Electrodeposition of Copper, Selenium, Indium, and Gallium on Molybdenum/Surface Oxides: Unary, Binary, Ternary and Quaternary Compositions

Abstract

A systematic investigation was performed to study the variation of cyclic voltammetry (CV) peaks during cathodic electrodeposition of unary, binary, ternary and quaternary compositions of copper (Cu), selenium (Se), indium (In) and gallium (Ga) on molybdenum/glass electrode. The major objective of the work was to methodically understand the variation of different oxidation-reduction peaks from unary to quaternary composition so that a comprehensible idea on their appearance could be arrived. The electrodeposits were further characterized by anodic stripping voltammetry and frequency response analyzer-impedance spectroscopy. Phase and microstructure of the electrodeposits were examined by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The results presented were helpful to arrive at new conclusions on the variation of different CV peaks such as Mo/surface oxide'scharacteristic redox peak and In-characteristic oxidation peak. The present work will be of significance in different application areas like surface coatings, electronics and chalcopyrite solar cells, where electrodeposited Cu-Se-In-Ga is of importance.Electrodeposition has been widely investigated as a simple and economic alternative to the vacuum deposition techniques in fabricating various industrially important materials in thin film and bulk dimensions. 1-4 Electrodeposition of unary, binary, ternary and quaternary compositions of copper (Cu), selenium (Se), indium (In) and gallium (Ga) has a wide range of applications. 1-8 Cu electrodeposition on foreign substrates plays a key role in electronic industry 1 and protective/decorative coatings. 2 Electrodeposition of trigonal Se and compound semiconductors of Se have a variety of interesting applications in solar cells, rectifiers, medical diagnostics and xerography. 4 In has been widely used in alloys, 5 electronics and catalytic organic synthesis. 6 Ga is important in semiconductor and electronics industries due to its unique electrical and thermal properties. Ga plays an important role in achieving high efficiency chalcopyrite solar cells. 3,7,8 One-step electrodeposition was widely investigated for growing large area polycrystalline CuInSe 2 /Cu(In x Ga (1-x) )Se 2 (CIS/CIGS) films on molybdenum (Mo) at potentials as high as −0.90 V (vs. Ag/AgCl). A number of studies have investigated the mechanism of deposition of ternary CIS 9-17 and quaternary CIGS. 13,18-22 Proper understanding of voltammetric behaviors of individual elements and their variation on moving from unary to quaternary composition is vital in optimizing the deposition parameters and elucidating the deposition mechanism. Recent reports demonstrated the potential of electrodeposited ternary and quaternary chalcopyrite absorber layers for various solar energy conversion devices. [23][24][25][26] In spite of a good number of investigations on the electrodeposition of Cu, Se, In and Ga and the various compositions on different electrodes, 1-4,7-46 several concepts and explanations on the origin of differ...

Electrochemical Atomic Layer Deposition of CuIn(1-x)GaxSe2on Mo Substrate

“…The standard reduction potential of Ga 3+ /Ga is −0.722 V (vs. Ag/AgCl). During negative going scan, the onset of reduction current appeared at −0.64 V, and a sharp reduction peak of C 1 was found at −0.806 V. 42,45,46 This reduction potential could lead to bulk reduction of Ga 3+ /Ga. The potential for Ga 3+ deposition in this experiment was chosen as −0.75 V, positive from the potential of C 1 .…”

“…The peak C 2 could be possibly by bulk reduction of In 3+ /In on Mo substrate. [42][43][44] From C 2 deposition region, −0.70 V was selected as the potential of E-ALD for In 3+ in this experiment. Figure 4 shows the CV studies of Mo electrode in Gallium (III) solution of 1 mM Ga 2 (SO 4 ) 3 · xH 2 O and 0.1 M Na 2 SO 4 at pH 3.…”

“…They achieved different stoichiometry films on different alternate sequencing and superlattice sequencing by depositing a different number of periods or 38 Although CIGS film with classic stoichiometry was achieved on model Au surface by means of E-ALD, it would be interesting with application perspective to find whether a similar film by the method can be prepared on the practical surface of Mo, which is often the choice of the substrate for CIGS solar cells and yet the complex substrate in the ambient laboratory conditions because of the surface oxides formed. 4,6,39,42 In this work, we wish to present that the chalcopyrite CIGS thin films were successfully grown by E-ALD technique of superlattice sequencing the binary compounds of 2InSe/2GaSe/1CuSe on Mo electrode. The synthesized film was characterized to be chalcopyrite CIGS by XRD, SEM, STM and EDS, and the E-ALD film was shown to be photoelectrochemically active with p-type conductivity.…”

A short review on the advancements in electroplating of CuInGaSe2 thin films

“…Though increasing the concentrations of In(III) and Ga(III) shifts the potential closer to Cu(II) [53], excessive currents generated due to high bath concentrations may cause significant pitting and corrosion of Mo/glass substrates [54]. Recent impedance studies by Saji et al also verified that excessive In ions can interact or complex with Mo/surface oxides and that in effect can cause a certain extent of Mo dissolution [55]. Electrodeposition at high cathodic potential conditions affects the In and Ga plating efficiency due to the parallel occurrence of hydrogen evolution, which is considered to be the origin for film inhomogeneity and pin holes formation.…”

“…Since then, several works on electrodeposition of CISe/CIGSe using TEA have been reported as it can form strong complexes with Cu 2+ and HSeO 2- , and 4.5 mM Se 4+ ions in the bath at a pH of 2.5. The electrolyte was stabilized using a buffer of pH 3 (pHydrion mixture of sulphamic acid and potassium biphthalate) along with LiCl as supporting electrolyte [55]. Recent works by Liu et al have suggested that by increasing the sodium sulfamate concentration, (Cu + Se)/ (In + Ga) decreases, while gallium content increases and the film composition transforms from Cu rich to Cu poor [58].…”