In-situ formation of indium seed layer for copper metallization of silicon heterojunction solar cells

Abstract

Low production cost and simplified process are the prerequisites for large-scale commercialization of highly efficient silicon heterojunction (SHJ) solar cells. In this paper, an innovative method of plating process with in-situ seed layer technique is proposed for the metallization of SHJ solar cells. As indicated by the measurements of cyclic voltammetry curves and scanning electron microscopy, electrochemical reduction reaction occurs and results in metal particles randomly distributed on the surface of tungsten doped indium oxide (IWO) layer. Given the measurement of Energy-dispersive X-ray spectroscopy elemental mapping and X-ray photoelectron spectroscopy, the metal particles are indium and are electrochemically reduced from the IWO film. These indium particles can serve as the seed layer facilitating the subsequent copper plating process. In order to prevent copper diffusion and enhance the adhesion, nickel plating and alkaline copper plating was applied. As a result, the maximum peeling force of plated copper busbar reaches 4.23 N. This is higher than that of the screen-printed silver busbar (2.31 N). By adopting the in-situ indium-seed-layer based plating process, a cell efficiency of 22.01% was achieved with significantly improved short circuit current density and fill factor. Taking advantage of the in-situ seed layer technique, the all-solution based plating process is simplified and effective without full area seed layer deposition and subsequent etch back step, showing great potential for the copper metallization of SHJ solar cells with reduced cost.