Pierre-Philippe Grand

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. ...

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 bec...

First Stages of CuInSe2 Electrodeposition from Cu(II)-In(III)-Se(IV) Acidic Solutions on Polycrystalline Mo Films

The first stages of the electrochemical deposition of a Cu-In-Se compound on molybdenum-coated glass were investigated. The surface morphology was examined after various deposition times by a field emission gun-scanning electron microscope. The surface composition and chemical environment analysis were characterized by X-ray photoelectron spectroscopy (XPS). Raman spectroscopy, X-ray diffraction, and X-ray fluorescence were also performed. This enabled the growth steps to be evidenced. A quasi-instantaneous three-dimensional nucleation occurs. The first nuclei are made of a copper-rich Cu-Se phase without indium. Codeposition of indium starts when the Se/Cu surface ratio reaches a value close to 1, which confirms that the formation of a Cu-Se phase is a prerequisite for indium incorporation. With increasing the deposition time, the In/Cu surface ratio increases and tends to a constant value close to 0.5, smaller than the bulk value. The Se/Cu ratio increases first rapidly and then more slowly, when coalescence of the nuclei has occurred. XPS analysis shows that this two-step behavior corresponds to an evolution of the chemical environment of the Se species, indicating the presence of several Se compounds in the film. X-ray diffraction and Raman spectroscopy confirm the presence of a Cu-Se phase and elemental Se, in addition to the predominant chalcopyrite phase.

Electrodeposition of Indium on Copper for CIS and CIGS Solar Cell Applications

The electrodeposition of indium on copper substrates is studied in an acid sulfate solution for applications in CuInS 2 (CIS) and Cu(InGa)Se 2 (CIGS) solar cells. The study is focused on the film morphology and thickness uniformity on the nanometer scale. A two-step film growth behavior was observed, a conformal smooth film growth followed by a three-dimensional island growth. A hypothesis involving the Cu-In alloy formation and the Cu-In interdiffusion is proposed. While the room temperature alloy formation promotes the conformal deposition of a few monolayers of alloy, the fast interdiffusion between Cu and In further extends this alloy formation to a thicker layer and delays the typical island formation-growth phenomenon.

Copper indium diselenide solar cells prepared by electrodeposition

Copper indium diselenide (CIS) layers have been prepared by an electrodeposition based process. The composition, density and adhesion properties of theses films were found to be highly suitable for use as the active layer in a CIS solar cell. After recrystallisation and the completion of the device layer (by the deposition of CdS and ZnO layers), efficiencies as high as 8.8 % were found (total area, 100 MW/cm/sup 2/, no AR coating) for small area devices (0.06 cm/sup 2/). To the best of our knowledge, this is a record efficiency for electrodeposited CIS, without any post additional vacuum deposition process. Promising results have been also obtained on 5/spl times/5 cm/sup 2/ substrates (average efficiency of 4.5 %).

Solution Processing Route to High Efficiency CuIn(S,Se)2 Solar Cells

Inorganic semiconductors have properties that are notoriously difficult to control due to the deleterious impact of crystalline imperfections, and this is especially so in solar cells. In this work, it is demonstrated that materials grown using wet chemistry processes for the preparation of nanocristalline precursors can achieve the same performance as the best state of the art, namely conversion efficiencies above 11% with CuInS2. Interestingly, due to the growth process, the active material inherit a porous morphology that is shown to play a part in the performance and functionality of the active material. The new device morphology leads to a device operation closer to that of nanoscale organic interpenetrated solar cells or dye sensitized solar cells than to those of standard polycrystalline ones.

Electrochemical Cementation Phenomena on Polycrystalline Molybdenum Thin Films from Cu ( II ) –In ( III ) –Se ( IV ) Acidic Solutions

The electrochemical behavior of polycrystalline molybdenum thin films in contact with acidic aqueous solutions containing Cu(II), In(III), and Se(IV) species was investigated. The substrate and solutions are used for the electrodeposition of CuInSe 2 films in the field of photovoltaics. The chemical interaction between Mo electrode and the electrolyte at the initial steps of immersion is studied by in situ electrochemical measurements of the time evolution of the open-circuit potential. Ex situ field emission gun-scanning electron microscope observations for morphological investigations, X-ray photoelectron spectroscopy for surface composition, and chemical environment analysis was carried out. Raman spectroscopy, X-ray diffraction, and X-ray fluorescence were also performed. It is shown that molybdenum undergoes electrochemical cementation reactions associated with a characteristic potential increase with immersion time. Immediately after immersion, small nuclei of Cu-Se deposits appear on the surface, which then grow to form a quasi-continuous layer after 400 s. The chemical composition of the layer evolves with immersion time. No indium is incorporated. The global composition changes from a Se/Cu atomic ratio close to 0.3 to a ratio close to 0.7. The final layer contains at least two phases, i.e., umangite Cu 3 Se 2 and CuSe. These complex evolutions are discussed in terms of competing electrochemical reactions and thermodynamic considerations.

Electrochemical Growth of CuInSe2 Compounds on Polycrystalline Mo Films Studied by Raman and Impedance Spectroscopy

The growth process of Cu-In-Se compounds was investigated by in-situ electrochemical techniques and ex-situ XPS and Raman spectroscopy. The growth can be divided in three well separated steps. In a first stage, the Cu concentration is high, leading to the formation of a Cu-rich binary phase, Cu2Se, which acts as a precursor for Se(IV) reduction into elemental Se(0). When the surface concentration of elemental Se(0) is high enough, a new surface phase is formed with a stoichiometry close to CuSe2. It acts as a catalytic site for indium incorporation. This results in the formation of CuInSe2 and Cu-poor chalcopyrite phases. The proportions of the different phases evolve during the growth. This complex mechanism is in agreement with the compositional, structural and electrical properties of the samples as a function of the thickness.

Efficient Cu(In, Ga)Se 2 Based Solar Cells Prepared by Electrodeposition

CuInSe 2 and Cu(In, Ga)Se 2 precursor layers have been prepared by electrodeposition, with morphologies suitable for device completion. These precursor films were transformed into photovoltaic quality films after thermal annealing without any post-additional vacuum deposition process. Depending on the preparation parameters annealed films with different band gaps between 1eV and 1.5 eV have been prepared. The dependence of resulting solar cell parameters has been investigated. The best efficiency achieved is about 10,2 % for a band gap of 1.45 eV. This device presents an open circuit voltage value of 740 mV, in agreement with the higher band gap value. Device characterisations (current-voltage, capacitance-voltage and spectral response analysis) have been performed. Admittance spectroscopy at room temperature indicates the presence of two acceptor traps at 0.3 and 0.43 eV from the valance band with density of the order of 2. 10 17 cm -3 eV- 1 .

Electroless Nucleation and Growth of Cu–Se Phases on Molybdenum in Cu(II)–In(III)–Se(IV) Solutions

Surface reactions of molybdenum-covered glass plates, used as back contact for thin Cu(In,Ga)(S,Se) 2 solar cells, are examined at open circuit in acidic electrolytes used for plating CuInSe 2 layers. A multinary element cementation reaction occurs, leading to the corrosion of molybdenum and the formation of CuSe x electroless deposit (x from 0.2 to 0.8), with well-defined compositions. Immediately after immersion, small nuclei appear on the surface, which then grow to form a quasi-continuous layer. The time evolution of the open-circuit potential of Mo and the Se/Cu surface atomic ratio are correlated and are in agreement with thermodynamic data predictions.