Synthesis of in-gap band CuGaS2:Cr absorbers and numerical assessment of their performance in solar cells

[EN] CuGaS2 thin films were obtained by sulfurization of CuGaSe2. CuGaSe2 thin films were first electrodeposited from aqueous solutions containing CuCl2, GaCl3, and H2SeO3 and subsequently annealed at 400 °C for 10 min in forming gas atmosphere and in the presence of molecular sulfur. This sulfurization process resulted in the complete conversion of CuGaSe2 into CuGaS2. The formation of CuGaS2 was proven by X-Ray diffraction and optical spectroscopy. Diffraction peaks of CuGaS2 shifted to higher angles than those observed for CuGaSe2 films, and the optical band gap shifted to blue rising from 1.66 eV for CuGaSe2 to 2.2 eV for CuGaS2. When Cr ions were added to the initial electrolyte, the final CuGaS2 films exhibited a broad in-gap absorption band centred at 1.63 eV that can be ascribed to Cr atoms in Ga sites. The performance of solar cells based on CuGaS2:Cr absorbers containing an in-gap absorption band was then estimated by numerical simulation using Solar Cell Capacitance Simulator Software. Both quantum efficiency and short circuit current of simulated Mo/CuGaS2:Cr/CdS/ZnO solar cells rose up proportionally to the amount of Cr present in CuGaS2:Cr absorbers. As a result, the photo conversion efficiency of the simulated devices changed from 14.7% for CuGaS2 to 34% for CuGaS2:Cr absorbers. Nevertheless, when neutral defects related to Cr-doping were introduced in the absorber layer, the positive effect of the enhancement of photon harvesting due to IGB was compensated by a decline in the carrier collection and the overall efficiency of the device fell considerably.This work was supported by Ministerio de Economia y Competitividad (ENE2016-77798-C4-2-R) and Generalitat Valenciana (Prometeus 2014/044).Ullah, S.; Ullah, H.; Bouhjar, F.; Mollar García, MA.; Marí, B. (2018). Synthesis of in-gap band CuGaS2:Cr absorbers and numerical assessment of their performance in solar cells. Solar Energy Materials and Solar Cells. 180:322-327. https://doi.org/10.1016/j.solmat.2017.06.062S32232718

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

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

Single Step Electrodeposited Kesterite Cu2ZnSnS4 (CZTS) thin films at low annealing temperatures

[EN] This paper reports onthe growth of quaternary Cu2ZnSnS4 (CZTS) thin films by a single step electrochemicaldeposition followed by annealing at low temperature.The influence of different annealing atmospheres at constant annealingtimes (t = 45min) and fixed preparation controlling parameters; i.e., starting materials (precursor metal salts) solution concentration, time of deposition and electrodeposition potential. Structural, compositional, morphological, andoptical properties, as well as photoelectrochemical properties were studied. The films, sulfurized during 2 hours, showeda prominent kesterite phase with a nearly stoichiometric composition. Samples were characterizedby X-ray diffraction (XRD), scanning electron microscopy (SEM), EDS and UV-VIS-NIR spectrometry. X-ray diffraction and confirmed the formation of pure kesterite CZTS films. SEM shows that films are compact with densemorphology and homogeneous distribution. EDS analyzed the elemental constituents of the quaternary Cu2ZnSnS4 with an apparent Cu deficiency and S rich for the sulfurized samples. From optical study, the energy gap was indexed for the sulfurized samples,Eg=1.52 eV. Under illumination sulfurized CZTS films exhibits negative photocurrent and positive photovoltagevalues confirming the p-type character of the films.This work was supported by the Culture, Affairs and Missions Sector, Ministry of Higher Education and Scientific Research (Egypt) and Ministerio de Economia y Competitividad (Spain) (ENE2016-77798-C4-2-R) and Generalitat valenciana (Prometeus 2014/044).Marí, B.; Mollar García, MA.; El Nahrawy, A.; Saber, S.; Khattab, N.; Eid, A.; Abo-Aly, M.... (2018). Single Step Electrodeposited Kesterite Cu2ZnSnS4 (CZTS) thin films at low annealing temperatures. Insights in Analytical Electrochemistry. 4(1:8):1-6. https://doi.org/10.21767/2470-9867.100028S1641:

Preparation et performance d'une cellule photocatalytique à base d'hématite pour la génération d'hydrogène

