40 μm s−1) of centimeter-scale MoS2 films at room temperature. To achieve this, we self-assembled a displaceable reaction chamber system, coupled with krypton fluoride ultraviolet pulse laser. The laser motion speed and trajectory could be customized in the software, allowing the maskless patterning of crystal films. As application, we exhibited a photodetector with the integration of synthesized MoS2 and lead sulfide colloidal quantum dots (PbS CQDs), displaying broadband photodetection from ultraviolet, visible to near-infrared spectrum (365–1550 nm), with the detectivity of 109–1010 Jones, and the rising time of 0.2–0.3 s. This work not only demonstrated a high-process-efficiency synthesis of TMDC materials, but also has opened up new opportunities for ultraviolet laser used in optoelectronics.

Hafnium dinitride/poly(9-vinylcarbazole) heterojunction: Structural, electronic, optical and vibrational properties. A DFT and DFPT study

Photosensitivity of semiconducting polymers can be enhanced by blending donor and acceptor polymers to optimize photoinduced charge separation. With a motivation to understand microscopic aspects of HfN2 and PVK relevant to optoelectronic properties of transition metal-dinitride/semiconductor interfaces, we examined their structural, electronic, optical and vibrational properties using first-principles calculations based on density functional theory (DFT) and density functional perturbation theory (DFPT) levels of theory. We computed a large direct energy gap of 3.751 eV for PVK and an indirect narrow band gap of 1.396 eV in HfN2. The gap value computed for the composite structure, HfN2/PVK, was 0.958 eV. The heterojunction displayed an indirect energy gap. The charge transfer between HfN2 and PVK results in a polarized field within the interface region, which will benefit the separation of photogenerated carriers. The calculated density of electronic states, Lowdin charge transfer and charge density difference certify that this proposed layered nanoheterojunction is an excellent light-harvesting semiconductor. These findings indicate that the conjugated polymer PVK is a promising candidate as a non-noble metal co-catalyst for HfN2 photocatalysis. It also provides useful information for understanding the observed enhanced photocatalytic mechanisms in experiments.

Topological polarons in halide perovskites.

Halide perovskites emerged as a revolutionary family of high-quality semiconductors for solar energy harvesting and energy-efficient lighting. There is mounting evidence that the exceptional optoelectronic properties of these materials could stem from unconventional electron-phonon couplings, and it has been suggested that the formation of polarons and self-trapped excitons could be key to understanding such properties. By performing first-principles simulations across the length scales, here we show that halide perovskites harbor a uniquely rich variety of polaronic species, including small polarons, large polarons, and charge density waves, and we explain a variety of experimental observations. We find that these emergent quasiparticles support topologically nontrivial phonon fields with quantized topological charge, making them nonmagnetic analog of the helical Bloch points found in magnetic skyrmion lattices.

Anti-perovskites for Photovoltaics: Materials Development and Challenges

Abstract For the next-generation solar cells with excellent device efficiency and stability, designing advanced light absorber materials with exceptional optoelectronic properties is extremely crucial. Perovskites have attracted great attention due to their high-power conversion efficiency, and low fabrication cost. Eventhough perovskites achieved the highest efficiency of 25.7% within a decade, lead (Pb) toxicity is one of the main issues that needs to be addressed. Also, they are susceptible to degradation under ambient conditions. On the other hand, anti-perovskites, which are electronically inverted perovskites, possess structural flexibility, environmentally benign chemical composition, appropriate band gap and hence, have the capability to replace perovskites as the absorber layer for next-generation solar cells. Thus, a thorough assessment is urgently required to spark widespread concern in this family of compounds. Based on the current research progress, the potential of anti-perovskites in solar cell research is compiled in this study. The structural variety, optoelectronic characteristics, and uncharted territory of these compounds are covered in great detail. Finally, we have discussed the future research directions for the development of anti-perovskite materials for the next generation efficient and stable solar cells.

Synthesis, characterisation and voltammetric study of dimethylammonium lead iodide perovskite

In the last decade, the most investigated perovskite materials are the hybrid organic-inorganic perovskites (HOIPs) due to their optoelectronic properties and possible application in the production of photovoltaics. This interest has led to an ongoing search for new HOIP variants, alongside thorough investigations of the properties of existing HOIPs. That is why our research in the field of organic-inorganic perovskites is aimed at the synthesis, characterization, and investigation of the electrochemical properties of dimethylammonium lead iodide (DMAPbI3) using voltammetric studies. A modified synthesis of DMAPbI3, differing slightly from the one described in the literature, was performed by combining stoichiometric amounts of lead iodide (PbI2) and dimethylammonium iodide (DMAI) dissolved in acetonitrile. After conducting controlled evaporation, a yellow crystalline powder of DMAPbI3 was obtained. The identity and purity of the obtained compound were confirmed by powder X-ray diffraction (PXRD), infrared (IR) and Raman spectroscopy, and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX). Investigations on the electrochemical properties of DMAPbI3 by cyclic voltammetry were performed with dichloromethane (DCM) and tetrabutylammonium chloride (TBAC) as the electrolyte. A paraffin-impregnated graphite electrode (PIGE) was used as a working electrode, on which the perovskite microparticles were immobilized. The electrochemical activity of DMAPbI3 is recognized through an intense, broad, and irreversible anodic peak attributed to the oxidation of the constituents to different possible products and the decomposition of the perovskite structure.

