Copper Microstructure Evolution in Light-Induced Plated Metal Grids for Silicon Solar Cells: Implications for Reliable Metallization. Issue 14 (5th November 2016)

• Record Type: Journal Article
• Authors: Song, Ning; Zhang, Wei; Hsiao, Pei-Chieh; Wang, Xi; Colwell, Jack; Lennon, Alison
• Is Part Of: Journal of the Electrochemical Society. Volume 163:Issue 14(2016)
• Page Start: H1136
• Page End: H1143
• Publication Date: 2016-11-05
• Subjects: copper microstructure evolution -- Light-induced plating -- reliability; Electrochemistry -- Periodicals; 541.3705
• DOI: 10.1149/2.0441614jes
• Languages: English
• ISSNs: 0013-4651

Abstract

Abstract : Light-induced plating (LIP) presents a potentially lower-cost alternative to screen-printed silver (Ag) for front surface silicon solar cell metallization. This paper presents the results of experiments that investigated the effects of bias current density, post-plating rapid thermal processing (RTP) and electrolyte chemistry on plated copper (Cu) finger microstructure, crystal texture and resistance. It is shown that the Cu fingers, if not rapidly annealed immediately after plating, self-anneal resulting in grain growth and an increased (200) to (111) grain texture ratio which is indicative of increased tensile stress in the Cu fingers. The resistance in the fingers also decreases due to reduced scattering arising from the fewer and larger grains formed during self-annealing. The rate of self-annealing is faster with higher plating current densities and can vary for different plating electrolytes, presumably due to differing levels and types of incorporated impurities. The changes in plated Cu microstructure due to self-annealing may impact electrical reliability and adhesion of metal contacts plated using LIP for silicon solar cells where the grid geometry requirements may cause differences in the plating rate and hence self-annealing rate across a cell. Use of an RTP after Cu plating can reduce this variability with a lower and stable ratio of (200) to (111) grain texture resulting after thermal annealing, however voids can form near grain boundaries in thermally-annealed Cu fingers as they cool.