Influence of a Compact Fe2O3 Layer on the Photovoltaic Performance of Perovskite-Based Solar Cells

[EN] In this study, uniform and dense iron oxide ¿-Fe2O3 thin films were used as an electron-transport layer (ETL) in CH3NH3PbI3-based perovskite solar cells (PSCs), replacing the Titanium dioxide (TiO2) ETL conventionally used in planar heterojunction perovskite solar cells. The ¿-Fe2O3 films were synthesized using an electrodeposition method for the blocking layer and a hydrothermal method for the overlaying layer, while 2,2¿,7,7¿-tetrakis (N, N¿-di-p-methoxyphenylamine)-9,9¿ spirobifluorene (spiro-OMeTAD) was employed as a hole conductor in the solar cells. Based on the above synthesized ¿-Fe2O3 films the photovoltaic performance of the PSCs was studied. The ¿-Fe2O3 layers were found to have a significant impact on the photovoltaic conversion efficiency (PCE) of the PSCs. This was attributed to an efficient charge separation and transport due to a better coverage of the perovskite on the ¿-Fe2O3 films. As a result, the PCE measured under standard solar conditions (AM 1.5G, 100 mW cm¿2) reached 5.7%.This work was supported by the Ministry of High Education and Scientific Research, Tunisia and Ministerio de Economia y Competitividad (ENE2013-46624-C4-4-R) and Generalitatvalenciana (Prometeus 2014/044).Bouhjar, F.; Mollar García, MA.; Ullah, S.; Marí, B.; Bessais, B. (2018). Influence of a Compact Fe2O3 Layer on the Photovoltaic Performance of Perovskite-Based Solar Cells. Journal of The Electrochemical Society. 165(2):30-38. https://doi.org/10.1149/2.1131802jesS3038165

Electrochemical Fabrication and Characterization of p-CuSCN/n-Fe2O3 Heterojunction Devices for Hydrogen Production

[EN] p-CuSCN/n-Fe2O3 heterojunctions were electrochemically prepared by sequentially depositing alpha-Fe2O3 and CuSCN films on FTO (SnO2:F) substrates. Both alpha-Fe2O3 and CuSCN films and alpha-Fe2O3/CuSCN heterojunctions were characterized by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Pure crystalline CuSCN films were electrochemically deposited on alpha-Fe2O3 films by fixing the SCN/Cu molar ratio in an electrolytic bath to 1:1.5 at 60 degrees C, and at a potential of -0.4 V. The photocurrent measurements showed increased intrinsic surface states or defects at the alpha-Fe2O3/CuSCN interface. The photoelectrochemical performance of the alpha-Fe2O3/CuSCN heterojunction was examined by chronoamperometry and linear sweep voltammetry techniques. The alpha-Fe2O3/CuSCN structure exhibited greater photoelectrochemical activity compared to the alpha-Fe2O3 thin films. The highest photocurrent density was obtained for the alpha-Fe2O3/CuSCN films in 1 M NaOH electrolyte. This strong photoactivity was attributed to both the large active surface area and the external applied bias, which favored the transfer and separation of the photogenerated charge carriers in the alpha-Fe2O3/CuSCN heterojunction devices. The flatband potential and donor density were maximal for the heterojunction. These results suggest a substantial potential to achieve heterojunction thin films in photoelectrochemical water splitting applications. (c) 2017 The Electrochemical Society. All rights reserved.This work was supported by the Ministry of High Education and Scientific Research (Tunisia), Ministerio de Economia y Competitividad (ENE2016-77798-C4-2-R) and Generalitat Valenciana (Prometeus 2014/044).Bouhjar, F.; Ullah, S.; Mollar García, MA.; Marí, B.; Bessais, B. (2017). Electrochemical Fabrication and Characterization of p-CuSCN/n-Fe2O3 Heterojunction Devices for Hydrogen Production. Journal of The Electrochemical Society. 164(13):936-945. https://doi.org/10.1149/2.1431713jes9369451641

Hydrothermal synthesis of nanostructured Cr-doped hematite with enhanced photoelectrochemical activity