Controlled Fracture‐Based Micropatterning of Ruddlesden–Popper Halide Perovskite for Ultra High‐Density Arrays of Micro Light Emitting Diodes

AbstractQuasi‐2D Ruddlesden–Popper perovskite (RPP) have surfaced as a promising candidate for light emitting diodes (LEDs) due to its outstanding optoelectronic properties. However, a reliable approach for patterning RPPs remains elusive due to the use of polar solvents in lithographic processes, which can damage the RPP. Here, a reliable and damage‐free dry micropatterning method of RPPs is reported, which also offers a cost/time advantage compared to conventional patterning methods. The sharp edges of high aspect ratio silicon micropillars are used to cut RPPs to a pre‐defined shape and then the cut RPPs are delaminated to obtain a patterned array of RPPs. The resultant patterned array exhibits no sign of degradation or discernable difference between adjacent pixels, achieving a ≈100% yield. The obtained array is utilized to fabricate a pixelated LED where a sharp electroluminescence (EL) spectrum peaking at 410 nm with full‐width‐at‐half‐maximum (FWHM) of 10 nm is observed. The pixelated devices demonstrate the potential to suppress EQE drops as the pixel size decreases, attributed to both the damage‐free micropatterning process and the defect tolerance of RPPs. Moreover, further improvements of the patterning method are demonstrated to avoid parasitic emission and suggest a promising strategy to fabricate pixel‐accessible micro‐LEDs.

Theoretically designed M@diaza[2.2.2]cryptand complexes: the role of non-covalent interactions in promoting NLO properties of organic electrides

ABSTRACT Organic excess electron compounds with significant nonlinear optical (NLO) properties are widely employed in optoelectronic applications. Herein, single-alkali metals with diaza[2.2.2] cryptand (M@crypt,M=Li, Na, and K) are investigated for optoelectronic and NLO properties by using the density functional theory. Thermodynamic and kinetic stabilities of present complexes are computed through interaction energy (Eint) and ab-initio molecular dynamic (AIMD) simulations. M@crypt complexes carry excess electrons and mimic molecular electrides. Quantum theory of atoms in molecules (QTAIM) analysis and reduced density gradient (RDG) spectra demonstrate the roles of the weak van der Waals (vdW) interactions between metal and complexant. The remarkable hyperpolarizability (βo) value up to 1.41 × 106 au may be credited to the presence of loosely bound excess electrons. The hyper Rayleigh scattering hyperpolarizability (βHRS) is recorded up to 1.31 × 106 au for the K@crypt. Furthermore, frequency-dependent first-order and second-order hyperpolarizability is more prominent at the applied frequency of ω = 0.042823 au. The electron localizing function (ELF) and localized orbital locator (LOL) analysis further disclose the nature of interaction between alkali metal and complexant. The TD-DFT method is adopted to get excited state parameters and absorbance properties. An electron density difference map (EDDM) is exploited to evaluate the orbital contributions in excited states. Hence, the studied electride may become a promising candidate for NLO materials. We anticipate that the present work will provide insight into further development of molecular electride for optoelectronic applications.

Ferroelasticity in Two-Dimensional Hybrid Ruddlesden-Popper Perovskites Mediated by Cross-Plane Intermolecular Coupling and Metastable Funnel-like Phases.

Ferroelasticity is a phenomenon in which a material exhibits two or more equally stable orientation variants and can be switched from one form to another under an applied stress. Recent works have demonstrated that two-dimensional layered organic-inorganic hybrid Ruddlesden-Popper perovskites can serve as ideal platforms for realizing ferroelasticity, however, the ferroelastic (FE) behavior of structures with a single octahedra layer such as (BA)2PbI4 [BA = CH3(CH2)3NH3+] has remained elusive. Herein, by using a combined first-principles and metadynamics approach, the FE behavior of (BA)2PbI4 under mechanical and thermal stresses is uncovered. FE switching is mediated by cross-plane intermolecular coupling, which could occur through multiple rotational modes, rendering the formation of FE domains and several metastable paraelastic (PE) phases. Such metastable phases are akin to wrinkled structures in other layered materials and can act as a "funnel" of hole carriers. Thermal excitation tends to flatten the kinetic barriers of the transition pathways between orientation variants, suggesting an enhanced concentration of metastable PE states at high temperatures, while halogen mixing with Br raises these barriers and conversely lowers the concentration of PE states. These findings reveal the rich structural diversity of (BA)2PbI4 domains, which can play a vital role in enhancing the optoelectronic properties of the perovskite and raise exciting prospects for mechanical switching, shape memory, and information processing.

