Crystal Chemistry, Optical–Electronic Properties, and Electronic Structure of Cd_1–xIn_2+2x/3S₄ Compounds (0 ≤ x ≤ 1), Potential Buffer in CIGS-Based Thin-Film Solar Cells

Abstract

CdIn2S4 and In2S3 compounds were both previously studied as buffer layers in CIGS-based thin-film solar cells, each of them exhibiting advantages and disadvantages. Thus, we naturally embarked on the study of the CdIn2S4–In2S3 system, and a series of Cd1–x In2+2x/3S4 (0 ≤ x ≤ 1) materials were prepared and characterized. Our results show that two solid solutions exist. The aliovalent substitution of cadmium­(II) by indium­(III) induces a structural transition at x ≈ 0.7 from cubic spinel Fd3̅m to tetragonal spinel I41/amd that is related to an ordering of cadmium vacancies. Despite this transition, the variation of optical gap is continuous and decreases from 2.34 to 2.11 eV going from CdIn2S4 to In2S3 while all compounds retain an n-type behavior. In contrast with the Al x In2‑xS3 solid solution, no saturation of the gap is observed. Moreover, XPS analyses indicate a difference between surface and volume composition of the grains for Cd-poor compounds. The use of Cd1–x In2+2x/3S4 compounds could be a good alternative to CdIn2S4 and In2S3 to improve CIGS/buffer interfaces with a compromise between photovoltaic conversion efficiency and cadmium content.

Photocatalytic Mechanism Control and Study of Carrier Dynamics in CdS@C3N5 Core–Shell Nanowires

“…The 113 Cd magic-angle spinning (MAS) NMR spectra (Bloch pulse) of the pristine CdS, CdS-MHP, and CdS-MHPINS samples are shown in Figure a. CdS and CdS-MHP samples yield 113 Cd NMR spectra containing a single symmetric peak at δ iso ≈ 706 ppm with FWHM values ranging from 670 to 760 Hz; these are assigned to 113 Cd nuclei with symmetric tetrahedral coordination of four neighboring S atoms and are attributed to core Cd nuclei. − The chemical shifts exhibited by these samples are similar to those previously reported for nanoparticle (δ iso = 719 ppm) and bulk (δ iso = 687 ppm) CdS. − The 113 Cd NMR spectrum for CdS-MHPINS shows a significantly broader and asymmetric peak with a more intense resonance located at 707 ppm (FWHM = ∼1 kHz) and a less intense broader resonance at ∼723 ppm (FWHM ∼2 kHz). The broader resonance at ∼723 ppm suggests a less ordered local cadmium chemical environment (Cd coordinated with 4 S atoms in a pseudo-tetrahedral environment) in the presence of MHPINS, which is consistent with the XPS data that revealed similar Cd–S bonding environments in CdS-MHP and CdS-MHPINS samples discussed earlier.…”

Optoelectronic Properties of TiS2: A Never Ended Story Tackled by Density Functional Theory and Many-Body Methods

“…In order to get a picture closer to the experimental one to ensure a more realistic comparison, a moving average was applied. 52,65 Such a data post-treatment of the nth order on a given signal (s 1 , ..., s N ) consists of averaging each value with the n − 1 previous points, resulting into a smoother signal. Mathematically, the pth value of the smoothed signal s p ′ can be written as…”

“…The only calculations reported in Figure are the ones including dispersion effects because it has been proven above that they are necessary to explain the structural behavior of the compound of interest. In order to get a picture closer to the experimental one to ensure a more realistic comparison, a moving average was applied. , Such a data post-treatment of the n th order on a given signal (s 1 , ..., s N ) consists of averaging each value with the n – 1 previous points, resulting into a smoother signal. Mathematically, the p th value of the smoothed signal s p ′ can be written as The four curves were aligned horizontally on their maximum and normalized.…”

Femtosecond Laser Fabrication of Micro and Nano-Structures on CIGS/ITO Bilayer Films for Thin-Film Solar Cells

“…CIGS films are direct band-gap semiconductors having an absorption coefficient of up to 10 5 cm −1 and an absorption thickness of 1–2 μm [ 5 ]. Currently, most investigations focus on improving the photoelectric conversion efficiency of the CIGS solar cells by adjusting the material composition or optimizing thin-film preparation technology [ 6 , 7 , 8 , 9 ]. Different fabrication methods (e.g., co-evaporation, continuous evaporation, sputtering, vacuum evaporation, and spray pyrolysis [ 10 , 11 , 12 , 13 , 14 ]) can modify the elemental composition of the films, thus affecting surface particle size and absorptivity.…”