Band Gap Absorption Research Articles

Atomistic insight into the device engineering of inorganic halide perovskite solar cells

Perovskites provide a promising pathway for fabricating efficient and lightweight solar cells, which could be game-changers in the renewable energy landscape. Yet, the phase stability and device design are still the key issues of perovskite-based photovoltaics. Herein, we evaluated the phase stability of CsPbX3 (X = I, Br, and Cl) upon analyzing the lattice dynamics from first-principles and then predicted fundamental properties including bandgap, carrier mobility, and optical absorption as input to optimize the device design of solar cell. A maximum power conversion efficiency (PCE) of 12.36 % was achieved for a CsPbBr3-based solar cell. Those findings highlight the potential of CsPbX3 perovskites for high-efficiency solar cells. The computational approach provides a comprehensive understanding of the material's structural stability, charge-carrier dynamics, and optoelectronic characteristics. The collective analysis enables a holistic understanding of CsPbX3 perovskites and provides a roadmap for future advancements in perovskite solar-cell technology.

CdWO4 Sub-1 nm Nanowires for Visible-Light CO2 Photoreduction.

Quantum size effect usually causes energy level splitting and band broadening as material size decreases. However, this may change again by the surface adsorbents, doping and defects, which rarely attracts much attention. Herein, CdWO4 sub-1 nm nanowires (SNWs) with oleylamine adsorption, PO4 3--doping and oxygen defects are synthesized by combining Cd(CH3COO)2, H3PW12O40 (PW12) and oleylamine (abbreviated as PO4 3--CdWO4-X SNWs). Compared with bulk CdWO4, they exhibit unexpected absorption spectra (extended from 292 nm to 453 nm) and band gap (reduced from 4.25 eV to 2.74 eV), thus bringing remarkable visible-light CO2 photoreduction activity. Under 410 nm LED light irradiation, PO4 3--CdWO4-40 SNWs exhibit the highest photocatalytic performance with a CO2-to-CO generation rate of 1685 μmol g-1 h-1. Density functional theory (DFT) calculations demonstrate the adsorbed oleylamine raises the valence band and enhances the adsorption of reaction substrate and intermediates, thus decreasing their reduction energy barriers. Furthermore, PO4 3--doping and oxygen defects will generate defect energy band below the conduction band of PO4 3--CdWO4-40 SNWs, resulting in remarkable visible light absorption and superior photocatalytic CO2 reduction performance. This work highlights the significant impacts of surface adsorbents, doping and defects on the physicochemical and catalytic properties of sub-nano materials.

CdWO4 Sub‐1 nm Nanowires for Visible‐light CO2 Photoreduction

Quantum size effect usually causes energy level splitting and band broadening as material size decreases. However, this may change again by the surface adsorbents, doping and defects, which rarely attracts much attention. Herein, CdWO4 sub‐1 nm nanowires (SNWs) with oleylamine adsorption, PO43‐‐doping and oxygen defects are synthesized by combining Cd(CH3COO)2, H3PW12O40 (PW12) and oleylamine (abbreviated as PO43‐‐CdWO4‐X SNWs). Compared with bulk CdWO4, they exhibit unexpected absorption spectra (extended from 292 nm to 453 nm) and bandgap (reduced from 4.25 eV to 2.74 eV), thus bringing remarkable visible‐light CO2 photoreduction activity. Under 410 nm LED light irradiation, PO43‐‐CdWO4‐40 SNWs exhibit the highest photocatalytic performance with a CO2‐to‐CO generation rate of 1685 µmol g‐1 h‐1. Density functional theory (DFT) calculations demonstrate the adsorbed oleylamine raises the valence band and enhances the adsorption of reaction substrate and intermediates, thus decreasing their reduction energy barriers. Furthermore, PO43‐‐doping and oxygen defects will generate defect energy band below the conduction band of PO43‐‐CdWO4‐40 SNWs, resulting in remarkable visible light absorption and superior photocatalytic CO2 reduction performance. This work highlights the significant impacts of surface adsorbents, doping and defects on the physicochemical and catalytic properties of sub‐nano materials.