Tesis por compendioEl hidrógeno es un portador de energía que ya ha demostrado su capacidad para reemplazar el petróleo como combustible. Sin embargo, los medios de producción actualmente en uso siguen siendo altamente emisores de gases de efecto invernadero. La foto-electrólisis del agua es un proceso que, a partir de la energía solar, separa los compuestos elementales del agua como el hidrógeno y el oxígeno utilizando un semiconductor con propiedades físicas adecuadas. La hematita (¿-Fe2O3) es un material prometedor para esta aplicación debido a su estabilidad química y su capacidad para absorber una porción significativa de la luz (con una banda prohibida entre 2.0 - 2.2 eV). A pesar de estas propiedades ventajosas, existen limitaciones intrínsecas al uso de óxido de hierro para la descomposición fotoelectroquímica del agua. La primera restricción es la posición de su banda de conducción que es menor que el potencial de reducción de agua. Esta limitación se puede superar mediante la adición en serie de un segundo material, en tándem, que absorberá una parte complementaria del espectro solar y llevar a los electrones a un nivel de energía más alto que el potencial para la liberación de hidrógeno. El segundo obstáculo proviene del desacuerdo entre la corta longitud de difusión de los portadores de carga y la profundidad de penetración larga de la luz. Por lo tanto, es necesario controlar la morfología de los electrodos de hematita en una escala de tamaño similar a la longitud de transporte del orificio. En esta tesis, se introduce un nuevo concepto para mejorar el rendimiento fotoelectroquímico de la hematita. Usando el método hidrotermal depositamos capas delgadas de hematita dopada con Cr en sustratos de vidrio conductivo. También se ha preparado por medios electroquímicos una heterounión del tipo p-CuSCN/n-Fe2O3 depositando secuencialmente una capa de ¿-Fe2O3 y una película de CuSCNsobre sustratos de FTO (SnO2: F).Finalmente, se ha preparado células solares de perovskitas y óxido de hierro. Para ello se depositó una capa delgada, densa y uniformede óxido de hierro (¿-Fe2O3) como capa de transporte de electrones (ETL) en lugar de dióxido de titanio (TiO2) que se utiliza convencionalmente en las células fotovoltaicas perovskitastipoCH3NH3PbI3 (SGP). Este último dispositivo mostró un aumento en la fotocorriente del 20% y un IPCE30 veces mayor que la hematita simple, lo que sugiere una mejor conversión de las longitudes de onda por encima de 500 nm. Palabras clave: Fotoelectroquímica, división de agua, producción de hidrógeno, evolución de oxígeno, semiconductores de óxido de metal, hematita, óxido de hierro, nanoestructurasHydrogen is an energy carrier that has already demonstrated its ability to replace oil as a fuel. However, the means of production currently used remain highly emitting greenhouse gases. Photo-electrolysis of water is a process that uses solar energy to separate the elemental compounds of water such as hydrogen and oxygen using a semiconductor with adequate physical properties. Hematite (¿-Fe2O3) is a promising material for this application because of its chemical stability and ability to absorb a significant portion of light (with a band-gap between 2.0 - 2.2 eV). Despite these advantageous properties, there are intrinsic limitations to the use of iron oxide for the photoelectrochemical cracking of water. The first constraint is the position of its conduction band, which is lower than the water reduction potential. This constraint can be overcome by the addition in series of a second material, in tandem, which will absorb a complementary part of the solar spectrum and bring the electrons to a higher energy level than the potential of hydrogen release. The second obstacle comes from the disagreement between the short diffusion length of the charge carriers and the long light penetration depth. It is therefore necessary to control the morphology of the hematite electrodes on a scale of similar size to the transport length of the hole. In this thesis a new concept is introduced to improve the photoelectrochemical performances. Using the hydrothermal method we deposited thin layers of Cr-doped hematite on conductive glass substrates. We also electrochemically prepared a p-CuSCN / n-Fe2O3 heterojunction by sequentially depositing ¿-Fe2O3 and CuSCN films on FTO (SnO2: F) substrates. Finally, we have used uniform and dense thin layers of iron oxide (¿-Fe2O3) as an electron transport layer (ETL) in place of titanium dioxide (TiO2) conventionally used in photovoltaic cells based on perovskites CH3NH3PbI3 (PSC). This latter concept showed a 20% increase of the photocurrent and an IPCE 30 times greater than the simple hematite, suggesting better conversion of high wavelengths (> 500 nm). Keywords: Photoelectrochemistry, Water Splitting, Hydrogen Production, Oxygen Evolution, MetalOxide Semiconductors, Hematite, Iron Oxide, Nanostructures, Surface.L'hidrogen és un proveïdor d'energia que ja ha demostrat la seva capacitat per reemplaçar el petroli com a combustible, però els mitjans de producció actuals continuen essent fortament emissors dels gasos responsables d'efecte hivernacle. La fotoelectròlisi de l'aigua és un procés que, a partir de l'energia solar, separa els compostos elementals d'aigua com l'hidrogen i l'oxigen utilitzant un semiconductor amb propietats físiques adequades. La hematita (¿-Fe2O3) és un material prometedor per a aquesta aplicació a causa de la seva estabilitat química i capacitat d'absorbir una porció significativa de la llum (amb un gap entre 2,0 i 2,2 eV). Malgrat aquestes propietats avantatjoses, hi ha limitacions intrínseques per a l'ús d'òxid de ferro per a la descomposició fotoelectroquímica de l'aigua. La primera restricció és la posició de la seva banda de conducció que és inferior al potencial de reducció d'aigua. Aquesta limitació es pot superar mitjançant l'addició en sèrie d'un segon material, en tàndem, que absorbirà una part complementària de l'espectre solar i portar els electrons a un nivell d'energia més alt que el potencial per a l'alliberament d'hidrogen. El segon obstacle prové del desacord entre la curta durada de la difusió dels portadors de càrrega i la llarga profunditat de penetració de la llum. Per tant, és necessari controlar la morfologia dels elèctrodes d'hematita en una escala de mida similar a la longitud del forat del transport. En aquesta tesi, es presenta un nou concepte per millorar el rendiment fotoelectroquímic. Mitjançant el mètode hidrotermal es van dipositar capes primes de hematita Cr-doped sobre substrats de vidre conductor. També s'han preparat electroquímicamentheterounions de tipus p-CuSCN/n-Fe2O3 dipositant seqüencialment una capa de ¿-Fe2O3 i altra de CuSCN sobre substrats FTO (SnO2: F).Finalment, s'han produït cél·lules solars de perovskitesi óxid de ferro. Per això es va depositaruna capa prima,densai uniforme d'òxid de ferro (¿-Fe2O3) com a capa de transport d'electrons (ETL) en lloc de diòxid de titani (TiO2) que s'utilitza convencionalment en les cèl·lules fotovoltaiques de perovskita híbrida del tipus CH3NH3PbI3 (SGP). Aquest últim dispositiu va mostrar un augment del fotocorrent del 20% i una IPCE30 vegades superior a la hematita simple, la qual cosa suggereix una millor conversió a longitud d'ones per sobre de 500 nm. Paraules clau:Fotoelectroquímica, divisió d'aigua, producció d'hidrogen, evolució d'oxigen, semiconductors d'òxids metàl·lics, hematita, òxid de ferro, nanoestructures.Bouhjar, F. (2018). Preparation et performance d'une cellule photocatalytique à base d'hématite pour la génération d'hydrogène [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/106345TESISCompendi

