Important Optoelectronic Properties Research Articles

Preparation and characterization of Cu-In-Ga-Se thin films by the electrodeposition technique using different metal salts and substrates

Cu(In, Ga)Se2 thin films possess important optoelectronic properties desirable for their application in devices such as solar cells. Solar cells based on this material have reached higher efficiencies than 23%. However, the commercialization of these cells has been restricted due to the use of thin film deposition methods involving costly high vacuum and cost. To reduce costs, it is necessary to use methods that do not use a high vacuum, among which electrodeposition stands out. Unfortunately, solar cells produced with this technique have yet to achieve high conversion efficiencies. Several authors attribute the lower efficiencies in such cells to the use of chemical additives in the preparation, different substrates, different deposition temperatures, etc. Nevertheless, there are very few reports on the influence of other metal salts in electrolytic baths. This work aims to use three different types of metal salts and voltages to produce Cu(In, Ga)Se2 (CIGS) absorber thin films by co-electrodeposition technique. The effect of nucleation type with two different substrates is studied, also report the studies carried out on the atomic composition and structural, morphological, and electrochemical characterization to understand the formation, growth, and morphology of CIGS films and, in this way, to obtain a suitable stoichiometry of thin film solar cells using this absorber.

Experimental structural and optoelectronic properties and theoretical investigation of novel square planar nickel (II) complex with (o-tolyldiazenyl) naphthalen-2-ol ligand

This study involves the preparation of a new nickel (II) complex dye [Ni-L2] and its ligand [HL]. Both materials have been characterized by elemental analyses, IR, NMR, UV-vis, X-ray crystallography, optoelectronic properties and Hirshfeld surface analysis. The spectroscopic studies on HL have revealed that it exists in two tautomeric forms (Azo - Hydrazone), in which the second tautomer was more stable. The X-ray study has indicated that a monoclinic system is present in the Ni-L2. In addition, the coordination sphere around the metal centre consisted of two oxygen atoms and two nitrogen atoms from chelating ligands to give a square planar geometry. The role of various interatomic interactions has also been evaluated and analyzed with Hirshfeld surface analysis. Finally, important optoelectronic properties such as experimental spectroscopic, optical band gaps, refractive indices, dispersion and media behavior of the nickel complex dissolved in different solvents have been extensively investigated.

Organic semiconductor nanostructures: optoelectronic properties, modification strategies, and photocatalytic applications

Organic semiconductors (OSCs) possess diverse chemical structures and tailored optoelectronic properties via simple chemical modifications, so increasing use of them are found in efficient visible-light photocatalysis. However, the weak chemical bonds and the poor charge behavior (e.g., low concentration of free charge carriers, low carrier mobility) intrinsic in them, always incur quite limited stability and efficiency. Therefore, the assembly of them into refined nanostructures or nanocomposites is usually proposed to enhance their optoelectronic properties, as well as the photocatalytic efficiency and reliability. Zero-dimensional (0D) nanoparticles are low in size and hence high specific surface area (SSA); One-dimensional (1D) nanostructures are usually arranged in an orderly long range thus leading to low surface defect density and increased carrier mobility; Two-dimensional (2D) nanostructures are particularly capable of enhancing the photogenerated charge utilization because of their large reaction sites and shortened charge transport length. Furthermore, the building of heterogeneous interfaces in the nanocomposites can effectively facilitate the special charge separation. All these highlight the importance of organic nanostructures in improving the photocatalytic activity and stability. Therefore, organic semiconductor nanostructures (OSNs) have been increasingly used in the photocatalytic water splitting into H2 and O2, CO2 reduction, pollutant decomposition, disinfection, etc. In this review, we first examine the important optoelectronic properties of OSNs that govern the photocatalytic processes; we then analyze different classes of OSNs and their mechanistic pathways, with an emphasis on the structure-property relationships; we also introduced various photocatalytic applications of OSNs; we lastly propose the challenges and future outlook in real use.

Two-Step Patterning of Scalable All-Inorganic Halide Perovskite Arrays.

