Search Results (7)

The search for stable, lead-free perovskite materials is critical for developing efficient and environmentally friendly energy solutions. In this study, machine learning methods were applied to predict the bandgap and formation energy of double perovskites, aiming to identify promising photovoltaic candidates. A dataset of 1053 double perovskites was extracted from the Materials Project database, with 50 feature descriptors generated. Feature selection was carried out using Pearson correlation and mRMR methods, and 23 key features for bandgap prediction and 18 key features for formation energy prediction were determined. Four algorithms, including gradient-boosting regression (GBR), random forest regression (RFR), LightGBM, and XGBoost, were evaluated, with XGBoost demonstrating the best performance (R² = 0.934 for bandgap, R² = 0.959 for formation energy; MAE = 0.211 eV and 0.013 eV/atom). The SHAP (Shapley Additive Explanations) analysis revealed that the X-site electron affinity positively influences the bandgap, while the B″-site first and third ionization energies exhibit strong negative effects. Formation energy is primarily governed by the X-site first ionization energy and the electronegativities of the B′ and B″ sites. To identify optimal photovoltaic materials, 4573 charge-neutral double perovskites were generated via elemental substitution, with 2054 structurally stable candidates selected using tolerance and octahedral factors. The XGBoost model predicted bandgaps, yielding 99 lead-free double perovskites with ideal bandgaps (1.3~1.4 eV). Among them, four candidates are known compounds according to the Materials Project database, namely Ca₂NbFeO₆, Ca₂FeTaO₆, La₂CrFeO₆, and Cs₂YAgBr₆, while the remaining 95 candidate perovskites are unknown compounds. Notably, X-site elements (Se, S, O, C) and B″-site elements (Pd, Ir, Fe, Ta, Pt, Cu) favor narrow bandgap formation. These findings provide valuable guidance for designing high-performance, non-toxic photovoltaic materials. Full article

Cu-based ternary oxides with delafossite structure have received considerable attention in recent years for their versatility in a wide range of applications, among which is the possibility to use them in heterostructure solar cells as hole transport layers, due to their promising behavior as p-type conducting oxides. Ab initio calculations have been performed with density functional theory to investigate the role of the trivalent metal within the CuMO₂ structure and the dependence of structural and electronic properties with the species (M = Al, Ga, In, Fe, Cr, Co, Sc, Y) occupying the site of the metal. Generalized Gradient Approximation also including a Hubbard term and nonlocal Heyd–Scuseria–Enzerhof screened hybrid functional schemes were tested and their results were compared. Excellent agreement with experimental lattice parameters and measured gaps have been found. The use of hybrid functionals in HSE approximation considerably improves the bandgaps when compared with the experimental results but takes considerable time to converge, hence the need to explore less demanding methodologies. Trends in the geometry as well as in the electronic properties are discussed, and the effect of mixing different metals (CuM_xN_1−xO₂, M, N being the aforementioned elements) in the geometry and electronic properties of these delafossite materials is investigated. Due to the high cost of HSE calculations, especially when supercells are needed to model several x concentrations, statistical models and techniques based on machine learning have also been explored to predict HSE bandgap values from GGA and structural information. Full article

For the first time, the effect of Cuprous Oxide (Cu₂O) sputtering power variation on the radio frequency sputtered Copper Chromium Oxide (CuCrO₂) thin films was studied. In this work, the sputtering power of Cr₂O₃ was held constant at 200 W while the sputtering power of the Cu₂O target was varied from 10 to 100 W. The films were subsequently annealed at 650 °C in N₂ ambiance. The effects of Cu₂O sputtering power variation on the structural, optical, and electrical properties of the films have been reported in this work. X-ray diffractometer (XRD) study revealed that the single-phase delafossite structure of CuCrO₂ was only obtained at Cu₂O sputtering power of 50 W. X-ray photoelectron spectroscopy (XPS) analysis further established the results of XRD study where Cu in 1+ oxidation state was identified in thin films obtained at 50 W of Cu₂O sputtering power. The optical studies were conducted in this work on all the post-deposition annealed films in the wavelength range of 200–800 nm. The energy dispersive x-ray spectroscopy (EDS) study revealed a near stoichiometric composition ratio of 1:1.06 of Cu:Cr at% obtained in the films sputtered with 50 W of Cu₂O sputtering power. The highest optical transmission of ~81% and the highest optical bandgap of 3.21 eV were observed for single-phase CuCrO₂ thin films. The optical transmission and the optical bandgap were found to decrease with an increase in the Cu₂O sputtering power. The electrical study performed on all the post-deposition annealed films revealed that the lowest resistivity of 0.652 Ω-cm was identified for single-phase CuCrO₂ thin films obtained at 50 W of Cu₂O sputtering power. Full article

