Electrodeposited Cu-In-Ga-Se Thin Films for CIGS-Based Solar Cells
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1165-M02-04
Electrodeposited Cu-In-Ga-Se Thin Films for CIGS-Based Solar Cells Raghu N. Bhattacharya National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401 ABSTRACT Cyclic voltammogram studies were performed on H2SeO3, CuSO4, In2(SO4)3, GaCl3, H2SeO3 + CuSO4 + In2(SO4)3 and H2SeO3 + CuSO4 + In2(SO4)3 + GaCl3 to understand the electrodeposition mechanism. The reduction potential from the cyclic voltammogram studies indicates that the first deposited layer is Cu from the Cu-In-Se and Cu-In-Ga-Se solution mixture. The subsequent deposition of the In and Ga layer is more favorable on the firstdeposited Cu layer. INTRODUCTION Solar cells are a very attractive source of clean energy. CuIn1-xGaxSe2 (CIGS) has the potential to become a major candidate in this field. Its large optical absorption coefficient, which results from a direct energy gap, permits the use of thin layers (1−2 µm) of active material. Currently, a great deal of effort is being expended to develop low-cost technologies for fabricating CIGS thin films [1-5]. The physical vapor deposition method is an excellent tool for understanding film growth and for developing models, but is challenging to scale up. Sputtering techniques are suitable for large-area deposition, however, they require expensive vacuum equipment and sputtering targets. Electroplating is a potentially suitable preparation method to obtain low-cost precursor films. The electrodeposition process could provide: (a) high-quality film with very low capital investment; (b) a low-cost, high-rate process; (c) use of very low-cost starting materials (e.g., low-purity salts, solvents), based on automatic purification of the deposited materials during plating; (d) a large-area, continuous, multi-component, lowtemperature deposition method; (e) deposition of films on a variety of shapes and forms (wires, tapes, coils, and cylinders); (f) controlled deposition rates and effective material use (as high as 98%); and (g) minimum waste generation (i.e., solution can be recycled). Devices fabricated using electrodeposited CIGS precursors resulted in an efficiency of 15.4% [1]. In this paper, the deposition mechanism of electrodeposited CIGS layers is described.
EXPERIMENT AND DISCUSSION Electrodeposition is a process for depositing a coating with uniform coverage and properties on conducting substrates from a solution containing the ions of interest. In a solution containing Cu2+, In3+, Ga3+, and H2SeO3, all four ions can be codeposited on the surface of the substrate when the potential is sufficiently negative. In cathodic electrodeposition, when the potential of the substrate (electrode) is moved from its equilibrium value toward negative potentials, the cation that will be reduced first is the one with the least negative (or most positive) redox potential E0. To determine the deposition potential of individual elements, a cyclic voltammogram experiment of H2SeO3, CuSO4, In2(SO4)3, GaCl3, H2SeO3 + CuSO4 + In2(SO4)3
and H2SeO3 + CuSO4 + In2(SO4)3 + GaCl3 was performed. The cathode a
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