Inverted organic cells are promising devices for sustainable and low-cost future electric generation. In this work, we present the degradation mechanisms studied in ITO/TiO 2 /PTB7:PC 70 BM/V 2 O 5 /Ag inverted organic solar cells (iOSCs) by impedance spectroscopy (IS). Measurements were performed on encapsulated (controlled environment) and nonencapsulated (ambient condition) cells following their temporal evolution under AM1.5 illumination for several voltage biases. From the impedance spectra, analyzed in terms of resistive/capacitive equivalent circuits, we were able to identify that the most sensitive layers inside of the device are contact layers. According with presented, IS technique is useful for determining the materials that have more influence on the degradation of organic solar cells. We demonstrate that IS is a powerful technique to identify the limiting mechanisms and to establish the limiting materials inside of the iOSCs.

SummaryThis work presents a novel technique to deposit ZnO thin films through a metal vacuum evaporation technique using colloidal nanoparticles (average size of 30 nm), which were synthesized by our research group, as source. These thin films had a thickness between 45 and 123 nm as measured by profilometry. XRD patterns of the deposited thin films were obtained. According to the HRSEM micrographs worm-shaped nanostructures are observed in samples annealed at 600 °C and this characteristic disappears as the annealing temperature increases. The films obtained were annealed from 25 to 1000 °C, showing a gradual increase in transmittance spectra up to 85%. The optical band gaps obtained for these films are about 3.22 eV. The PL measurement shows an emission in the red and in the violet region and there is a correlation with the annealing process.

ZnO colloidal nanoparticles were synthesized, the average size of these nanoparticles is around 25 nm with hexagonal form. It was noted that stabilization depends directly on the purifying process; in this work we do not change the nature of the solution as a difference from Meulekamp's method, and we do not use any alkanes to remove the byproducts; only a centrifuge to remove those ones was used, thereby the stabilization increases up to 24 days. It is observed from the results that only three times of washing is enough to prevent the rapid aging process. The effect of annealing process on the composition, size, and geometrical shape of ZnO nanoparticles was studied in order to know whether the annealing process affects the crystallization and growth of the nanoparticles. After the synthesis, the colloidal nanoparticles were deposited by spin coating technique showing that the formed nanoparticles have no uniformly deposition pattern. But is possible to deposit those ones in glass substrates. A possible deposition process of the nanoparticles is proposed.

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Lead selenide nanoparticles (PbSe NPs) have been obtained through an easy and low cost route using colloidal synthesis in aqueous solution. The synthesis was carried out at room temperature using Extran (Na₅P₃O₁₀, NaOH and H₂O) as surfactant. Hydrochloric acid (HCl) was used to eliminate the generated by-products. The size of PbSe NPs was varied by changing the Pb:Se molar concentration. The PbSe NPs were characterized by powder x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDAX), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. The XRD measurements showed that the PbSe NPs have the face-centered cubic phase structure. The crystal size was found to be between 14 and 20 nm as calculated from the XRD patterns and these values were corroborated with SEM and TEM. Additionally, HRTEM micrographs showed crystalline planes at (200), (220) and (111) of the PbSe NPs, in agreement with the XRD results.

In this study, we report the effect of ZnO film thickness on its optical and structural properties. The sol solution was synthesized by sol-gel method and deposited on silicon substrates by spin coating technique. The ZnO films thickness was varied from 60 to 180 nm. The ZnO films obtained showed a highly preferred orientation along the (002) plane. It was also observed that the crystallite size was not affected by increasing thickness. Transmittance measurements indicated that the ZnO films have a high transparency in the visible range (~90 %), which remained constant with thickness. Morphological evolution measurements confirmed that the thinner ZnO film consist mostly of a porous layer which became homogeneous and compact to increase the thickness. Photoluminescence measurements exhibit a strong ultraviolet (UV) emission, and the emission intensity was improved with thickness due to crystallinity enhancement.

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SiO 2 films by atmospheric pressure chemical vapor deposition (APCVD) process, using tetraethoxysilane (TEOS) and ozone (O 3 ) as reactant were obtained. The films were deposited on silicon substrates at various temperatures 125, 150, 175, 200, 225 and 250 °C Fourier transforms infrared (FTIR) spectroscopy was used to characterize the SiO 2 films. Absorbance spectrums show the vibration modes corresponding to SiO 2 films. Additional absorption bands due to residual groups were also observed, but they were found to be dependent on the deposition temperature. The observed current flowing through the oxide could be related to these residual groups, mainly to hydroxyl groups.