For the first time, the deposition of CuCrO₂ thin films was carried out using a dual-target RF magnetron sputtering technique using Cu₂O and Cr₂O₃ targets. The deposited films were subsequently annealed in N₂ ambiance from 600–900 °C. This work reports that the electrical, optical, structural, and morphological properties of CuCrO₂ thin films are significantly affected due to the variation in the annealing temperature. XRD analysis confirms the presence of single-phase CuCrO₂ in the films annealed at 650 °C. The presence of Cu in the 1+ oxidation state in the phase pure CuCrO₂ thin films was confirmed through XPS analysis. Further, through XPS analysis, the oxidation states of Cu and Cr, the full-width half maximum (FWHM), the peak positions, and their respective binding energies have been elucidated. SEM analysis confirms the promotion of nanocrystalline growth in the thin films as the annealing temperature was increased from 600 °C. The average grain size increased from 40.22 nm to 105.31 nm as the annealing temperature was increased from 600 to 900 °C. Optical studies conducted in the wavelength range of 200 nm to 800 nm revealed a decrease in the optical transmission and optical bandgap with an increase in the annealing temperature. The highest optical transmission of ~81% and an optical bandgap of 3.21 eV were obtained for the films depicting the delafossite nature of CuCrO₂. The optical bandgap was found to vary between 3.16 eV and 3.74 eV for the films studied in this research. The lowest resistivity of 0.652 Ω cm was obtained for the films annealed at 650 °C. Transparent heterojunction diodes involving p-type delafossite copper chromium oxide (CuCrO₂) and n-type indium tin oxide (ITO) were fabricated. The best diode depicted a cut-in voltage of 0.85 V, a very low leakage current of 1.24 x 10-8, an ideality factor of 4.13, and a rectification ratio of 2375. Full article

The magnetic, optical, and phonon properties of ion-doped CuAlO${}_2$ nanoparticles on the Cu or Al site are theoretically investigated. The room temperature ferromagnetism in CuAlO${}_2$ nanoparticles can be due to the surface, size, and doping effects. The magnetization increases with the decreasing nanoparticle size. The different radii of the transition metal ion and the host Cu ion lead to compressive strain, to the enhancment of the exchange interaction constants, and to increased magnetization $M_s$ and Curie temperature $T_C$. By substitution with Mn or Cr on the Al site, tensile strain, a decrease in $M_s$, and an increase in dopants are observed. The size and ion-doping influence on the band-gap energy is also discussed. The phonon energy $\omega$ decreases, whereas the phonon damping $\gamma$ increases with increasing temperature and decreasing NP size. They show a kink around $T_C$ ∼ 400 K. The behavior of $\omega$ and $\gamma$ for different ion dopings is observed. Full article

The performance and stability in atmospheric conditions of organic photovoltaic devices can be improved by the integration of stable and efficient photoactive materials as substituent of the chemically unstable poly (3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS), generally used as organic hole transport layer. Promising candidates are p-type transparent conductive oxides, which combine good optoelectronic and a higher mechanical and chemical stability than the organic counterpart. In this work, we synthesize Cu-rich CuCrO₂ thin films by aerosol-assisted chemical vapour deposition as an efficient alternative to PEDOT:PSS. The effect of stoichiometry on the structural, electrical, and optical properties was analysed to find a good compromise between transparency, resistivity, and energy bands alignment, to maximize the photovoltaic performances., Average transmittance and bandgap are reduced when increasing the Cu content in these out of stoichiometry CuCrO₂ films. The lowest electrical resistivity is found for samples synthesized from a solution composition in the 60–70% range. The optimal starting solution composition was found at 65% of Cu cationic ratio corresponding to a singular point in Hackee’s figure of merit of 1 × 10⁻⁷ Ω⁻¹. PBDD4T-2F:PC₇₀BM organic solar cells were fabricated by integrating CuCrO₂ films grown from a solution composition ranging between 40% to 100% of Cu as hole transport layers. The solar cells integrating a film grown with a Cu solution composition of 65% achieved a power conversion efficiency as high as 3.1%, representing the best trade-off of the optoelectronic properties among the studied candidates. Additionally, despite the efficiencies achieved from CuCrO₂-based organic solar cells are still inferior to the PEDOT:PSS counterpart, we demonstrated a significant enhancement of the lifetime in atmospheric conditions of optimal oxides-based organic photovoltaic devices. Full article

This paper deals with the study of the optical properties of one-dimensional SrTiO₃/PAN-based photocatalysts with the addition of metal oxide particles and the determination of their bandgaps. One-dimensional photocatalysts were obtained by the electrospinning method. Particles of metals such as iron, chromium, and copper were used as additives that are capable of improving the fibers’ photocatalytic properties based on SrTiO₃/PAN. The optimal ratios of the solutions for the electrospinning of fibers based on SrTiO₃/PAN with the addition of metal oxide particles were determined. The transmission and reflection of composite photocatalysts with metal oxide particles were measured in a wide range of spectra, from the ultraviolet region (185 nm) to near-infrared radiation (3600 nm), to determine the values of their bandgaps. Thus, the introduction of metal oxide particles resulted in a decrease in the bandgaps of the obtained composite photocatalysts compared to the initial SrTiO₃/PAN (3.57 eV), with the following values: −3.11 eV for SrTiO₃/PAN/Fe₂O₃, −2.84 eV for SrTiO₃/PAN/CuO, and −2.89 eV for SrTiO₃/PAN/Cr₂O₃. The obtained composite photocatalysts were tested for the production of hydrogen by the splitting of water–methanol mixtures under UV irradiation, and the following rates of hydrogen evolution were determined: 344.67 µmol h⁻¹ g⁻¹ for SrTiO₃/PAN/Fe₂O₃, 398.93 µmol h⁻¹ g⁻¹ for SrTiO₃/PAN/Cr₂O₃, and 420.82 µmol h⁻¹ g⁻¹ for SrTiO₃/PAN/CuO. Full article