Abdelilah Slaoui

Optical and structural properties of Nd doped SnO2 powder fabricated by the sol–gel method

We report on the structural and optical properties of undoped and neodymium doped SnO2 powders (0, 1, 3, and 5 at% of Nd) synthesized by the sol–gel method. SEM and TEM microscopy techniques reveal a nanometric scale of the powders. We show that the tetragonal rutile phase is achieved after annealing at 700 °C. The crystallite size of the doped SnO2 is found to decrease gradually with the increase of Nd content without changing the SnO2 structure. A strong decrease in the intensity of the Raman peaks is noted for doped powders, which can be attributed to the location of Nd3+ ions at the Sn sites indicating Nd incorporation into the host matrix. For the first time the optical properties were studied by UV-Vis-NIR spectroscopy and revealed Nd related absorption bands in the SnO2 matrix. The investigation of the photoluminescence properties shows broad emission centred around 550–650 nm originating from defects present in the SnO2 host matrix. Under 325 nm laser excitation, a strong photoluminescence of trivalent Nd is observed in the infrared region and shows Nd related emission peaks at 885, 1065, and 1336 nm. Such a strong PL signal under laser excitation indicates that Nd3+ is optically active. The excitation dependent PL (PLE) recorded in the 450–700 nm range confirms the presence of active Nd3+ successfully inserted into the SnO2 host matrix.

Tuning the chemical properties of europium complexes as downshifting agents for copper indium gallium selenide solar cells

New europium(III) β-diketonate based complexes with the general formula [Eu(β-Dik)3(NL)x], where β-Dik = 2-thenoyltrifluoroacetonate, 4,4,4-trifluoro-1-phenyl-1,3-butanedione, 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione, NL = diphenyl sulfoxide (x = 2), bis[2-(diphenylphosphino)phenyl] ether oxide (x = 1), triphenylphosphine oxide (x = 2), 5,6-epoxy-5,6-dihydro-[1,10]phenanthroline (x = 1), are designed and synthesized. The coordination complexes are comprehensively characterized by elemental analysis, infrared and 1H, 13C and 19F NMR spectroscopy. The complexes are embedded into poly(ethylene-co-vinyl acetate) (EVA), poly(methyl methacrylate) (PMMA) or poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) (PVB) matrices. Photoluminescence behavior is investigated in detail and it exhibits the characteristic 5D0 → 7F0–4 emission bands with quantum yields of 55–83% in the solid state and 34–86% in the polymers. Encapsulation of CIGS solar cells with luminescent downshifting (LDS) layers results in an important improvement of external quantum efficiency (EQE) in the UV region, from 14% and up to 58% at 360 nm for the best compound. The short circuit current density (Jsc) in the range of 300–400 nm increases up to 0.77 mA cm−2 for the best LDS which corresponds to 71% of the Jsc enhancement of an ideal downshifter. I–V measurements follow the spectral response data with an absolute increase in conversion efficiency of up to 0.8%.

Insight into photon conversion of Nd3+ doped low temperature grown p and n type tin oxide thin films

The synthesis of multifunctional high-quality oxide thin films is a major current research challenge given their potential applications. Herein, we report on p and n type tin oxides thin films as functional TCOs with photon management properties through doping with Nd3+ rare earth ions. We show that the structure, composition, carrier transport and optical properties of the sputtered Nd:SnOx films can be easily tuned by simply varying the Ar/O2 gas flow ratio (R) during the deposition step. The increase of the oxygen content leads to drastic changes of the material properties from p-type SnO to n-type SnO2. Furthermore, all Nd:SnOx films are found to be highly conductive with resistivities as low as 1 × 10−3 Ω cm−1 and carrier mobilities up to 129 cm2 V−1 s−1. Thanks to deep XPS and NEXAFS spectroscopies, we gained insight into the coordination and oxidation degrees of the elements within the matrices. The insertion and optical activation of the incorporated Nd3+ ions have been successfully achieved in both matrices. As a consequence, strong NIR luminescence lines, typical of Nd3+ ions, were recorded under UV laser excitation. We experimentally show that the efficient Nd3+ photoluminescence in the near infrared region originates from efficient sensitization from the host matrix, through energy transfer. We found that the SnO2 host matrix provides more efficient sensitization of Nd3+ as compared to the SnO matrix. An energy transfer mechanism is proposed to explain the observed behaviour.

One step electrodeposited CZTS thin films: Preparation and characterization

Cu2ZnSnS4 (CZTS) thin films were successfully prepared using a single-step electrodeposition process in aqueous ionic solution, followed by the sulfurization in elemental sulfur vapor ambient at different annealing temperatures and under Argon atmosphere. The structural, morphological, compositional and optical properties of the samples have been investigated. Raman spectroscopy and X-ray diffraction (XRD) have confirmed the Kesterite structure of CZTS films sulfurized at 500 °C. The chemical composition was determined by Rutherford Back Scattering (RBS) and energy dispersive X-ray spectroscopy (EDS) that show the formation of near stoichiometric CZTS thin films. The surface morphology of the samples was examined using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Optical properties of the CZTS thin film were studied by photoluminescence spectroscopy (PL).

