Effect of the mass ratio of micron and submicron silver powder in the front electrode paste on the electrical performance of crystalline silicon solar cells

Abstract

In this paper, highly-dispersed spherical micron-sized (D₅₀ = 2.94 μm) and submicron-sized (D₅₀ = 0.59 μm) silver powders were prepared by a chemical reduction method. Hybrid silver powder was then synthesized by mixing the micron- and submicron-sized silver powders, and the mass percentages of submicron-sized silver powder in the hybrids were 0, 100, 5, 10, 15, and 20%. The tap density of the silver powders, cross-sectional and surface microstructures, and performance of cells designed using these silver powders were investigated. The results suggested that the mass ratio of hybrid silver powder had an important influence on the structure of the contact interface, the quality of the ohmic contacts, and the electrical performance of solar cells. The electrical performances of solar cells made with mixed silver powder were better than those made using pure micron- or submicron-sized silver powders. The optimal level of submicron-sized silver powder content was 15 wt%. This was because the surface morphology of the thick films prepared using this hybrid was smooth and dense, the layer had sufficient silver crystallites to increase the contact area fraction, and there was a thin glass layer to improve the probability of tunnelling from Ag crystallites to the Ag grid. This led to the formation of good ohmic contacts and conductive chains. As a result, this silver powder gave the best photoelectric conversion efficiency (18.282%) and series resistance (0.0019 Ω).