Analysis and Control of Plating Baths in the Electrodeposition of Copper Indium Gallium Selenide (CIGS) Films with Ion C
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Analysis and Control of Plating Baths in the Electrodeposition of Copper Indium Gallium Selenide (CIGS) Films with Ion Chromatography Alan Kleiman-Shwarsctein, Serdar Aksu, Tuncay Cetiner, Sarah Lastella, and Mustafa Pinarbasi SoloPower Inc. 5981 Optical Court, San Jose, CA 95138
ABSTRACT Cu(In,Ga)Se2 (CIGS) is one of the most advanced absorber materials with conversion efficiencies reaching up to about 20%. Electrodeposition of CIGS precursors is highly attractive due to its low cost, efficient utilization of raw materials and scalability to high-volume manufacturing, however, a strict chemistry control of the plating baths is required in a manufacturing environment to ensure a consistent plating process with high yields. In the present study, we tested the use of ion chromatography (IC), for the quantitative analysis of both the cationic and anionic species in a variety of aqueous alkaline electroplating solutions we developed for the fabrication of CIGS precursors. Using ion chromatography we were able to precisely determine the concentrations of several key anions commonly employed in the plating baths including chloride, sulfate, selenite, selenate, tartrate, citrate, gluconate, and ethylenediaminetetraacetate. Our results indicated IC might not be a suitable method to determine the cationic concentrations for Cu, In, Ga ions when complexing species, such as ethylenediaminetetraacetate, are present in the electroplating solutions. We determined that inductively coupled plasma optical emission spectroscopy (ICP-OES) could be used instead for the precise determination of the cationic concentrations. INTRODUCTION CIGS is an advanced absorber material with a direct bandgap and a high absorption coefficient. CIGS-based solar cells have yielded the highest conversion efficiencies of all thin film solar cells, reaching up to about 20% [1]. One of the techniques used to form CIGS layers is a two-stage approach which involves deposition of a precursor layer on a substrate followed by a high temperature activation step that converts the precursor layer into solar cell grade CIGS. Although various techniques such as evaporation and sputtering have been employed to prepare precursor layers, electrodeposition is especially attractive due to its low cost, efficient utilization of raw materials and scalability to high-volume manufacturing. A wide range of processing approaches employing electrodeposition has been explored for CIGS film formation during the last two decades. The reader is referred to Lincot and coworkers [2] for a detailed review. It should be noted that most of the previous approaches concentrated on acidic electrolyte compositions. Moreover, they were generally aimed at growing CIS layers rather than CIGS films. This is partly due to the fact that addition of Ga into electrodeposited films is challenging because of the high negative plating potential of Ga compared to Cu, In and Se. Such high plating potential gives rise to excessive hydrogen evolution on the cathode surface during plating of the films out
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