Absorption Enhancement in Thin-Film Solar Cells with Perforated Holes

A thin-film solar cell structure with an array of perforated air holes is modeled numerically. A systematic study is performed to demonstrate the effect of the lattice parameters and perforation depth on the short-circuit current density. The structure with optimal parameters exhibits a current density enhancement of 60.3%. The impact of the perforation on the decrease in the Fresnel reflection and increase in the absorption in the active layer by excitation of guiding modes in the structure is discussed.

Incorporation of dopant impurities into a silicon oxynitride matrix containing silicon nanocrystals

Dopant impurities, such as gallium (Ga), indium (In), and phosphorus (P), were incorporated into silicon-rich silicon oxynitride (SRSON) thin films by the ion implantation technique. To form silicon nanoparticles, the implanted layers were thermally annealed at temperatures up to 1100 °C for 60 min. This thermal treatment generates a phase separation of the silicon nanoparticles from the SRSON matrix in the presence of the dopant atoms. We report on the position of the dopant species within the host matrix and relative to the silicon nanoparticles, as well as on the effect of the dopants on the crystalline structure and the size of the Si nanoparticles. The energy-filtered transmission electron microscopy technique is thoroughly used to identify the chemical species. The distribution of the dopant elements within the SRSON compound is determined using Rutherford backscattering spectroscopy. Energy dispersive X-ray mapping coupled with spectral imaging of silicon plasmons was performed to spatially localiz...

Kesterite / wurtzite Cu 2 ZnSnS 4 nanocrystals: Synthesis and characterization for PV applications

Wet chemical synthesis and characterizations of quaternary chalcogenide Cu2ZnSnS4 (CZTS) nanocrystals, as an alternative solar absorber material to conventional quaternary CuInxGa(1−x)S2 (CIGS), is given in detailed. Dodecanethiol and oleylamine are used as hot organic solvents and capping ligands, as for oleic acid is used with dodecanethiol to control the nanocrystals morphology. Two kinds of metal precursors ae used: metal chlorides and metal acetate as precursors of Cu, Zn and Sn, respectively, while elemental sulfur is used as sulfur source. The effect of dodecanethiol and oleylamine on the final phase of the CZTS nanocrystals is studied. The as-synthesized (CZTS) nanocrystals are characterized by X-ray diffraction (XRD), Raman spectroscopy, and Transmission electron microscopy (TEM). Our results showed that CZTS nanocrystals can be obtained with different crystallographic phases, kesterite and wurtzite structures. Furthermore, we found that the CZTS nanocrystals structure can be controlled as kesterite phase or wurtzite phase using dodecanethiol-sulfur solution and oleic acid instead of oleylamine during the synthetic procedure.

Effect of ITO and Mo coated glass substrates on electrodeposited Cu 2 ZnSnS 4 thin films

Cu2ZnSnS4 (CZTS) thin films were elaborated at room temperature on ITO and Mo coated glass substrates using electrodeposition route, followed by a sulfurization treatment. We investigated the effect of the substrates on crystallographic structure, morphology, composition and optical properties of electrodeposited CZTS thin films. X-ray diffraction and Raman analysis showed that the deposited films were polycrystalline with kesterite structure. Film composition and surface morphology have been analyzed using Scanning electron microscopy and Energy dispersive analysis. Photoluminescence spectroscopy showed for both films a broad PL band centered around 1.5 eV.

Thickness effect on Cu 2 ZnSnS 4 properties using non-toxic and low-cost process

CZTS thin films were prepared by simple Sol-gel method. CZTS sol-gel mixture contains tin chloride, copper acetate, zinc acetate and thiourea as a source of sulfur. CZTS solution was then deposited on molybdenum coated glass substrates. The prepared thin films were annealed at 540 °C in sulfur atmosphere for one hour. CZTS films showed good crystalline quality and optical properties that depend on the film thickness. The measured films band gap was close to 1.43 eV with a good kesterite phase. The CZTS layer was used as an absorber in solar cell with the structure glass/Mo/CZTS/CdS/ZnO/AZO/Al and demonstrated an open circuit voltage of 66 mV and a short circuit current of 6.8 µA/cm2.

Study of sprayed CZTS thin films containing various copper content

By ultrasonic spray, we have deposited CZTS films on Mo coated substrates. A sulfurization treatment was systematically performed under Argon atmosphere at 500 °C for one hour. Copper content effect of CZTS thin films of about 1 µm was studied by X-ray diffraction, Raman spectroscopy and optical transmittance measurements. The films exhibited the kesterite structure despite the appearance of some secondary phases for a high and poor copper content. The gap energy value was sensitive to the copper content and ranged between 1.42 eV and 1.68 eV.