Optimizing deposition parameters and characterizing TiO2 thin films for future memristor applications

Titanium dioxide (TiO2) thin films were deposited on glass substrates using Spray Pyrolysis technique, with variations in multiple deposition parameters. The molarity of the precursor was altered within a small range from 0.09 M–0.15 M. The deposition temperature was systematically adjusted from 200 °C to 400 °C while the ratio between precursor and chelating agent varied between 1:1,1:2 and 1:3. The thickness of TiO2 films were found to be in the range of 216 nm to 14.9 μm. Structural analysis conducted by XRD confirmed the formation of anatase TiO2 thin films. Optical studies using UV-Visible spectrophotometer determined the absorption and indirect bandgap ranging from 299 nm to 326 nm and 3.08 eV to 3.44 eV respectively. Electrical studies carried out evaluated the leakage currents and DC resistivity for all individual films with the input voltage applied from ± 0.5 V to ± 5V. Impedance studies were conducted by varying input voltages from 0.2V–3V for each film, so as to examine the resultant impedance, dielectric constant, dielectric loss, conductivity, admittance and modulus spectra. The obtained results were analysed to optimise the deposition parameters for designing future memristors with specific individual or combined characteristics, such as high ON/OFF, switching speed, endurance and retention.

Lead-free Cs2TiBr6 perovskite solar cells achieving high power conversion efficiency through device simulation

Recently, lead-based perovskite solar cells (PSCs) have gained significant attention in the photovoltaic industry due to their remarkable properties such as high bandgap and high absorption coefficient. However, challenges such as toxicity, instability, and short shelf life limit the use of inorganic-organic lead-based PSCs. To address these issues, researchers introduced eco-friendly, lead-free, and stable cesium titanium (Cs2TiBr6) single-halide absorber material. The aim of this work is to perform the numerical modelling and simulation of FTO/SnO2/Cs2TiBr6/CBTS/Au structure incorporating interfacial defect layers (IDL) using SCAPS-1D to examine and study its characteristics properties about various photovoltaic (PV) parameters such as light-absorbing layer thickness, charge transport layer thickness, doping, defect density, operating temperature, and quantum efficiency (QE). After evaluating these parameters, the proposed single-halide Cs2TiBr6-based structure shows superior performance as compared to previously reported experimental and simulation-based Cs2TiBr6 perovskite structures. The results show a maximum power conversion efficiency (PCE) of 24.24 %, with a fill factor (FF) of 88.9 %, an open-circuit voltage (VOC) of 1.31 V, and a short-circuit current density (JSC) of 20.76 mA/cm2. This work encourages researchers to develop low-toxic, and stable PSCs for the future solar cell industry.

Roles of defects in perovskite CsPbX3 (X=I, Br, Cl): a first- principles investigation

Inorganic lead halide perovskite CsPbX3 (X=I, Br, Cl) have a promising application in optoelectronic fields due to their excellent photovoltaic properties. The defects, which have a significant impact on the performance of materials, are often introduced during the synthesis process. However, there is still a lack of systematic theoretical investigation of the effects of these defects. In this study, the effects of vacancies and H-atom interstitial point defects on the structural, electronic and optical properties of CsPbX3 are systematically investigated by using first-principles approach based on density-functional theory. The calculated results show that the introduction of different defects have significantly effect on the band gap, effective mass, semiconductor properties, ion migration and optical absorption coefficient of the perovskite materials. It is also found that VCs and VPb defects introduce shallow transition levels that do not negatively impact the optoelectronic properties. However, VX and interstitial H defects generate deep transition levels within the bandgap, which acts as non-radiative recombination centers and reduce the optoelectronic performance of the perovskite material. This study contributes to the understanding of the nature of halide chalcogenides and optimally regulating the performance of optoelectronic devices.