[EN] Using the easily applicable hydrothermal method Cr-doped hematite thin films have been deposited polycrystalline on conductive glass substrates. The hydrothermal bath consisted of an aqueous solution containing a mixture of FeCl3.6H(2)O and NaNO3 at pH = 1.5. The samples were introduced in an autoclave and heated for a fixed time at a fixed temperature and then annealed in air at 550 degrees C. The concentration of the incorporated Cr atoms (Cr4+ ions) was controlled by varying the concentration of the Cr(ClO4)(3) precursor solution, varied from 0% to 20%. All samples followed morphological and structural studies using field-emission scanning electron microscopy, high-resolution transmission electron microscopy and X-ray diffraction. Chronoamperometry measurements showed that Cr-doped hematite films exhibited higher photoelectrochemical activity than the undoped films. The maximum photocurrent density and incident photon conversion efficiencies (IPCE) were obtained for 16 at.% Cr-doped films. This high photoactivity can be attributed to both the large active surface area and increased donor density caused by Cr-doping in the alpha-Fe2O3 films. All samples reached their best IPCE at 400 nm. IPCE values for 16 at.% Cr-doped hematite films were thirty times higher than that of undoped samples. This high photoelectrochemical performance of Cr-doped hematite films is mainly attributed to an improvement in charge carrier properties. (C) 2017 Elsevier Ltd. All rights reserved.This work was supported by the Ministry of Higher Education and Scientific Research, Tunisia and Ministerio de Economia y Competitividad (ENE2016-77798-C4-2-R) and Generalitat Valenciana (Prometeus 2014/044).Bouhjar, F.; Mollar García, MA.; Chourou, M.; Marí, B.; Bessais, B. (2018). Hydrothermal synthesis of nanostructured Cr-doped hematite with enhanced photoelectrochemical activity. Electrochimica Acta. 260:838-846. https://doi.org/10.1016/j.electacta.2017.12.049S83884626

Enhanced light trapping using plasmonic nanoparticles

International audiencePlasmonics is a new light trapping method used in photovoltaic (PV) solar cells. A significant enhancement of the scattered and absorbed incident light due to the use of silver nanoparticles (Ag-NPs) was observed, which yield to the exaltation of the electromagnetic field in the vicinity of these NPs. In this context, we investigate optically and morphologically the effect of the NPs size dependence on the localized surface plasmon resonance. Extinction, absorption and scattering cross sections are calculated using Mie theory

Electrodeposited chromium-doped alpha-Fe2O3 under various applied potential configurations for solar water splitting

[EN] In this work, high quality hematite (alpha-Fe2O3) Chromium (Cr)-doped thin films have been synthesized via electrodeposition technique, on fluorine-doped fin oxide-coated glass substrates, under various applied potential configurations [cyclic voltammetry (CV), linear sweep voltammetry (LSV) and - 0.5 V]. Chromium was added to the electrolyte at such a proportion that the Cr/(Cr + Fe) ratio remained within 8%. The as-deposited films were subsequently annealed in air at 650 degrees C for 2 h. Our novel study highlights the effect of using variable potential approaches during the film preparation on the properties of Cr-alpha-Fe2O3 deposited films. The prepared thin films were analyzed by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, UV-Vis absorption and photoelectrochemical (PEC) analysis. XRD revealed that samples are crystallized in Cr-Fe2O3 cubic structure with a crystalline orientation in the plane (1 1 1) and a clear improvement of the crystallinity and size crystallite of the Cr-Fe2O3 deposited using CV process. SEM micrographs showed that the morphology grains were three-sided pyramid-shaped, expanding with increase of the crystallinity. The calculated band gap values are 2.18, 2.23 and 2.20 eV, respectively for - 0.5 V, LSV, CV. The Cr-Fe2O3 films synthesized in this study showed high PEC activity with very low carrier density in comparison with the conventionally electrodeposited films. This Cr-doped hematite films 'excellent photoelectrochemical performance was mainly attributed to improved charge carrier properties. Such high photoactivity was attributed to the large active surface area and increased donor density caused by increasing the Cr doping in the alpha-Fe2O3 films.This work was supported by the Ministry of High Education and Scientific Research (Tunisia), the Ministry of Economy and Competitiveness (Spain) (ENE2016-77798-C4-2-R) and the Generalitat Valenciana (Prometeus 2014/044).Bouhjar, F.; Derbali, L.; Marí, B.; Bessais, B. (2020). Electrodeposited chromium-doped alpha-Fe2O3 under various applied potential configurations for solar water splitting. Results in Physics. 17:1-7. https://doi.org/10.1016/j.rinp.2020.102996S171

Electrodeposited Cr-Doped alpha-Fe2O3 thin films active for photoelectrochemical water splitting

