Camellia Doroody

An in-depth examination was undertaken on the structural, optical, and electrical alterations of CdTe thin films exposed to CuCl₂ post-treatment with different molar concentrations. The films were prepared using the close-spaced sublimation (CSS) approach. The CuCl₂ treatment at 390 °C in ambient air had significant impacts on the crystallographic orientation, lattice properties, and carrier concentration of CdTe films. The full width at half maximum (FWHM) increased from 0.0038 radians at 0.0005 M CuCl₂ to 0.0068 radians at 0.05 M, indicating grain refinement and increased microstrain at higher Cu concentrations, confirming a significant zincblende (111) preferred orientation as the X-ray diffraction (XRD) research reported. The inclusion of Cu and the resulting lattice deformation demonstrate a significant relationship with the evolution of crystallite size and dislocation density, indicating a regulated interaction between the dopant and the lattice throughout the examined molarity range. A comprehensive evaluation of structural, optical, morphological, and electrical properties indicates that a CuCl₂ concentration of 0.005 M achieves an optimal balance, facilitating effective p-type activation while preventing excessive Cu diffusion, which is associated with increased microstrain, decreased mobility, and heightened recombination at elevated dopant concentrations. XRD analysis confirms the retention of zincblende crystallinity without the formation of secondary phases, while optical measurements demonstrate stable band-gap behaviour, indicating minimal electronic distortion. Complementary FESEM and EDX analyses reveal enhanced grain coalescence and a reduction in grain-boundary density, which together facilitate improved carrier transport. The synergistic enhancements position the CuCl₂ solution-based treatment, especially at 0.005 M, as an effective and environmentally friendly alternative to traditional CdCl₂ activation, directly influencing the formation of ohmic contacts and the performance of CdTe thin-film.

The synthesis of superior, thickness-regulated molybdenum disulfide (MoS ₂ ) films using vapor-phase growth is a formidable challenge in two-dimensional (2D) materials research. In this study, we comprehensively investigated the synthesis of MoS ₂ films through sulfurization in a furnace with quartz tubes. By varying the sulfurization time from 10 to 60 minutes, we precisely controlled how thick the MoS ₂ films were. Raman spectroscopy revealed a distinctive difference in the creation of a monolayer, which is indicated by the 19.12 cm ⁻¹ gap between the in-plane (E12g) and out-of-plane (A1g) vibration peaks, indicating the formation of monolayer MoS ₂ . The surface morphology and crystallization processes of multilayer MoS ₂ films were described using scanning electron microscopy and atomic force microscopy, unveiling the influence of synthesis parameters. Notably, synthesis at low temperatures (480 °C) exhibited broader Raman peaks, signifying poor crystallinity, while higher temperatures (550 °C) yielded narrow peaks, indicating superior crystallinity. Optimized synthesis conditions at 550 °C and a pressure of 1 KPa facilitated the production of continuous, uniform, and fully covered MoS ₂ films. Furthermore, the introduction of sulfur content in the precursor solution enhanced the crystal quality, as evidenced by narrower Raman peak line widths and distinct absorption peaks at 614 nm and 665 nm. Our findings underscore the importance of sulfurization parameters in tailoring the crystallinity and thickness control of MoS ₂ films, offering significant potential for improved sustainability and performance in solar energy-related applications.

The critical impact of sodium-doped molybdenum (MoNa) in shaping the MoSe₂ interfacial layer, influencing the electrical properties of CIGSe/Mo heterostructures, and achieving optimal MoSe₂ formation conditions, leading to improved hetero-contact quality. Notably, samples with a 600-nm-thick MoNa layer demonstrate the highest resistivity (73 μΩcm) and sheet resistance (0.45 Ω/square), highlighting the substantial impact of MoNa layer thickness on electrical conductivity. Controlled sodium diffusion through MoNa layers is essential for achieving desirable electrical characteristics, influencing Na diffusion rates, grain sizes, and overall morphology, as elucidated by EDX and FESEM analyses. Additionally, XRD results provide insights into the spontaneous peeling-off phenomenon, with the sample featuring a ~ 600-nm MoNa layer displaying the strongest diffraction peak and the largest crystal size, indicative of enhanced Mo to MoSe₂ conversion facilitated by sodium presence. Raman spectra further confirm the presence of MoSe₂, with its thickness correlating with MoNa layer thickness. The observed increase in resistance and decrease in conductivity with rising MoSe₂ layer thickness underscore the critical importance of optimal MoSe₂ formation for transitioning from Schottky to ohmic contact in CIGSe/Mo heterostructures. Ultimately, significant factors to the advancement of CIGSe thin-film solar cell production are discussed, providing nuanced insights into the interplay of MoNa and MoSe₂, elucidating their collective impact on the electrical characteristics of CIGSe/Mo heterostructures. Graphical Abstract

A numerical analysis of a CdTe/Si dual-junction solar cell in terms of defect density introduced at various defect energy levels in the absorber layer is provided. The impact of defect concentration is analyzed against the thickness of the CdTe layer, and variation of the top and bottom cell bandgaps is studied. The results show that CdTe thin film with defects density between 10¹⁴ and 10¹⁵ cm⁻³ is acceptable for the top cell of the designed dual-junction solar cell. The variations of the defect concentrations against the thickness of the CdTe layer indicate that the open circuit voltage, short circuit current density, and efficiency (ƞ) are more affected by the defect density at higher CdTe thickness. In contrast, the Fill factor is mainly affected by the defect density, regardless of the thin film’s thickness. An acceptable defect density of up to 10¹⁵ cm⁻³ at a CdTe thickness of 300 nm was obtained from this work. The bandgap variation shows optimal results for a CdTe with bandgaps ranging from 1.45 to 1.7 eV in tandem with a Si bandgap of about 1.1 eV. This study highlights the significance of tailoring defect density at different energy levels to realize viable CdTe/Si dual junction tandem solar cells. It also demonstrates how the impact of defect concentration changes with the thickness of the solar cell absorber layer.