M. Abd-Lefdil

Temperature growth and annealing effects on CdS thin films prepared by chemical bath deposition process

Homogeneous and strongly adherent CdS very thin films of about 70 nm are elaborated by the chemical bath deposition process. Structural, morphological, optical and electrical properties of the obtained layers are studied for different bath temperatures and after thermal annealing. An important change in the preferred orientation of CdS structure, from (002) to (101), with temperature growth and annealing treatment is reported. The films were resistive and highly transparent with an energy gap value of about 2.37 eV.

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).

Structural, Optical and Electrical Properties of ZnO Sprayed Thin Films Doped with Fluorine

F-doped ZnO films (FZO) of about 400 nm thicknesses were prepared on glass substrates by the chemical spray pyrolysis technique. X-ray diffraction patterns showed that the undoped and F-doped ZnO films exhibit the hexagonal wurtzite crystal structure with a preferential orientation along [002] direction. No secondary phase is observed in F-doped ZnO films. All films exhibit a transmittance around 80% in the visible range. Photoluminescence spectra at room temperature of undoped and F doped ZnO thin films are presented. The wide PL bands centered at 510 and 680 nm are characteristic of deep levels of oxygen vacancies in the ZnO matrix, and zinc interstitial position. The FZO films are degenerate and exhibit n-type electrical conductivity. The lowest electrical resistivity was 7.6 10−3 Ω cm.

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.

Pulsed laser deposition of CZTS thin films, their thermal annealing and integration into n-Si/CZTS photovoltaic devices

The pulsed laser deposition (PLD) technique is used for the room-temperature (RT) deposition of Cu2ZnSnS4 (CZTS) films. The PLD-CZTS films were subjected to post-annealing at different temperature ranging from 300–500°C in argon atmosphere. The X-ray diffraction and Raman analyses confirmed that the films crystallize in the kesterite structure regardless of their annealing temperature (Ta), but their crystallite size is found to increase with Ta and reaches its maximum value of 37 nm for Ta=400°C. The corresponding optical bandgap value of the PLD-CZTS films post-annealed at 400°C was found to be 1.6 eV. These PLD-CZTS films were directly integrated into Al/n-Si/PLD-CZTS/Al heterojunction PV devices without resorting to any surface treatment and/or post-sulfurization process. Under standard AM1.5 solar illumination, the Al/n-Si/PLD-CZTS/Al PV devices were found to yield a power conversion efficiency (η) of 1.1%, with a Voc of 0.140 V, a Jsc of 26 mA/cm2 and a fill factor of 31%. Even if the obtained η value is still modest, it underlines nonetheless the promising potential of PLD-CZTS films as an effective absorber layer in Si-based heterojunction solar cells.

Optical, structural and Photoconductivity properties of organic photovoltaic thin films based on polymer/fullerene

Morphological properties of two p-type semiconductors, used separately with fullerene: MEH-PPV and the commonly used P3HT, are investigated in order to study their influence on optical and Photoconductivity properties of organic thin films based on MEH-PPV/P3HT, separately, with and without PCBM. The aim is to better understand the charge carriers mechanisms inside the polymers and the effect of PCBM when added in blend. To measure morphologic and optical properties of the prepared thin films, different characterizations are performed. A comparative study of both polymers is discussed using X ray diffraction, absorption, photolumenescence and Raman spectra.

Nanoscale probing of optical and structural properties of polymeric photovoltaic thin films

Herein, we performed a comparative study of bulk heterojunction, bilayer architectures of thin films based MEH-PPV and PCBM dissolved in chlorobenzene. This study aims to investigate the impact of deposition of successive layers on optical characteristics of the active layer. The films were examined using UV-absorption, Photoluminescence X-ray diffraction and Scanning electron microscopy SEM.

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.