[EN] Polycrystalline hematite (alpha-Fe2O3) Chromium (Cr)-doped thin films were electrodeposited on fluorine-doped tin oxide-coated glass substrates. The electrodeposition bath comprised an aqueous solution containing FeCl3 center dot 6H(2)O, NaCl, and H2O2.Chromium was added to the electrolyte at such a proportion that the Cr/(Cr + Fe) ratio remained within the 2-8 at. % range. The as-deposited films were subsequently annealed in air at 650 degrees C for 2 h. The structure and morphological characteristics of the undoped and Cr-doped alpha-Fe2O3 thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-Vis spectroscopy. Cr doping led the main XRD lines to shift to lower angles, which mostly resulted from substituting Fe3+ for Cr4+ ions that leads to alpha-Fe2O3 lattice contraction. The SEM observations showed that the roughness and aspect of surfaces changed with the Cr doping level. The photoelectrochemical (PEC) performance of the alpha-Fe2O3 films was examined by chronoamperometry and linear sweep voltammetry techniques. The Cr-doped films exhibited greater photoelectrochemical activity than the undoped alpha-Fe2O3 thin films. The highest photocurrent density was obtained for the 8% Cr-doped alpha-Fe2O3 films in 1 M NaOH electrolyte. All the samples achieved their best IPCE at 400 nm. The IPCE values for the 8 at.% Cr-doped hematite films were 20-fold higher than that of the undoped sample.This Cr-doped hematite films 'excellent photoelectrochemical performance was mainly attributed to improved charge carrier properties. Such high photoactivity was attributed to the large active surface area and increased donor density caused by increasing the Cr doping in the alpha-Fe2O3 films. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.This work was supported by the Ministry of High Education and Scientific Research (Tunisia), the Ministry of Economy and Competitiveness (Spain) (ENE2016-77798-C4-2-R) and the Generalitat Valenciana (Prometeus 2014/044).Bouhjar, F.; Derbali, L.; Marí, B.; Bessais, B. (2020). Electrodeposited Cr-Doped alpha-Fe2O3 thin films active for photoelectrochemical water splitting. International Journal of Hydrogen Energy. 45(20):11492-11501. https://doi.org/10.1016/j.ijhydene.2019.10.215S1149211501452

TiO

One of the most promising ideas to enhance the photocatalytic efficiency of the TiO2 is to couple this photocatalyst with other semiconductors. In this work, we report on the development of photo-catalytic properties of two types of composites based on TiO2 – ITO (Indium Tin Oxide) and TiO2 – ZnO deposited on conventional ceramic substrates. The samples were characterized by X-ray diffraction (XRD) and transmission Electron Microscopy (TEM). The photo-catalytic test was carried out under UV light in order to reduce/oxidize a typical textile dye (Cibacron Yellow). The experiment was carried out in a bench scale reactor using a solution having a known initial dye concentration. After optimization, we found that both nanocomposites exhibit better photocatalytic activity compared to the standard photocatalyst P25 TiO2

Local activation of light-induced degradation in co-doped boron-phosphorus silicon: Evidence of defect diffusion phenomena

International audienceThis study is interested in the local activation of Light-induced degradation (LID) defect in highly co-doped silicon wafers with boron and phosphorus. For this purpose, the experiments are focused on measuring the minority carrier lifetime before and after LID activation via a mapping technique. The LID defect density exhibits a Gaussian distribution centered on the excitation point of the laser beam; the intensity of the Gaussian distribution of the LID defect varies with the concentration of the co-dopants. The lifetime of the minority carriers decreases in all-silicon sample regions, while the excitation laser beam focuses on an area of approximately one mm2. This observation indicates that LID defects are activated even in the unexcited areas of silicon wafers, suggesting a LID diffusion phenomenon from the laser excitation point to the whole silicon wafer. We deduce that a high phosphorus doping level in silicon wafers leads to a significant reduction in the LID effect

Crystal growth and design of various shapes of PbS micro and nanocrystals from a hydrothermal process

[EN] This paper reports on a systematic study highlighting dramatic morphological changes during the preparation of Lead Sulfide (PbS) by a hydrothermal process. PbS micro/nanostructures having different shapes and sizes were prepared via a simple hydrothermal reaction between lead acetate and a sulfur precursor (Thiourea (Tu) or Na2S). We show that the shapes of the PbS micro/nanostructures can be tuned by varying the process parameters, for instance the concentration of the precursors (lead acetate and Thiourea), the reaction time and the reaction temperature. The hydrothermal ? based PbS structures were characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), High-Resolution TEM (HRTEM) and X-Ray Diffraction (XRD). We succeeded synthesizing PbS crystallites having symmetric six- and eight-arms starfish-shaped dendrites by using Thiourea (Tu) as anionic precursor. The decrease of Tu concentration as low as 0.05 M switches the crystal morphology to irregular flower- and cubic ? like shapes, while the increase of the reaction time up to 6 h leads to the formation of mono-arms dendrites. The addition of Triethylamine (TEA) to Tu in the initial reaction blocks the growth of the six-arm starfish shaped PbS crystals and leads to the formation of octahedral and sub-spherical crystals. A morphological change from starfish dendrites to crystalline nanoparticles occurs by replacing Tu by Na2S as a sulfur precursor; this transition from dendrites to nanoparticles was attributed to the nature of the anionic precursorThis work was supported by the University of Tunis El Manar (Tunisia) and Ministerio de Economia y Competitividad (Grant Number PID2019-107137RB-C21), SpainJemai, S.; Hajjaji, A.; Baig, F.; Harabi, I.; Marí, B.; Bessais, B. (2021). Crystal growth and design of various shapes of PbS micro and nanocrystals from a hydrothermal process. Materials Characterization. 175:1-8. https://doi.org/10.1016/j.matchar.2021.111036S1817

Photocatalytic indoor/outdoor air treatment and bacterial inactivation on CuxO/TiO2 prepared by HiPIMS on polyester cloth under low intensity visible light

International audienc