Effect of Active Al on the Microstructure and Mechanical Properties of a Mo/Sn-Based Solder Interface: First-Principles
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https://doi.org/10.1007/s11664-020-08429-8 Ó 2020 The Minerals, Metals & Materials Society
Effect of Active Al on the Microstructure and Mechanical Properties of a Mo/Sn-Based Solder Interface: First-Principles Calculation and Experimental Study HAO LIU,1 WEIBING GUO,1,2,3 HAITAO XUE,1 and XIAOMING ZHANG1 1.—School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300401, China. 2.—State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001, China. 3.—e-mail: [email protected]
In this work, Sn-based active alloys were used to solder a Mo electrode and Al together, and the effect of active Al on the Mo/solder interface was studied with methods of first-principles calculation and experiments. The Mo(110)/ Sn(001) interface with bridge site was found to have the largest work of adhesion (Wad). The heat of segregation (DGseg) results reveal that Al atoms prefer to diffuse to the interface and form bonds with Mo, resulting in the AlMo intermetallic compound (IMC) layer. When two Al atoms appear at the interface, the value of Wad increases to 3.02 J/m2 dramatically, which indicates that Al strengthens the Mo/Sn interface. Then pure Sn, Sn-9Zn, Sn-9Zn2Al, and Sn-13.5Zn-10Al alloys were prepared to solder Mo and Al assisted by ultrasound. Pure Sn and Sn-Zn solders have weak bonding with Mo, and the joints fractured from the interface with very low strength. When the Sn-9Zn2Al and Sn-13.5Zn-10Al solders were used, the active Al segregated to the interface and reacted with Mo. The interface was strengthened by the Al-Mo IMC layer. The joints fractured inside the solder layer, and the shear strength of joints using Sn-13.5Zn-10Al reached 35 MPa. Key words: Mo, active solder, first-principles calculation, microstructure, mechanical property
INTRODUCTION The Cu(In,Ga)Se2 (CIGS) thin-film solar cell has attracted increasing attention due to its excellent properties of low price, low radiation damage, longterm stability, high absorption coefficient, and tunable band gap.1 It has been reported that the efficiency of the CIGS solar cell has reached more than 20% in many groups.2 The structure of the CIGS solar cell is ZnO:Al/ZnO/CdS/CIGS/Mo/substrate. The Mo thin film has low contact resistance and good chemical stability by the formation of a Mo2Se compound layer. Therefore, Mo film acts as the rear contact for the CIGS solar cell.3 The output voltage of a single CIGS solar cell is very low. To
(Received February 28, 2020; accepted August 17, 2020)
obtain higher open-circuit voltage, the rear contact of the cell must be bonded with the top contact of another cell to form a solar power module.4 The Mo layer acts as the back electrode for the CIGS solar cell, and two cells must be joined through Al interconnector ribbons. Therefore, it is of great importance to join Mo and Al together. The soldering process is widely used in the packaging of solar cells. High joining temperature deteriorates the performance of solar cells for higher interface stress. Therefore, l
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