In the field of solar cell technology, the conversion efficiency of silicon heterojunction (SHJ) solar cells has reached 27.08%. Meanwhile, perovskite/SHJ tandem solar cells based on this structure have achieved an efficiency of 34.85%, exceeding the theoretical limit of 33.7% for single-junction devices. In the industry transitions from single-junction to tandem configurations, SHJ cells, due to their unique structure and low-temperature fabrication process, exhibit superior compatibility with perovskite layers. This makes SHJ technology play a critical role in the development of perovskite/tandem solar cells.

The application of high-performance silver-coated copper (Cu@Ag) paste to electrode metallization provides a feasible method to reduce the costs and improve the performance of SHJ cells. However, the micron-scale particle size of Cu@Ag powder (typically several micrometers) limits the packing density of the electrode layer. To address this, nano-silver powder (about 100 nm) is commonly used as an additive, which enhances both the packing density of the powder and the electrical conductivity through nano-effects. Although many studies focus on isolated aspects such as paste conductivity, a systematic evaluation covering contact resistivity, printed and cured electrode morphology, overall cell performance, and long-term stability remains scarce. Potential adverse effects of nano-silver addition have also been overlooked. Therefore, a thorough investigation on the role of nano-silver in low-temperature Cu@Ag pastes is necessary.

Highly conductive low-temperature curing pastes generally use binary or ternary composite powders with well-separated particle sizes to achieve high packing density according to the dense packing theory. In this work, we systematically adjust the proportions of three conductive powders: micro-sized Cu@Ag (3—5 μm), sub-micron silver (500 nm), and nano-silver (100 nm), to study the effects of nano-silver on key properties of Cu@Ag paste. These include curing temperature and sintering behavior, microstructure of cured electrodes, interface structure between electrodes and the silicon wafer, electrical resistivity, and the overall conversion efficiency of SHJ solar cells. The aim is to clarify the underlying mechanisms and optimize the nano-silver content.

This research reveals several significant influences of nano-silver addition on Cu@Ag paste properties. 1) It markedly reduces the resistivity of the cured electrode. Compared with sub-micron silver, nano-silver facilitates improved lateral conductivity at lower sintering temperatures. 2) It introduces additional pores at the contact interface with the silicon wafer, thereby increasing contact resistivity. A thickened organic layer at the interface also forms, which reduces the open-circuit voltage of the cell. 3) It enhances paste thixotropy, resulting in narrower printed electrode lines to reduce shading loss and increase short-circuit current density. At the same time, it raises electrode height and cross-sectional area, which helps improve the fill factor. 4) When the nano-silver content is controlled at 15%, the efficiency of SHJ cells is comparable or close to that of reference cells with pure silver electrodes, mainly due to the improvement of fill factor and short-circuit current density.

In summary, an optimized amount of nano-silver powder (e.g., 15%) can simultaneously enhance electrode conductivity, printability, and opto-electrical performance, resulting in SHJ cells with efficiency comparable to those using pure silver electrodes. This demonstrates the potential of Cu@Ag pastes as a cost-effective alternative without compromising performance. Future studies should focus on the long-term reliability of such paste and its scalability, which will support the mass adoption of this technology in various tandem solar cells.