Structural and optoelectronic study of MgLiX3 (X= Cl, Br, and I) halide perovskites: A DFT approach

This article presents in-depth information on the structural and optoelectronic properties of MgLiX3 (X = Cl, Br, and I) perovskites, and it suggests that MgLiX3 perovskites are promising materials for use in a variety of optoelectronic gadgets. The structural and optoelectronic properties of the compounds are determined utilizing first-principles calculations, with the density functional theory applied through the WIEN2k code. The structural stability was verified by computing the formation energy and binding energy. This study investigated the behavior of electronic conductivity and determined the bandgap values by employing TB-mBJ, which are 3.354 eV (MgLiCl3), 1.728 eV (MgLiBr3), and 0.067 eV (MgLiI3). Furthermore, optical properties such as absorption coefficient, reflectivity, conductivity, loss function, dielectric function, refractive index, and extinction coefficient were calculated and analyzed. In the visible range, MgLiBr3 and MgLiI3 exhibit their primary highest peaks of the absorption coefficient, which are 8.8 × 104 cm−1 for MgLiBr3 and 7.7 × 104 cm−1 for MgLiI3. On the other hand, MgLiCl3 demonstrates its initial highest peaks in the UV range, that is, 9 × 104 cm−1. The findings indicate that among the compounds studied, MgLiBr3 shows promise as a candidate for manufacturing solar cell devices based on the SQ limit, bandgap for typical perovskites (within 0.8–2.2 eV), and absorption in the visible range. MgLiCl3 is suitable for manufacturing several optoelectronic devices, such as laser diodes (LDs) and UV sensors due to having a high absorption coefficient in the ultraviolet region. With its low energy bandgap and high absorption coefficient in the IR to VR regions, MgLiI3 is well-suited for manufacturing photodetectors, LEDs, and other optoelectronic devices.

Assessing the electromagnetic shielding effectiveness of coconut coir composites with varying iron particle concentrations

This study investigates the electromagnetic shielding effectiveness of Coconut Coir-based Porous Carbon (CCPC) composites with varying iron (Fe) particle concentrations, specifically focusing on four different weight ratios of CCPC/Fe-80, CCPC/Fe-60, CCPC/Fe-40, and CCPC/Fe-20. The novelty of this work lies in the use of sustainable coconut coir as a base material, emphasizing its eco-friendly and cost-effective attributes for Electromagnetic interference (EMI) shielding applications. The significance of varying iron particle concentrations is highlighted to optimize electromagnetic shielding effectiveness. Comprehensive analyses were conducted on these composites. X-Ray Diffraction (XRD) analysis confirmed the presence of crystalline Fe particles and amorphous carbon, with crystalline sizes determined via Williamson-Hall (W-H) plot, Scherrer Equation, and Strain Size Plot (SSP) ranging from 17.33 nm to 18.01 nm for the former. Raman spectroscopy revealed distinctive D and G bands, with intensity ratios indicating a slight increase in structural disorder with higher Fe content. UV-Visualization spectroscopy demonstrated distinct absorption peaks, with higher Fe content resulting in more pronounced absorbance and lower band gap energies. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) analyses provided detailed insights into the material's microstructure and elemental composition, confirming the successful integration of Fe particles within the porous carbon matrix. Vector Network Analyzer (VNA) testing measured the reflection loss (RL), showing values in the range of −26.4 dB to −20.2 dB, for 2 mm thick samples, corresponding to electromagnetic wave attenuation of over 99%. These results underscore the potential of CCPC/Fe composites, particularly in applications requiring effective Electromagnetic (EM) wave attenuation. This research offers a sustainable and cost-effective solution, contributing significantly to the field of materials science by enhancing electromagnetic compatibility in various technological applications.

