Préparation et étude de couches minces de CuXY2_2 (X = Ga, In ; Y = Se, Te) pour applications en cellules solaires

This paper concerns the study of thin films of CuXY$_2$ (X = Ga, In; Y = Se, Te) photovoltaic materials. The thin films were grown from a close-spaced vapour transport technique in closed tube, with iodine as reagent. After a review of the method and the published results concerning the thermodynamical aspect, we give some results of characterization of the thin films grown with this method. The conditions of quasi-stoichiometric deposition were determined. Phase transitions were observed: for example, for CuInSe$_2$ and at source temperatures above 580°C, the films are formed of (In, Se) compounds, mainly In$_2$Se$_3$ and InSe. These films have a n-type conductivity, while the CuInSe$_2$ films, obtained at $T < 580~^\circ$C, have a p-type conductivity. Hence, either p-type or n-type films can be grown, simply by varying the source temperature. These results were complemented by a study of the films grown by close-spaced sublimation (CSS) at moderate temperature, using the same apparatus. The films are also formed of (In, Se) compounds.Cet article concerne l'étude de couches minces de matériaux photovoltaïques CuXY$_2$ (X = Ga, In ; Y = Se, Te) obtenues par une méthode de transport chimique à courte distance (CSVT) en tube fermé, en présence d'iode. Après un rappel de la méthode, et une synthèse des résultats déjà publiés sur l'aspect thermodynamique, nous donnons des résultats de caractérisation des couches minces obtenues. Les conditions de dépôt quasi-stœchiométriques ont été déterminées. Des transitions de phase ont été trouvées : par exemple, pour CuInSe$_2$ et pour des températures de source $>580~^\circ$C, les couches sont formées de composés (In, Se), en particulier In$_2$Se$_3$ et InSe. Ces couches sont de type n, alors que les couches de CuInSe$_2$, obtenues pour $T < 580~^\circ$C, sont de type p. On peut donc déposer successivement des couches p et n simplement en variant la température. Ces résultats ont été complétés par une étude des couches obtenues par sublimation à courte distance (CSS) à température modérée, en utilisant le même appareillage. On retrouve des couches formées de composés (In, Se)

Modeling and experimental investigation of the close-spaced vapor transport process for the growth of CuIn(S 0,4 Se 0,6 ) 2 thin films

International audienceThis paper reports the prediction of optimal conditions to grow good quality crystalline thin films using the Close-Spaced Vapor Transport process. A new configuration of the horizontal reactor is used and presented. A thermodynamic model is proposed for the Cu-In-S-Se-I system to describe the deposition of CuIn(S0,4Se0,6)2(CISS) compound. The simulation was performed using the SOLGASMIX software which gives the composition of the chemical system at the thermodynamic equilibrium. The model is based on the minimization of the Gibbs energy of the defined chemical system. The present study has allowed us to determine the influence of the source temperature (TS) and iodine pressure (PI2) on the growth of CISS thin films. The different compounds of the solid phase were predicted for various TS and PI2 values. The conditions of stoichiometric and quasi-stoichiometric deposition are 475 ≤ TS ≤ 525 °C and PI2 ≤ 3 kPa. Some deduced conditions from the theoretical prediction were tested experimentally. The CISS samples grown have been analyzed by X-ray diffraction and scanning electron microscope. The thin films, deposited in optimal conditions, are stoichiometric

Modeling and experimental investigation of the close-spaced vapor transport process for the growth of CuIn(S 0,4 Se 0,6 ) 2 thin films

International audienceThis paper reports the prediction of optimal conditions to grow good quality crystalline thin films using the Close-Spaced Vapor Transport process. A new configuration of the horizontal reactor is used and presented. A thermodynamic model is proposed for the Cu-In-S-Se-I system to describe the deposition of CuIn(S0,4Se0,6)2(CISS) compound. The simulation was performed using the SOLGASMIX software which gives the composition of the chemical system at the thermodynamic equilibrium. The model is based on the minimization of the Gibbs energy of the defined chemical system. The present study has allowed us to determine the influence of the source temperature (TS) and iodine pressure (PI2) on the growth of CISS thin films. The different compounds of the solid phase were predicted for various TS and PI2 values. The conditions of stoichiometric and quasi-stoichiometric deposition are 475 ≤ TS ≤ 525 °C and PI2 ≤ 3 kPa. Some deduced conditions from the theoretical prediction were tested experimentally. The CISS samples grown have been analyzed by X-ray diffraction and scanning electron microscope. The thin films, deposited in optimal conditions, are stoichiometric

