Against the backdrop of persistently high silver prices, silver paste further increases the cost pressure on crystalline silicon and tandem solar cells. There is an urgent need to develop low-silver or silver-free conductive pastes with lower costs to achieve the goals of reducing costs and improving efficiency in solar cells. Among these, replacing silver powder with silver-coated copper powder is currently one of the most effective cost-reduction solutions for conductive pastes. Silver-coated copper paste not only achieves electrical performance comparable to that of silver paste but also significantly reduces costs due to its lower silver content. Moreover, it exhibits better continuous oxidation resistance and long-term reliability. As a result, it has become a key material for the metallization of crystalline silicon solar cells and tandem solar cells.
Silver-coated copper powder typically consists of spherical microparticles with a particle size of 1.0-7.0 μm and exhibits high packing porosity. Therefore, achieving ideal conductivity requires the assistance of submicron silver powder for improved packing and nano-silver powder to promote low-temperature sintering. However, driven by the industry trend toward silver reduction, finding alternatives to nano-silver powder is of great significance for further cost-effective optimization of paste performance. Conductive nano-oxide powders exhibit high surface energy, high electrical conductivity, and high melting/boiling points, along with low shrinkage, making them a viable candidate material to substitute for nano-silver powder. Nano-antimony tin oxide (ATO) powder, as a typical n-type semiconductor material, belongs to the same semiconductor type as the window layer of SHJ(Silicon Heterojunction) or tandem solar cells. It easily forms ohmic contacts when in contact with silver-coated copper powder or silver powder and has low resistivity. Compared to expensive nano-silver powder, its cost-effectiveness is particularly outstanding.
This study aims to improve the sintering behavior and conductivity of low-temperature silver-coated copper paste by adding high-surface-energy nano-ATO powder. Using SHJ solar cells as the subject, the application effects and mechanisms were systematically investigated. The influence of nano-ATO was analyzed in terms of the paste's thermodynamic properties, rheological behavior, electrical performance, and corresponding cell performance. The main conclusions are as follows:
(1) When the ATO content is ≤1.5%, it effectively reduces the volatilization temperature of solvents during the curing process, minimizes solvent residue, and thereby promotes powder sintering and resin curing.
(2) As the ATO content increases, the rheological properties of the paste, such as thixotropy, yield stress, and elastic modulus, are enhanced. The static paste structure is strengthened, which helps suppress sagging and enables narrower and more stable printed line widths.
(3) The bulk resistivity of the paste initially decreases and then increases with increasing ATO content, while the contact resistivity between the electrode and the substrate continues to decrease with higher ATO content.
(4) ATO powder helps reduce the distribution of organic resin at the contact interface, thereby improving the open-circuit voltage. Additionally, it supports finer grid lines, which enhances the short-circuit current. The series resistance of the cell first decreases and then increases with increasing ATO content.
Driven by the synergistic effect of the above factors, the efficiency of the SHJ cell reaches its maximum when the ATO addition is 1 wt.%, representing a relative improvement of 0.485% compared to silver paste. This indicates that an appropriate amount of nano-ATO powder can effectively enhance the overall conductivity of the paste, thereby significantly improving the comprehensive performance of the cell.