Low-cost kesterite (CZTS) bilayers as an effective hole-transport layer for perovskite solar cells

[EN] This study investigates the utility of Copper Zinc Tin Sulfide (CZTS) thin films as inorganic hole-transporting layers (HTLs) in low-temperature perovskite solar cells (PSCs). The primary goal is to improve power conversion efficiencies (PCE) in PSCs using CZTS thin films fabricated through solution-based methods, with CH3NH3PbI3 perovskite and ZnO serving as the light-absorbing and electron-transporting components, respectively. Precise control over CZTS thin film growth significantly influences the formation of uniform perovskite layers. The study underscores the importance of achieving dense ZnO films with suitable grain sizes to confirm consistent coverage of perovskite films, enabling efficient charge transport while reducing recombination at the CZTS/perovskite interface. Results reveal that CZTS/CZTS bilayers exhibit superior photoelectrochemical performance compared to conventional CZTS (A)/FTO and CZTS (B)/CZTS (A) configurations. Evaluation of water splitting performance demonstrates that the CZTS/CZTS bilayer photoelectrode achieves the maximum photocurrent density, reaching 12 mA/cm2 vs. Ag/AgCl, with an Incident Photon-to-Current Efficiency of 9 % at 400 nm and an applied potential of 0.4V vs. Ag/AgCl. The study comprehensively examines CZTS impact on PSC photovoltaic properties and stability, culminating in a high-performance device with a PCE potential of up to 7 %. This underscores the pivotal role of CZTS- perovskite contacts in determining PSC photovoltaic performance and highlights CZTS potential as a versatile HTM for various PSCs designs.The author extend their appreciation to the deanship of scientific research at Shaqra University for funding this research work through the project number (SU-ANN-202252).Bouhjar, F.; Derbali, L.; Khattak, YH.; Marí, B. (2024). Low-cost kesterite (CZTS) bilayers as an effective hole-transport layer for perovskite solar cells. Optical Materials. 147. https://doi.org/10.1016/j.optmat.2023.11458214

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

The influence of a dielectric spacer layer on the morphological, optical and electrical properties of self-dewetted silver nanoparticles

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