Halide perovskites have many important optoelectronic properties, including high emission efficiency, high absorption coefficients, color purity, and tunable emission wavelength, which makes these materials promising for optoelectronic applications. However, the inability to precisely control large-scale patterned growth of halide perovskites limits their potential toward various device applications. Here, we report a patterning method for the growth of a cesium lead halide perovskite single crystal array. Our approach consists of two steps: (1) cesium halide salt arrays patterning and (2) chemical vapor transport process to convert salt arrays into single crystal perovskite arrays. Characterizations including energy-dispersive X-ray spectroscopy and photoluminescence have been employed to confirm the chemical compositions and the optical properties of the as-synthesized perovskite arrays. This patterning method enables the patterning of single crystal cesium lead halide perovskite arrays with tunable spacing (from 2 to 20 μm) and crystal size (from 200 nm to 1.2 μm) in high production yield (almost every pixel in the array is successfully grown with converted perovskite crystals). Our large-scale patterning method renders a platform for the study of fundamental properties and opportunities for perovskite-based optoelectronic applications.

Optoelectronic properties of multiple quantum barriers nano-scale avalanche photo diodes

The important optoelectronic properties like spectral response, excess noise characteristics, time and frequency response of multiple quantum barrier (MQB) nano-scale avalanche photodiodes (APDs) based on Si~3C-SiC material system have been studied. A self-consistent simulation method based on quantum drift-diffusion model has been presented. Simulation results show that the Si~3C-SiC MQB nano-APDs are capable of detecting significantly longer wavelengths as compared to infrared flat Si APDs. The multiplication gain and excess noise factor (ENF) of the MQB APDs have been calculated by varying the number of quantum barriers (QBs). The numerically calculated ENF values of MQB APDs have been compared with the ENF of Si flat conventional APDs of similar dimensions and it is observed that the use of QBs leads to significant reduction in ENF of the APDs. Simulation results also show that MQB nano-APDs possess significantly faster time response and wider frequency response as compared to the Si counterparts.

Insights into the Metal-catalyzed Alkyne Hydroarylation Reactions and Related Processes for the Synthesis of Coumarins

Coumarin derivatives play an important role in many different biomedical and technological applications. As “privileged” scaffolds, coumarin derivatives display interesting biological and important optoelectronic properties. The practical significance of coumarin molecules has encouraged extensive efforts toward their synthesis. Although classical methods, such as the Perkin, Pechmann and Knoevenagel reactions for the synthesis of a wide variety of substituted coumarins, are still actively used, these methods suffer several limitations. Nowadays, alternative new efficient syntheses of coumarin derivatives are constantly evolving and being of considerable interest. The hydroarylation reaction of alkynes, using transition metals catalysts, is considered one of the most prospective tools for rapid accessing to coumarin scaffolds in an efficient and atom-economical manner. This coumarin construction could be achieved through inter- or intramolecular reactions of respective phenols and alkynes or aryl alkynoates. The present review mainly covers recent studies on new methods for the synthesis of coumarin derivatives via alkenylation of phenols with alkynes, aryl alkynoates and related reagents or direct functionalization of alkynoates. The information provided should furnish a fresh insight for organic chemists in the design of novel molecules that contain the coumarin skeletons. Keywords: Functionalized coumarins, hydroarylation reactions, C-C bond formation, alkynoates, transition-metal-catalyzed process, direct intramolecular alkyne functionalization.

Surface Termination, Morphology, and Bright Photoluminescence of Cesium Lead Halide Perovskite Nanocrystals

Colloidal cesium lead halide perovskite nanocrystals (CsPbX3 PNCs, X = Cl, Br, I) exhibit important optoelectronic properties that make them amenable for a plethora of applications. However, the origin of these properties, even for as-synthesized and unpurified PNCs, is largely unknown. Electronic structure calculations are therefore essential to understand with atomistic detail the properties of these nanomaterials; however, finding a model for PNCs that resembles the experiments is a challenging task. Essentially, the main problem is how to correctly terminate a PNC surface that is comprised of a large fraction of the nanocrystal atoms and of ligands employed in the synthesis. Here, we construct nominally trap-free models for PNCs taking into account experimental conditions. With density functional theory we analyze the effect of size, shape, and halide composition on the electronic structure of PNCs. We confirm that the PNC crystalline core exhibits an orthorhombic structure, and we demonstrate that PN...