Enhancing Multi-Junction Solar Cell Performance: Advanced Predictive Modeling and Cutting-Edge CIGS Integration Techniques

Historically, multi-junction solar cells have evolved to capture a broader spectrum of sunlight, significantly enhancing efficiency beyond conventional solar technologies. In this study, we utilized Silvaco TCAD tools to optimize a five-junction solar cell composed of AlInP, AlGaInP, AlGaInAs, GaInP, GaAs, InGaAs, and Ge, drawing on advancements documented in the literature. Our research focused on optimizing these cells through sophisticated statistical modeling and material innovation, particularly examining the relationship between layer thickness and electrical yield under one sun illumination. Employing III-V tandem solar cells, renowned for their superior efficiency in converting sunlight to electricity, we applied advanced statistical models to a reference solar cell configured with predefined layer thicknesses. Our analysis revealed significant positive correlations between layer thickness and electrical performance, with correlation coefficients (R2 values) impressively ranging from 0.86 to 0.96 across different regions. This detailed statistical insight led to an improvement in overall cell efficiency to 44.2. A key innovation in our approach was replacing the traditional germanium (Ge) substrate with Copper Indium Gallium Selenide (CIGS), known for its adjustable bandgap and superior absorption of long-wavelength photons. This strategic modification not only broadened the absorption spectrum but also elevated the overall cell efficiency to 47%. Additionally, the optimization process involved simulations using predictive profilers and Silvaco Atlas tools, which systematically assessed various configurations for their spectral absorption and current–voltage characteristics, further enhancing the cell’s performance. These findings underscore the critical role of precise material engineering and sophisticated statistical analyses in advancing solar cell technology, setting new efficiency benchmarks, and driving further developments in the field.

Synthesis of Substituted 4-Styrylcoumarins via Wittig Reaction: An Approach to Photophysical and DFT Studies

A novel coumarin derivative of4-(4-aminostyryl)-7-methyl-2H-chromen-2-one (5)was synthesized by the reaction of 4-(bromomethyl)-7-methyl-2H-chromen-2-one and p-nitro benzaldehyde using toluene at 120Co via standard Wittig reaction condition. The molecules were characterized by spectral analysis and the photophysicalproperties for organic electronic applications were examined, such as thermal stability, strong and broad optical absorption and emission studies. Optical properties are explicated by UV-Vis absorption and fluorescence spectroscopy andoptical band gaps of the molecules 4 and 5 are found to be 3.35eV-3.65eV as estimated from their onset absorption edge. The 4-(4-aminostyryl)-2H-chrome-2-one a coumarin showed high thermal stability up to 239-367 °C. Density functional theory computations were performed to understandintermolecular charge transfer property.

Gold Nanoparticles Modulate Excimer and Exciplex Dynamics of PDDCP-Conjugated Polymers.

How plasmonic nanostructures modulate the behavior of exciplexes and excimers within materials remains unclear. Thus, advanced knowledge is essential to bridge this gap for the development of optoelectronic devices that leverage the interplay between plasmonic and conjugated polymer hybrid materials. Herein, this work aims to explore the role of gold nanoparticles (AuNPs) in modulating exciplex and excimer states within the conjugated polymer poly(2,5-di(3,7-dimethyloctyloxy) cyanoterephthalylidene) (PDDCP), known for its photoluminescent and semi-conductive properties, aiming to create innovative composite materials with tailored optical features. The spectral analysis was conducted to investigate the effects of AuNPs on the PDDCP, varying AuNP volume percentages to measure changes in the absorption profile, molar extinction coefficient (ε), absorption cross-section (σa), and optical bandgap (Eg). Fluorescence spectra of the mixture at different volume ratios were also examined to assess exciplex formation, while amplified spontaneous emission (ASE) profiles were analyzed to study the behavior and photochemical stability of the polymer-NP hybrid material. Increasing AuNP volume induced both blue and red shifts in the absorption profile of the PDDCP. Higher AuNPs concentrations correlated with decreased ε and σa, inversely impacting Eg. The emission spectra obtained at varied AuNP volume ratios indicated significantly enhanced exciplex and excimer formations. The ASE profiles remained consistent but showed reduced intensity with increasing AuNPs concentrations, indicating their influence on hybrid material behavior and stability. The findings suggest that AuNPs affect PDDCP's optical characteristics, altering the absorption profile, bandgap, and fluorescence spectra. Furthermore, the observed reduction in ASE intensity highlights their influence on the behavior and photochemical stability of the hybrid material. These results contribute to a better understanding of the versatile applications of plasmonic-conjugated hybrid polymers.

