Sandra. A. Mayen Hernández

This work investigates a non-polluting alternative for activation treatment, consisting of using a saturated solution of MgCl2 in methanol. For this research, three types of solar cells were analyzed: without activation treatment, activation with CdCl2 deposited by sublimation in a closed space, and activation with a saturated solution of MgCl2 by immersion. The solar cells were characterized using several techniques: scanning electron microscopy images were analyzed to show how the grains of the CdTe layer changed after the activation treatment; using the data obtained through a solar simulator, improvements were observed in Voc, Jsc, and FF; efficiency η increased from 4.4% without activation to 11.92% when MgCl2 is used and to 7.42% with CdCl2; these results were contrasted through numerical simulation based on SCAPS-1D software. We propose that the CdS/CdTe heterojunction becomes thinner during activation due to diffusion between these films; in this way, the film thickness and doping concentration depend on the activation treatment. Finally, we demonstrate that the device can be activated with MgCl2, achieving a maximum efficiency of 11.92%; with values of 760 mV, 27.02 mA/cm2 and 0.58 of the Voc, Jsc, and FF respectively.

Herein, the influence of Mg-doped CdS nanocrystals (NCs) on the performance of hybrid solar cells (HSCs) is investigated for the first time. Pristine and Mg-doped CdS NCs at different concentrations (0.25, 0.5, and 0.75 mol%) are synthesized using the heating up method. The effect of Mg on structural, compositional, morphological, optical, and electrical properties of CdS NCs is examined. The structural analysis showed a peak shift toward a higher wavelength, while lattice parameters a and c are decreased. As the Mg concentration increases, the shape and size of the CdS NCs are considerably changed, while the bandgap is tuned from 2.66 to 2.44 eV. Besides, the resistivity of CdS is significantly decreased while carrier concentration increases. Then, the device is fabricated with a configuration of FTO/TiO₂/P3HT:PC₆₁BM/MoO₃/Ag, wherein the influence of different concentrations of undoped and Mg-doped CdS NCs on the performance of HSCs is explored. The Mg-doped CdS NCs exhibited a power conversion efficiency of 2.92%, 2.5 times higher than the polymer device. Thus, the results revealed that the Mg doping significantly improved the properties of CdS NCs and the performance of HSCs. Henceforth, this work would provide a new path to enhance the power conversion efficiency of the HSCs in a low-cost approach.

Antimony sulfide thin films were deposited on glass substrates at room temperature by pulsed laser deposition using pellets of Sb2S3 as the target. The structural characterization showed that the as-grown films have a high amorphous contribution, and the annealed samples have the Sb2S3 orthorhombic phase. The values for the calculated crystal sizes of 27, 25, and 26 nm for the annealing temperatures of 250, 275, and 300 °C, respectively, for the case of transmission for the as-grown sample amount to 30%, while for the annealed samples, the value is less than 10%. In the reflection measurements, the as-grown sample and the one annealed at 250 °C present lower values at 10%, while for the samples annealed at 275 and 300 °C, the reflection values are between 25% and 35%. On the other hand, the bandgap through the Tauc’s parabolic band method was calculated, with its value for the as-grown sample being 1.92 eV, while for the samples annealed at 250, 275, and 300 °C, the bandgap values are 1.31, 1.66, and 1.29 eV, respectively. The atomic percentage determined by Energy Dispersive Spectroscopy was 36% Sb and 64% S for the as-grown sample, while for the annealed samples, the percentage of sulfur increases, and the percentage of antimony decreases until a final value of 30.5% Sb and 69.5% S for the sample annealed at 300 °C.

Yttrium oxide nanostructures doped with erbium and ytterbium ions were incorporated into a titanium dioxide (TiO₂) host by a hydrothermal method to modify the bandgap of TiO₂. The samples were prepared with different concentrations of nanophosphors (Y₂O₃: Er³⁺-Yb³⁺). Then, the samples were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), x-ray photoelectron spectroscopy (XPS), and photoluminescence spectroscopy. The XRD analysis revealed the mixture of anatase and rutile crystal structures for all the samples. The TEM measurements showed agglomerated particles with a spherical shape of around 50 nm. TiO₂ doped with a high concentration of Y₂O₃:Er³⁺-Yb³⁺ exhibited a strong visible upconversion luminescence under the excitation of 980 nm (infrared laser) as compared to other samples. Photoluminescence studies revealed the green (522 nm), yellow (563 nm), and red emissions (661 nm) corresponding to ²H_11/2→ ⁴I_15/2, ⁴S_3/2→ ⁴I_15/2, and ⁴F_9/2→ ⁴I_15/2 transitions of Er³⁺ in Y₂O₃:Er³⁺-Yb³⁺@TiO₂ nanophosphors, respectively. Furthermore, DRS and XPS analyses revealed that Y₂O₃:Er³⁺-Yb³⁺ modified the bandgap of the TiO₂ host.

Titanium dioxide (TD) and graphene oxide (GO) were synthesized by sol-gel and improved Hummers method, respectively. This study shows the results of the incorporation through four different conditions (sol-gel, sol-gel and ultrasonic, annealed, and UV radiation, C1 to C4, respectively). It was observed that a homogeneous incorporation of TD on sheets of GO was obtained satisfactorily. The composites of TiO₂/GO were characterized using different techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy, and infrared spectroscopy (IR). The photocatalytic activity of the composites was determined from the degradation of the dye azo tartrazine using UV and solar radiation. The best incorporation of TD nanoparticles on GO was obtained with condition C3 (thermal incorporation method) at a temperature of 65°C. This shows a uniformity in the size and shape of the TD as well as an excellent adherence to the sheet of GO. This addition is accomplished by ionic bonding in the presence of electrostatic Coulomb forces. The C3 composite degraded the tartrazine dye using UV radiation and sunlight. With the latter, the degradation time was three times faster than using UV light.