General Synthesis of Metal Indium Sulfide Atomic Layers for Photocatalysis.

The metal indium sulfides have attracted extensive research interest in photocatalysis due to regulable atomic configuration and excellent optoelectronic properties. However, the synthesis of metal indium sulfide atomic layers is still challenging since intrinsic non-van-der-Waals layered structures of some components. Here, a surfactant self-assembly growth mechanism is proposed to controllably synthesize metal indium sulfide atomic layers. Eleven types of atomic layers with tunable compositions, thickness, and defect concentrations are successfully achieved namely In2S3, MgIn2S4, CaIn2S4, MnIn2S4, FeIn2S4, ZnIn2S4, Zn2In2S5, Zn4In16S33, CuInS2, CuIn5S8, and CdIn2S4. The typical CaIn2S4 shows a defect-dependence activity for CO2 photoreduction. The designed S vacancies in CaIn2S4 can serve as catalytic centers to activate CO2 molecules via localized electrons for π-back-donation. The engineered S vacancies tune the non-covalent interaction with CO2 and intermediates, manages to tune the free energy, and lower the reaction energy barrier. As a result, the defect-rich CaIn2S4 displays 2.82× improved reduction rate than defect-poor CaIn2S4. Meantime, other components also display promising photocatalytic performance, such as Zn2In2S5 with a H2O2 photosynthesis rate of 292µmolg-1h-1 and CuInS2 with N2-NH4 + conversion rate of 54µmolg-1h-1. This work paves the way for the multidisciplinary exploration of metal indium sulfide atomic layers with unique photocatalysis properties.

Nanoscale Cu2ZnSnSxSe(4−x) (CZTS/Se) for Sustainable Solutions in Renewable Energy, Sensing, and Nanomedicine

The importance and breadth of applications of the family of quaternary chalcogenides with the formula Cu2ZnSnSxSe(4−x) (CZTS/Se) where x = 0–4 are steadily expanding due to the tunable optoelectronic properties of these compounds and the Earth abundance of the elements in their composition. These p-type semiconductors are viewed as a viable alternative to Si, gallium arsenide, CdTe, and CIGS solar cells due to their cost effectiveness, Earth’s crust abundance, and non-toxic elements. Additionally, CZTS/Se compounds have demonstrated notable capabilities beyond solar cells, such as photoelectrochemical CO2 reduction, solar water splitting, solar seawater desalination, hydrogen production, and use as an antibacterial agent. Various routes have been explored for synthesizing pure CZTS/Se nanomaterials and significant efforts have been dedicated to reducing the occurrence of secondary phases. This review focuses on synthetic approaches for CZTS/Se nanomaterials, with emphasis on controlling the size and morphology of the nanoparticles and their recent application in solar energy harvesting and beyond, highlighting challenges in achieving the desired purity required in all these applications.

Tunable optoelectronic, thermoelectric, and photocatalytic properties of β-SiTe and SiH monolayers as a photocatalytic water-splitting

Tunable optoelectronic, thermoelectric, and photocatalytic properties of β-SiTe and SiH monolayers as a photocatalytic water-splitting

First-principles study of Na2AgAsZ6 (Z = F, Cl, Br, I) of structural, elastic, optoelectronic, and transport properties of lead-free halide double perovskites for energy conversion applications

In this article, density functional theory (DFT) is used to investigate the physical aspects of the halide double perovskites Na2AgAsZ6 (Z = F, Cl, Br, I). These substances have a cubic arrangement and are classified under space group Fm3m (225) based on their octahedral and tolerance factors values. All the perovskites are determined to be thermodynamically stable, as indicated by their negative formation energy. These double perovskite materials are semiconductors based on their electronic band structure. The energy band gaps of Na2AgAsF6, Na2AgAsCl6, Na2AgAsBr6, and Na2AgAsI6 were determined to be 2.96 eV, 1.93 eV, 1.28 eV, and 0.68 eV, respectively. We also calculated and examined the optical properties of these substances in the photon energy range of 0–8 eV. Our results indicate that the majority of the absorption occurs in the visible-ultraviolet spectrum, which makes the materials well-suited for solar systems. We employed the BoltzTraP algorithm to compute the thermoelectric properties of the materials and establish their thermoelectric behavior. These materials demonstrated figures of merit values of 0.55, 0.71, 0.74, and 0.75, respectively. Thus, these materials are appropriate for application in photovoltaic and thermoelectric devices.