Analysis of electrical conduction mechanism in the high temperature range of the nanostructured photoabsorber Cu 2 SnS 3

International audienceThe dynamic electrical conduction in the bulk ternary semiconductor compound Cu2SnS3 is studied for the first time in the high temperature range from 300 °C to 440 °C in the frequency range 1 kHz–1 MHz. New activation energy for conduction mechanism is obtained and its frequency dependence is analyzed. The Cole–Cole representation is almost half circular indicating a single contribution to total electrical conduction through the material. The activation energy for the mean relaxation process, obtained separately from the analysis of imaginary part Z″ of complex impedance Z* and from the equivalent electric circuit, is estimated to be (942 +74). The correlated barrier hopping model is considered to analyze the experimental data. The results are compared with those obtained previously in low temperature range

The effect of thickness on the physico-chemical properties of nanostructured ZnO:Al TCO thin films deposited on flexible PEN substrates by RF-magnetron sputtering from a nanopowder target

International audienceNanostructured aluminum-doped ZnO (ZnO:Al) thin films of various thicknesses were deposited on flexible Poly-Ethylene Naphthalate (PEN) substrates by RF-magnetron sputtering without intentionally heating them to fabricate Transparent Conductive Oxides (TCOs). The compacted ZnO:Al nanopowder with an [Al]/[Zn] ratio of 2%, which was synthesized by the sol-gel method combined with a supercritical drying process, was used as target in the sputtering system. The structural, morphological, optical and electrical properties of the deposited thin films of various thicknesses have been investigated. X-ray diffraction results indicate that all of the deposited thin films have a hexagonal wurtzite structure with c-axis orientation without any secondary phases. The Scanning Electron Microscopy (SEM) cross section images revealed that the films have a dense columnar nanostructure. The atomic percentage of the compositional elements in the films was nearly the same as that in the sputtering nanopowder target. Below a critical thickness of 500 nm, the films exhibit a high transmittance (>77% including the contribution of the PEN substrate) in the visible region. However, the electrical resistivity, Hall mobility and carrier concentration were significantly affected with the increase of film thickness. For thicknesses higher than 500 nm, the thin films exhibit similar electrical properties (resistivity of 3.5×10−4 Ω cm and Hall mobility of 22 cm2 V−1 s−1) but the transmittance decreases in the visible region. The Photoluminescence spectra showed that the Zn interstitial atoms, which enhance the conductivity of the films, are more dominant than the other defects

Effect of sputtering power on the electrical and optical properties of Ca-doped ZnO thin films sputtered from nanopowders compacted target

International audienceIn the present work, we have deposited calcium doped zinc oxide thin films by magnetron sputtering technique using nanocrystalline particles elaborated by sol–gel method as a target material. In the first step, the nanoparticles were synthesized by sol–gel method using supercritical drying in ethyl alcohol. The structural properties studied by X-ray diffractometry indicates that Ca doped ZnO has a polycrystalline hexagonal wurzite structure with a grain size of about 30 nm. Transmission electron microscopy (TEM) measurements have shown that the synthesized CZO is a nanosized powder. Then, thin films were deposited onto glass substrates by rf-magnetron sputtering at ambient temperature. The influence of RF sputtering power on structural, morphological, electrical, and optical properties were investigated. It has been found that all the films deposited were polycrystalline with a hexagonal wurtzite structure and preferentially oriented in the (0 0 2) crystallographic direction. They have a typical columnar structure and a very smooth surface. The as-deposited films show a high transmittance in the visible range over 85% and low electrical resistivity at room temperature

Influence of sputtering power on the properties of thin layers of GZO for photovoltaic applications

