Investigation of Photoluminescence and Optoelectronics Properties of Transition Metal-Doped ZnO Thin Films.

Thin films of zinc oxide (ZnO) doped with transition metals have recently gained significant attention due to their potential applications in a wide range of optoelectronic devices. This study focuses on ZnO thin films doped with the transition metals Co, Fe, and Zr, exploring various aspects of their structural, morphological, optical, electrical, and photoluminescence properties. The thin films were produced using RF and DC co-sputtering techniques. The X-ray diffraction (XRD) analysis revealed that all the doped ZnO thin films exhibited a stable wurtzite crystal structure, showcasing a higher structural stability compared to the undoped ZnO, while the atomic force microscopy (AFM) imaging highlighted a distinctive granular arrangement. Energy-dispersive X-ray spectroscopy was employed to confirm the presence of transition metals in the thin films, and Fourier-transform infrared spectroscopy (FTIR) was utilized to investigate the presence of chemical bonding. The optical characterizations indicated that doping induced changes in the optical properties of the thin films. Specifically, the doped ZnO thin film's bandgap experienced a significant reduction, decreasing from 3.34 to 3.30 eV. The photoluminescence (PL) analysis revealed distinguishable emission peaks within the optical spectrum, attributed to electronic transitions occurring between different bands or between a band and an impurity. Furthermore, the introduction of these transition metals resulted in decreased resistivity and increased conductivity, indicating their positive influence on the electrical conductivity of the thin films. This suggests potential applications in solar cells and light-emitting devices.

Morphological, Photoluminescence, and Electrical Measurements of Rare-Earth Metal-Doped Cadmium Sulfide Thin Films.

This work is aimed at investigating the viability of utilizing cadmium sulfide (CdS) as a buffer layer in CdTe solar cells by analyzing and assessing its optical, photoluminescence, morphological, and electrical properties. These films were fabricated using a thermal coating technique. Optical microscopy was used to observe the changes in morphology resulting from the doping of rare-earth metals such as samarium (Sm) and lanthanum (La) to CdS, while the granular-like structure of the sample was confirmed by scanning electron microscopy. The objective of incorporating Sm and La ions into CdS was to enhance photoconductivity and optimize the optical bandgap, aiming to create a viable charge transport material for photovoltaic devices with enhanced efficiency. Through that process, a noticeable decrease in transmission, from approximately 80 to 68% in the visible region, was observed. Additionally, the bandgap value was reduced from 2.43 to 2.27 eV. Furthermore, during the analysis of the photoluminescence spectra, it was observed that emission peaks occurred in the visible region. These emissions were attributed to electronic transitions that took place via band-to-band and band-to-impurity interactions. The electrical measurements showed an enhancement in conductivity due to the decrease in the bandgap. This notable consequence of the doped materials suggests their utilization in photovoltaic systems.

Numerical optimization and performance evaluation of ZnPC:PC70BM based dye-sensitized solar cell.

The increase in global energy consumption and the related ecological problems have generated a constant demand for alternative energy sources superior to traditional ones. This is why unlimited photon-energy harnessing is important. A notable focus to address this concern is on advancing and producing cost-effective low-loss solar cells. For efficient light energy capture and conversion, we fabricated a ZnPC:PC70BM-based dye-sensitized solar cell (DSSC) and estimated its performance using a solar cell capacitance simulator (SCAPS-1D). We evaluated the output parameters of the ZnPC:PC70BM-based DSSC with different photoactive layer thicknesses, series and shunt resistances, and back-metal work function. Our analyses show that moderate thickness, minimum series resistance, high shunt resistance, and high metal-work function are favorable for better device performance due to low recombination losses, electrical losses, and better transport of charge carriers. In addition, in-depth research for clarifying the impact of factors, such as thickness variation, defect density, and doping density of charge transport layers, has been conducted. The best efficiency value found was 10.30% after tweaking the parameters. It also provides a realistic strategy for efficiently utilizing DSSC cells by altering features that are highly dependent on DSSC performance and output.

A Study of the Structural and Surface Morphology and Photoluminescence of Ni-Doped AlN Thin Films Grown by Co-Sputtering.