Evaluating Photovoltaic Conversion Performance under Artificial Indoor Lighting

Several photovoltaic technologies, based on different semiconductor absorbers with band-gap energy in the range Eg = 1.0–1.5 eV are currently sharing the market for outdoor applications. These photovoltaic cells are designed to achieve an optimal photovoltaic conversion under solar illumination (represented by the standard AM1.5 global spectrum), but their performance changes under different artificial indoor lights. Here, the detailed balance principle that was first applied for an ideal photovoltaic absorber under solar radiation is now used by considering the actual spectra of four typical indoor lamps: incandescent, halogen, metal halide and white LED. For each particular illumination source, the theoretical maximum for short-circuit current, open-circuit voltage and maximum power point have been calculated and represented as a function of the absorber band-gap energy. Furthermore, the optical absorption spectra of some semiconductors with optimal solar conversion efficiencies are used to estimate their comparative performance under the various artificial light sources. It has been found that wide band-gap absorbers (Eg~1.9 eV) are needed to achieve a light-to-electricity conversion efficiency of 60% under LED illumination or 31% with metal halide bulbs, while a lowest band-gap energy of about 0.8 eV is required to obtain a maximum efficiency of 24% with incandescent and halogen lamps.

Phosphorus doped hydrogenated silicon oxycarbide: Film formation, properties and its application on silicon heterojunction solar cell

An ultrathin phosphorus doped hydrogenated microcrystalline silicon oxycarbide (n-μc-SiCO:H) layer deposited by plasma enhanced chemical vapor deposition (PECVD) method can be used as a window layer for silicon heterojunction solar cells. The optical and electrical properties of n-μc-SiCO:H films were controlled by PECVD deposition conditions. The interplay effects of H2, CO2 and PH3 to SiH4 gas ratio on the chemical composition, material structure and properties of n-μc-SiCO:H film were systematically determined. O, H, C and P atoms were observed to incorporate into the silicon network of n-μc-SiCO:H layer, while most of the atoms bond directly to Si atoms. Incorporation of oxygen and carbon atoms into n-μc-SiCO:H film, confirmed by XPS as formation of Si-O and Si-C bonds, enlarged the optical absorption band gap (Eg) value. Both film crystallinity and phosphorus concentration in n-μc-SiCO:H layer were observed to be controlled by the H2, CO2 and PH3 to SiH4 gas ratio. The electric performance of HJT solar cell was depended on the optical and electrical properties of n-μc-SiCO:H layer. An average efficiency (across ∼ 120 cells) of 26.32 % was achieved in cells with optimized deposition parameters for the n-μc-SiCO:H layer. The reaction gas ratio was also the dominant factor in determining the number and size of nanoscale Si crystallites embedded in the n-μc-SiCO:H layer. The conductivity of n-μc-SiCO:H layer was determined by the activated phosphorus concentration but independent of the total phosphorus concentration. It was also found that large concentrations of small Si crystallites of size less than 3 nm improved film conductivity.

Cairo pentagon tessellated covalent organic frameworks with mcm topology for near-infrared phototherapy

Despite the prevalent of hexagonal, tetragonal, and triangular pore structures in two-dimensional covalent organic frameworks (2D COFs), the pentagonal pores remain conspicuously absent. We herein present the Cairo pentagonal tessellated COFs, achieved through precisely chosen geometry and metrics of the linkers, resulting in unprecedented mcm topology. In each pentagonal structure, porphyrin units create four uniform sides around 15.5 Å with 90° angles, while tetrabiphenyl unit establish a bottom edge about 11.6 Å with 120° angles, aligning precisely with the criteria of Cairo Pentagon. According to the narrow bandgap and strong near-infrared (NIR) absorbance, as-synthesized COFs exhibit the efficient singlet oxygen (1O2) generation and photothermal conversion, resulting in NIR photothermal combined photodynamic therapy to guide cancer cell apoptosis. Mechanistic studies reveal that the good 1O2 production capability upregulates intracellular lipid peroxidation, leading to glutathione depletion, low expression of glutathione peroxidase 4, and induction of ferroptosis. The implementation of pentagonal Cairo tessellations in this work provides a promising strategy for diversifying COFs with new topologies, along with multimodal NIR phototherapy.