Optoelectronic properties of naphtho[2, 1-b:6, 5-b′]difuran derivatives for photovoltaic application: a computational study

Some important optoelectronic properties of naphtho[2,1-b:6,5-b']difuran (DPNDF) and its two derivatives have been limelighted by applying the density functional theory (DFT). Due to their low cost, high stability and earth abundance, the DPNDF and its derivatives are considered as potential organic semiconductor materials for their optoelectronics applications. Highly proficient derivatives are obtained systematically by attaching -CN (cyanide) to DPNDF at various sites. Our calculations indicate that DPNDF has a wide and direct band gap with an energy gap of 3.157eV. Whereas the band gaps of its derivatives are found to be decreased by 88meV for derivative "a" and 300meV for derivative "b" as a consequence of p orbitals present in C and N atoms in derivative structures. The narrowing of the energy gap and density of states for the derivatives of DPNDF in the present investigation suggest that energy gap can be engineered for desirable optoelectronic applications via derivatives designing. Furthermore, their obtained results for optical parameters such as the dielectric and conductivity functions, reflectivity, refractive index, and the extinction coefficients endorses their aptness for optoelectronic applications. Graphical Abstract Real part of dielectric function for derivative "b".

RAMAN Characterization of Ge1-XSnX Allows By Using a SPACE Correlation MODEL

Ge1-xSnx alloys present important optoelectronic properties due to the possibility for obtain a direct and tunable energy gap group IV semiconductor. Ge1-xSnx alloys were grown on different substrates by using a R. F. Magnetron Sputtering. Raman spectroscopy and HRXRD were used in order to determinate the structural properties of these alloys. We determined a linear shift of the Raman peak that depends directly on the Sn concentration of the alloy. We also find that the Raman peak has an asymmetrical shape attributed to a small crystal size. In this work we present the characterization of the Raman peaks by fitting a Space Correlation Model. We obtain a strong correlation among FWHM, asymmetrical shape and Sn concentration of the alloys. Keywords: HRXRD, Raman.

Imaging Excited Orbitals of Quantum Dots: Experiment and Electronic Structure Theory.

Electronically excited orbitals play a fundamental role in chemical reactivity and spectroscopy. In nanostructures, orbital shape is diagnostic of defects that control blinking, surface carrier dynamics, and other important optoelectronic properties. We capture nanometer resolution images of electronically excited PbS quantum dots (QDs) by single molecule absorption scanning tunneling microscopy (SMA-STM). Dots with a bandgap of ∼1 eV are deposited on a transparent gold surface and optically excited with red or green light to produce hot carriers. The STM tip-enhanced laser light produces a large excited-state population, and the Stark effect allows transitions to be tuned into resonance by changing the sample voltage. Scanning the QDs under laser excitation, we were able to image electronic excitation to different angular momentum states depending on sample bias. The shapes differ from idealized S- or P-like orbitals due to imperfections of the QDs. Excitation of adjacent QD pairs reveals orbital alignment, evidence for electronic coupling between dots. Electronic structure modeling of a small PbS QD, when scaled for size, reveals Stark tuning and variation in the transition moment of different parity states, supporting the simple one-electron experimental interpretation in the hot carrier limit. The calculations highlight the sensitivity of orbital density to applied field, laser wavelength, and structural fluctuations of the QD.

ChemInform Abstract: Water Soluble Polythiophenes: Preparation and Applications

AbstractReview: 129 refs.

Effect of Co Doping on Crystallographic and Optoelectronic Properties of ZnO Thin Films

In this study, Co-doped ZnO thin film was deposited by spray pyrolysis technique at 230 ∘C followed by annealing at 350 ∘C for 1 h. Crystal structure was investigated by X-ray diffraction method. All the samples showed polycrystalline hexagonal wurtzite structure. Variation of lattice parameters, volume of unit cell, and Zn–O bond length were investigated. The surface morphology of the films was studied by SEM measurements and wrinkled surface were observed for the Co-doped ZnO films. The optical characterization of the annealed samples was performed. The observed band gap values were found to decrease on Co doping in ZnO thin films. The effect of Co substitution on important optoelectronic properties, such as variation of the extinction and absorption coefficient, refractive index, and dielectric constant of the ZnO thin films were thoroughly investigated. It was found that Co doping has significant effect on these properties over a certain range of wavelength.

