O. Kerrec

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.

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.

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.