First-Principles Calculations on Electronic, Optical, and Phonon Properties of γ-Bi2MoO6.

The wide band gap γ-Bi2MoO6 (BMO) has tremendous potential in emergent solar harvesting applications. Here we present a combined experimental-first-principles density functional theory (DFT) approach to probe physical properties relevant to the light sensitivity of BMO like dynamic and structural stability, Raman and infrared absorption modes, value and nature of band gap (i.e., direct or indirect), dielectric constant, and optical absorption, etc. We solvothermally synthesized wide band gap Pca21 phase pure BMO (≳3 eV) for two different pH values of 7 and 9. The structural parameters were correlated with the stability of BMO derived from elastic tensor simulations. The desired dynamical stability at T = 0 K was established from the phonon vibrational band structure using a finite difference-based supercell approach. The DFT-based Raman modes and phonon density of states (DOS) reliably reproduced the experimental Raman and infrared absorption. The electronic DOS calculated from Heyd-Scuseria-Ernzerhof HSE06 with van der Waals (vdW) and relativistic spin-orbit coupling (SOC) corrections produced a good agreement with the band gap obtained from diffuse reflectance spectroscopy (DRS). The optical absorption obtained from the complex dielectric constant for the HSE06+SOC+vdW potential closely resembled the DRS-derived absorption of BMO. The BMO shows ∼43% photocatalytic efficiency in degrading methylene blue dye under 75 min optical illumination. This combined DFT-experimental approach may provide a better understanding of the properties of BMO relevant to solar harvesting applications.

Enhancement of electrical conductivity and band gap of epoxy/MWCNT/GNP/glass fibers hybrid materials

Polymer composites containing carbon nanoparticles have attracted considerable attention because of their special functional characteristics. Characterization of optical and dielectric characteristics was done. To comprehend the impact of nanofillers, dielectric characteristics, UV–Vis spectroscopy, XRD, and Fourier transform spectroscopy were employed. The role of carbon fillers on metrics, such as band gap energy, absorption coefficient, and dielectric characteristics of nanocomposites was examined to differentiate between the effects of nanofillers. The AC conductivity is explained following the classical percolation theory. The percolation threshold is discovered to be 1 wt.% of a hybrid system of nanofillers consisting of graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (MWCNTs). The presence of carbon nanofillers significantly enhances the electrical conductivity of the nanocomposites. The optical band gap energy of nanocomposites was obtained from the Tauc method. The study establishes the relationship between band gap energy and AC conductivity using Tauc’s relation and Jonscher’s power law. The results show that the band gap energy of composites decreases with the addition of hybrid nanofillers, with values observed at 2.65 eV and 2.95 eV, while without fillers of 3.1 eV and 3.05 eV attributed to increased localized states within the bandgap. Composites with nanofillers show an AC conductivity of 1.86 S/m at 1 wt% of nanofillers, compared to 1.52 × 10−6 S/m and 1.09 × 10−6 S/m for composites without nanofillers. The UV–Vis spectra reveal a significant blue shift in the absorption peak when the weight percentage of carbon nanoparticles is increased. The findings of this study point toward the possibilities of the development of novel nanocomposites with enhanced performance for electronics and energy storage.