Aluminum nitride (AlN) is a semiconductor material possessing a hexagonal wurtzite crystal structure with a large band gap of 6.2 eV. AlN thin films have several potential applications and areas for study, particularly in optoelectronics. This research study focused on the preparation of Ni-doped AlN thin films by using DC and RF magnetron sputtering for optoelectronic applications. Additionally, a comparative analysis was also carried out on the as-deposited and annealed thin films. Several spectroscopy and microscopy techniques were considered for the characterization of structural (X-ray diffraction), morphological (SEM), chemical bonding (FTIR), and emission (PL spectroscopy) properties. The XRD results show that the thin films have an oriented c-axis hexagonal structure. SEM analysis validated the granular-like morphology of the deposited sample, and FTIR results confirm the presence of chemical bonding in deposited thin films. The photoluminescence (PL) emission spectra exhibit different peaks in the visible region when excited at different wavelengths. A sharp and intense photoluminescence peak was observed at 426 nm in the violet-blue region, which can be attributed to inter-band transitions due to the incorporation of Ni in AlN. Most of the peaks in the PL spectra occurred due to direct-band recombination and indirect impurity-band recombination. After annealing, the intensity of all observed peaks increases drastically due to the development of new phases, resulting in a decrease in defects and a corresponding increase in the crystallinity of the thin film. The observed structural, morphological, and photoluminescence results suggest that Ni: AlN is a promising candidate to be used in optoelectronics applications, specifically in photovoltaic devices and lasers.

Tailoring TiO2/Al2O3 heterolayers as optical filters for the visible region.

Optical filters operating in the visible region of the spectrum are highly desired for applications ranging from optical communication and sensing to fluorescence microscopy and skin therapy. However, complex fabrication procedures and/or inferior performance, limit the practical applications of previously reported thin-film-based optical filters. Herein, we describe the structual design concepts and facile fabrication of vertically stacked heterolayers of TiO2/Al2O3 to obtain a bandpass filter and a longwave pass edge filter operating in the spectral range 410-600 nm and 400-597 nm, respectively. The optical filters are designed according to MacLeod simulation and fabricated via magnetron sputtering, depositing alternative stacks of low (Al2O3) and high (TiO2) refractive index materials with different thicknesses, as confirmed by spectroscopic ellipsometry. Owing to a reasonable matching between the design and the fabrication, our developed TiO2/Al2O3 heterolayer optical filters exhibited 54.60% transmission for 7-layer longwave pass edge filter and 15% reflectance for 14-layer bandpass filter of a selective set of wavelengths (400-800 nm).

A Cross-Sectional Evaluation of Vitamin D Status and Ovarian Reserve Markers in Subfertile Women: A Single-Center Experience From Pakistan.

Objectives This study was conceived with the objective of assessing the correlation between ovarian reserve markers and vitamin D deficiency (VDD) in a selected group of Pakistani subfertile women presenting at a specialized subfertility treatment centre. The measurements of antral follicle count (AFC), serum anti-Müllerian hormone (AMH), serum follicle-stimulating hormone (FSH), and serum vitamin D (VD) levels were the main tools used for the assessment of ovarian reserve. Materials and methods All female patients aged 18 to 45 years presenting with primary and/or secondary subfertility at the Australian Concept Medical Centre in Karachi, Pakistan from August 2016 to July 2021 were included in the study. The data of all eligible patients were recorded in the pre-defined Performa designed for this study. The Kruskal-Wallis test was applied to report the distribution of the data. The correlation between the categorical variables (25-hydroxyvitamin D [25-OHD] levels with AFC and AMH) was assessed using the chi-square test and Spearman correlation. The comparison was based on vitamin D levels grouped into three categories: deficiency (<20 ng/ml), insufficiency (21-29 ng/ml), and sufficiency (>30 ng/ml). Results One hundred ninety-nine cases were evaluated for AFC and hormone analysis. The mean age and BMI were 32.87±5.49 years and 28.27±4.97 kg/m2.VDD was noted in 127 (68.4%) cases. No significant difference was noted across BMI, age, duration of subfertility, AMH, and FSH across the VD categories. Moreover, a poor correlation was noted between VD, AMH and FSH on the scatter plot, between VD and FSH (r = -0.003, p = 0.966) and between VD and AMH (r = -0.068, p = 0.342), respectively. Conclusions This study showed a high frequency of VDD in Pakistani subfertile women, from a specialized subfertility center in the largest metropolis in the country. However, a statistically significant association was not found between the markers of ovarian reserve and VD, showing no ethnic differences in the native Pakistani population. Hence, VD supplementation is unlikely to have an impact on correcting the ovarian reserve status in subfertile women in Pakistan. However, this is a potential area of interest, and evaluation of other indices of reproduction/ovarian reserve and the effect of confounders is required to test this hypothesis longitudinally.