Influence of secondary phases during annealing on re-crystallization of CuInSe2 electrodeposited films

Electrodeposited CuInSe2 thin films are of potential importance, as light absorber material, in the next generation of photovoltaic cells as long as we can optimize their annealing process to obtain dense and highly crystalline films. The intent of this study was to gain a basic understanding of the key experimental parameters governing the structural–textural-composition evolution of thin films as function of the annealing temperature via X-ray diffraction, scanning/transmission electron microscopy and thermal analysis measurements. The crystallization of the electrodeposited CuInSe2 films, with the presence of Se and orthorhombic Cu2−xSe (o-Cu2−xSe) phases, occurs over two distinct temperature ranges, between 220 °C and 250 °C and beyond 520 °C. Such domains of temperature are consistent with the melting of elemental Se and the binary CuSe phase, respectively. The CuSe phase forming during annealing results from the reaction between the two secondary species o-Cu2−xSe and Se (o-Cu2−xSe+Se→2 CuSe) but can be decomposed into the cubic β-Cu2−xSe phase by slowing down the heating rate. Formation of liquid CuSe beyond 520°C seems to govern both the grain size of the films and the porosity of the substrate–CuInSe2 film interface. A simple model explaining the competitive interplay between the film crystallinity and the interface porosity is proposed, aiming at an improved protocol based on temperature range, which will enable to enhance the film crystalline nature while limiting the interface porosity

Raman microprobe characterization of electrodeposited S-rich CuIn(S,Se)2 for photovoltaic applications: Microstructural analysis

This article reports a detailed Raman scattering and microstructural characterization of S-rich CuIn(S,Se)2 absorbers produced by electrodeposition of nanocrystalline CuInSe2 precursors and subsequent reactive annealing under sulfurizing conditions. Surface and in-depth resolved Raman microprobe measurements have been correlated with the analysis of the layers by optical and scanning electron microscopy, x-ray diffraction, and in-depth Auger electron spectroscopy. This has allowed corroboration of the high crystalline quality of the sulfurized layers. The sulfurizing conditions used also lead to the formation of a relatively thick MoS2 intermediate layer between the absorber and the Mo back contact. The analysis of the absorbers has also allowed identification of the presence of In-rich secondary phases, which are likely related to the coexistence in the electrodeposited precursors of ordered vacancy compound domains with the main chalcopyrite phase, in spite of the Cu-rich conditions used in the growth. This points out the higher complexity of the electrodeposition and sulfurization processes in relation to those based in vacuum deposition techniques

Comportement électrochimique des interfaces Ta/Ta

Les propriétés de transfert électronique aux interfaces "M.I.E." (Métal/Isolant/Elec trolyte) ont été mises en évidence en s'appuyant sur l'exemple significatif du tantale. Ce métal, recouvert d'une couche passivante d'oxyde Ta2O5, a été étudié en présence du couple Fe (II)/Fe (III) en solution. Par ailleurs, le dépôt à l'interface d'un métal noble tel que le platine génère une structure "M.I.M." (Métal/Isolant/Métal) qui possède des propriétés de conduction remarquables. Le comportement électrochimique de cette "électrode modifiée" en présence d'un couple rédox en solution est très voisin de celui d'une électrode de platine pur

Analysis of S-rich CuIn(S,Se)2 layers for photovoltaic applications: Influence of the sulfurization temperature on the crystalline properties of electrodeposited and sulfurized CuInSe2 precursors

This paper reports the microstructural analysis of S-rich CuIn(S,Se)2 layers produced by electrodeposition of CuInSe2 precursors and annealing under sulfurizing conditions as a function of the temperature of sulfurization. The characterization of the layers by Raman scattering, scanning electron microscopy, Auger electron spectroscopy, and XRD techniques has allowed observation of the strong dependence of the crystalline quality of these layers on the sulfurization temperature: Higher sulfurization temperatures lead to films with improved crystallinity, larger average grain size, and lower density of structural defects. However, it also favors the formation of a thicker MoS2 interphase layer between the CuInS2 absorber layer and the Mo back contact. Decreasing the temperature of sulfurization leads to a significant decrease in the thickness of this intermediate layer and is also accompanied by significant changes in the composition of the interface region between the absorber and the MoS2 layer, which becomes Cu rich. The characterization of devices fabricated with these absorbers corroborates the significant impact of all these features on device parameters as the open circuit voltage and fill factor that determine the efficiency of the solar cells

Analyse des mécanismes de conversion photovoltaïque dans les cellules à base de Cu(In,Ga)(S,Se)2 électrodéposé (Projet CISEL)

National audienceThin film electrodeposited Cu(In,Ga)(S,Se) 2 solar cells with efficiencies of 11.4% have been demonstrated by the CISEL project, a record for this technology. We analyse the performance of these cells, with emphasis on identifying dominant photoconversion and loss mechanisms. The current voltage characteristics of samples with a range of structures are analysed over a range of temperatures to provide understanding of mechanisms. Further identical samples with varying efficiencies are analysed in order to pinpoint loss mechanisms and means of improving the cells. We find that photocurrent losses dominate, whereas dark current parameters are less responsible for efficiency variations observed. This is confirmed by studies of the crystallinity of the devices

Cu(In,Ga)(S,Se)2 solar cells and modules by electrodeposition

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