International audienceIn the present work, we have deposited gallium doped zinc oxide thin films by magnetron sputtering technique based nanocrystalline particles elaborated by sol–gel method. In the first step, the nanoparticles were synthesized by sol–gel method using supercritical drying in ethyl alcohol. The structural studied by X-ray diffractometry indicates that GZO has a polycrystalline hexagonal wurzite structure with a grain size of about 30 nm. Transmission electron microscopy measurements have shown that very small particles of GZO are present in the aerogel powder. Then, thin films were deposited onto glass substrates by rf-magnetron sputtering at ambient temperature. The influence of RF sputtering power on structural, morphological, electrical, and optical properties were investigated. It has been found that all of the films deposited were polycrystalline with a hexagonal wurtzite structure and preferentially oriented in the (002) crystallographic direction. The film deposited at 60 W showed the lowest electrical resistivity of 3.5 × 10−3 Ω cm achieved through the highest Hall mobility of 9.30 cm2 V−1 s−1. All the GZO films in this study showed the optical transmittances higher than 80 %

Analysis of electrical conduction mechanism in the high temperature range of the nanostructured photoabsorber Cu 2 SnS 3

International audienceThe dynamic electrical conduction in the bulk ternary semiconductor compound Cu2SnS3 is studied for the first time in the high temperature range from 300 °C to 440 °C in the frequency range 1 kHz–1 MHz. New activation energy for conduction mechanism is obtained and its frequency dependence is analyzed. The Cole–Cole representation is almost half circular indicating a single contribution to total electrical conduction through the material. The activation energy for the mean relaxation process, obtained separately from the analysis of imaginary part Z″ of complex impedance Z* and from the equivalent electric circuit, is estimated to be (942 +74). The correlated barrier hopping model is considered to analyze the experimental data. The results are compared with those obtained previously in low temperature range

Sputtered Al-doped ZnO transparent conducting thin films suitable for silicon solar cells

International audienceHighly transparent conducting Al-doped zinc oxide (AZO) thin films have been grown onto p-type porous silicon substrates by RF-magnetron sputtering at room temperature using aluminum doped nanocrystalline powder. The obtained AZO films were polycrystalline with a hexagonal wurtzite structure and preferentially oriented in the (002) crystallographic direction. The films are highly transparent in the visible wavelength region with a transmittance higher than 85% and an electrical resistivity of 1.56 × 10− 4 Ω·cm was obtained at room temperature. On the other hand, we have studied the position of the p–n junction involved in the In2O3:SnO2/(n)AZO/Si(p) structure, by electron-beam induced current technique. Current density–voltage characterizations in dark and under illumination were also investigated. The cell exhibits an efficiency of 5%

Characteristics of nanostructured Zn1-xVxO thin films with high vanadium content elaborated by rf-magnetron sputtering

Nanostructured Zn1−xVxO (0 ⩽ x ⩽ 0.50) thin films were synthesized by rf-magnetron sputtering at two different substrate temperatures (room temperature (RT) and 200 °C) and with variable sputtering powers (60, 80 and 100 W). In this method, single targets based on Zn1−xVxO nanopowders prepared by the sol–gel process were used. Characterization of the Zn1−xVxO nanoparticles showed that they crystallize in the hexagonal wurtzite structure. Their size ranged from 20 to 40 nm. The effect of process parameters on the physical and chemical properties of Zn1−xVxO thin films has been studied. For x ⩽ 0.30, the results obtained at 200 °C and 60 W indicate that the films have a high quality of crystallinity. Vegard’s law is respected, indicating that vanadium is incorporated in the ZnO matrix. The chemical compositions of these films were found to be close to the stoichiometry. The films exhibit a columnar structure and a smooth surface. Their average transmission, from the visible to the NIR, was in the range of 75–90%. The values of the band gap of the Zn1−xVxO thin films with x ⩽ 0.30 and elaborated at 200 °C and 60 W, vary from 3.29 to 3.74 eV. This is consistent with blue shifting of near-band edge cathodoluminescence emission. Under particular growth conditions, the investigation shows that the Zn0.80V0.20O sample presents the best properties for potential use in various optoelectronic applications, namely: a single wurtzite phase, low surface roughness (Ra ∼ 0.2 nm), a high transparency of 90% in the UV–Vis–NIR, a wide band gap of 3.74 eV and a resistivity of ∼5 × 10+3 Ω cm