From the Lab to Scaling-up: Case Studies of Electrodeposition Processes in the Photovoltaic Industry

Photovoltaic (PV), with more than 300 GW of cumulative capacity installed by the end of 2016, represents about 1.5% of the world electricity production. It is now obvious that the growth of PV will not only continue but even accelerate, as a key player for the energy transition, reaching up about 5 TW by 2050, as projected by the International Energy Association. The main reason for this development is due to a reduction by 10 of PV electricity cost in ten years. This trend makes PV electricity competitive with classical fossil or nuclear electricity in many regions of the world. The decrease in cost has resulted from improvement in materials and methods, an increase in solar energy conversion efficiency and in volume production. Research and Development plays a major role in this process proposing innovation and scientific breakthroughs in existing PV technologies and introduction of new technologies. Scaling effects have played a key role in decreasing the production costs but further progress along with innovative technologies will be needed to lower costs. The comparison between thin film technologies and wafer based technologies is typical of this paradigm. Thin film technologies are basically coating technologies which are inherently better adapted for large area processing (thousands of km 2 ) compared to slicing individual crystalline wafers and assembling them as a mosaic. However, any defect on a part of a large area process induces a huge impact on the whole panel where the slices of Silicon are sorted to produce module. Moreover, the cost reduction of the wafer technology with scaling and the industrial maturity of silicon technology is so rapid that this technology is cost leading. As a consequence, the PV industrial sector is dominated at more than 90% by Silicon solar cells. The remaining 10% is composed of vacuum based thin films. Electrodeposition, despite intrinsic advantages, with real success in industry with, among numerous other examples, damascene copper in semiconductor or permalloys in thin film head, is almost absent of this PV industrial landscape. However, introduction of plating will be easier and more probable for new cell technologies, where new investment has to be done and for which stringer requirements emerge. In this context, we will discuss and make some prospective about two case studies involving electrodeposition in PV: plating contacts on Silicon and Cu-In-Ga based plating for thin films solar cells. On Silicon PV market, Copper represents an alternative to Silver screen printing. Copper has a much lower price than Silver with an equivalent bulk resistivity. Interdigited Back Contact (IBC) and Heterojonction (HJT) solar cells with Cu plating already exists for years. Nonetheless, Cu being a lifetime killer in c-Si, a Ni diffusion barrier is usually used. This approach has been demonstrated for front side metallization, based on Light Induced Plating. The case of emerging bifacial solar cells will be specifically discussed with the use of Ni/Cu or Ni/Ag plating. The remaining challenges will be discussed, including specificity of plating on both sides simultaneously, surface roughness issue and his impact on adhesion, ghost plating linked to surface passivation defects. For producing thin film solar cells, an alternative to vacuum based deposition methods (co evaporation, sputtering), which are presently used, is to use electrodeposition or printing. We will make a comprehensive description of the scale-up of the electrodeposited CIGS precursor layers from the laboratory scale of a rotating disk electrode to a full-size 60 cm x 120 cm compatible with 1 m 2 /min production of solar panels. More specifically, we will discuss the different fabrication approaches for electrodeposited precursor CIGS materials, development and recycling of solution chemistries for Copper, Indium and Gallium. Resulting fabrication of solar cells will be described. We will also present applications and devices which specifically take advantage from electrodeposition approach that is localized deposition on patterned substrate. The specific mechanism of electrodeposition in microelectrode array configuration and the challenge of upscaling will be discussed. References L. Tous et al, Energy Procedia 124, 922–929 (2017). Q. Huang, et al, Journal of The Electrochemical Society, vol. 158, issue 2, 2011, D57-D61 P.-P. Grand et al, WO 2012/052657 C. Broussillou et al, IEEE, New Orleans (2015) A. Duchatelet et al, Applied Physics Letters, 109 (2016), 253901