Tuning optical excitations of graphene quantum dots through selective nitrogen doping

Our research has revealed that the nitrogen doping configuration has a significant impact on the absorption properties and band gap of nitrogen doped graphene quantum dots (NGQDs). By analyzing the composition and character of optical transitions, we have observed that nitrogen doping causes a redistribution of oscillator strength between significant peaks and the emergence of new optical features. These changes lead to broken molecular orbital degeneracies, optical peak splitting, and activation of dark states in the visible to near-infrared (NIR) region. These findings shed light on the mechanisms that govern alterations in the spectral properties of NGQDs within the visible and near-infra red (NIR) absorption bands. Furthermore, selective manipulation of optoelectronic properties via distinct N-doping patterns could pave the way for the development of novel optoelectronic nanodevices and functional materials.

Nitrogen-rich carbon nitride with heptazine phase controlled by pyrolysis temperature towards photocatalytic U(VI) reduction

Photocatalytic process is a new and efficient technology, which has great potential in the U(VI) reduction process. Nitrogen is volatile at high temperatures, so its synthesis reaction is significantly influenced by pyrolysis temperature. Herein, a series of nitrogen-rich carbon nitride with different nitrogen content and different catalytic properties were prepared by changing the pyrolysis temperature from 450 °C to 650 °C. With the increase of pyrolysis temperature, the nitrogen content decreases continuously, and the triazine ring, tetrazine ring and azo bond generated by low temperature pyrolysis are gradually replaced by heptazine ring and nitrogen single bond. The nitrogen-rich carbon nitride synthesized at 550 °C has the best reducing activity for U(VI) reduction, which is attributed to the good cavity structure, narrow light absorption band gap and high electron transport channel. These results can provide guidance for regulating the electron transport structure of the nitrogen-rich carbon nitride to achieve enhanced photocatalytic activity.

(Invited) Electronic Trap Characterization in QD Devices Using Impedance Analysis Techniques

Colloidal quantum dots (QDs) are semiconductor nanocrystals with dimensions in the range of tens of nanometers. They exhibit unique optical and electronic properties, such as a size-dependent band gap and high absorption cross-section. These properties make them attractive for optoelectronic applications such as photovoltaics, light-emitting diodes (LEDs), and photodetectors. However, QD optoelectronics pose significant challenges due to trap states, which mainly originate from the surface states of nanocrystals. Therefore, it is necessary to analyze the trap states of QDs to understand their electronic properties and optimize their performance in optoelectronic applications. With this understanding, we want to correlate the cause of the trap states with the chemical defect to design better passivation strategies.In this discussion, we will explore the principles of electronic trap analysis in colloidal quantum dots based on impedance analysis techniques as a complementary method to spectroscopy. We will provide examples of electronic trap analysis in PbS QD photovoltaics and InP QD LEDs to demonstrate the effectiveness of this approach. We can electrically probe the QD layers in the device using an impedance analyzer to analyze the energy level and density of trap states. By combining chemical analysis and a theoretical approach with this technique, we attempted to correlate the trap states and chemical defects.

Broadband terahertz absorption and Q-switching behavior of 5-chloro-2-nitroaniline (5C2NA) crystals

Abstract Growth of transparent 5-chloro-2-nitroaniline (5C2NA) crystals was achieved through the slow evaporation technique. Analysis via X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy confirmed the crystalline nature of the organic crystals and revealing distinct molecular fingerprints of 5C2NA respectively. UV-VIS and Photoluminescence (PL) spectroscopy were employed to study the material's band gap and ground state absorption respectively. Thermogravimetric analysis (TGA) analysis indicated the stability of the grown crystals up to 211ºC. Dielectric measurements and Urbach plot suggested the presence of fewer defects in 5C2NA crystals. Time domain terahertz spectroscopy was utilized to observe the variation of absorption coefficient and refractive index in the terahertz frequency regime. Nonlinear optical effects such as saturable absorption (SA) and reverse saturable absorption (RSA), are pivotal in the development of all-optical logic gates. The transition between SA and RSA possesses a significant importance in optoelectronic applications. In this study, we investigate the 5C2NA crystal, revealing its ability to exhibit both SA and RSA under Z scan technique with varying pump intensities. The switching properties observed in 5C2NA can be harnessed for applications such as all-optical logic gates, rapid optical switching, optical limiting, mode storage, and more.