Comparison of the electronic structure of different perylene‐based dye‐aggregates

Aggregates of functionalized polycyclic aromatic molecules like perylene derivatives differ in important optoelectronic properties such as absorption and emission spectra or exciton diffusion lengths. Although those differences are well known, it is not fully understood if they are caused by variations in the geometrical orientation of the molecules within the aggregates, variations in the electronic structures of the dye aggregates or interplay of both. As this knowledge is of interest for the development of materials with optimized functionalities, we investigate this question by comparing the electronic structures of dimer systems of representative perylene-based chromophores. The study comprises dimers of perylene, 3,4,9,10-perylene tetracarboxylic acid bisimide (PBI), 3,4,9,10-perylene tetracarboxylic acid dianhydride (PTCDA), and diindeno perylene (DIP). Potential energy curves (PECs) and characters of those electronic states are investigated which determine the optoelectronic properties. The computations use the spin-component-scaled approximate coupled-cluster second-order method (SCS-CC2), which describes electronic states of predominately neutral excited (NE) and charge transfer (CT) character equally well. Our results show that the characters of the excited states change significantly with the intermolecular orientation and often represent significant mixtures of NE and CT characters. However, PECs and electronic structures of the investigated perylene derivatives are almost independent of the substitution patterns of the perylene core indicating that the observed differences in the optoelectronic properties mainly result from the geometrical structure of the dye aggregate. It also hints at the fact that optical properties can be computed from less-substituted model compounds if a proper aggregate geometry is chosen.

Structural and optoelectronic properties of amorphous and microcrystalline silicon deposited at low substrate temperatures by RF and HW CVD

AbstractThe structural and optoelectronic properties of silicon thin films prepared by hot wire chemical vapor deposition and radio frequency plasma enhanced chemical vapor deposition are studied in the range of substrate temperatures (Tsub)from 100 °C to 25 °C. The defect density, structure factor and bond angle disorder of amorphous silicon films (a-Si:H) deposited by both techniques are strongly improved by the use of hydrogen dilution. Correlation of these structural properties with important optoelectronic properties, such as photo-to-dark conductivity ratio, is made. Microcrystalline silicon (μc-Si:H) is obtained using HW with a large crystalline fraction for hydrogen dilutions above 85% independently of Tsub. The deposition of μc-Si:H by RF requires increasing the hydrogen dilution and shows decreasing crystalline fraction as Tsub is decreased. The properties of the low Tsub films are compared to those of samples produced at 175 °C and 250 °C in the same reactors.

Thermal wave photopyroelectric characterization of advanced materials: State of the art

Abstract This article reviews the history, background, theoretical basis, development, attempts to optimize, and experimental performance of the photopyroelectric technique for the optothermal characterization of advanced materials such as semiconductors, superconductors, pure metals and alloys, quantum wells, liquid crystals, paramagnetic and ferromagnetic materials, as well as solar cells. The state of the art in the experimental processes in this field is also reviewed. This new photothermal technique can be used after a careful optimization, as a highly sensitive method for photopyroelectric spectroscopy and general thermal wave measurements. It has been shown to be a highly sensitive spectroscopic method for the nondestructive evaluation of advanced materials. This review presents the main photopyroelectric theoretical models that have been used for the extraction of some important optoelectronic properties such as the optical absorption coefficient and the nonradiative quantum efficiency spectra, as well as some thermal properties such as the thermal diffusivity, thermal conductivity, and specific heat. The applicability of the general basic theoretical model with its many special cases is also described in detail. This review demonstrates how photopyroelectric spectroscopy can be complementary to the conventional spectroscopic methods. The different experimental modes of the technique are also discussed. Moreover, some ideas concerning future perspectives of applying the technique to other scientific fields are outlined. This article does not aspire to an in-depth analysis of the experimental results in the field; rather, it focuses on the technique itself.