Copper metallization of electrodes for silicon heterojunction solar cells: Process, reliability and challenges

The crystalline silicon (c-Si) based technologies occupy 95% market share in the global photovoltaic (PV) production capacity. The conversion efficiency of silicon heterojunction (SHJ) solar cell in mass production has gone beyond 23%. The most pressing challenge hindering the industrial scale expansion of SHJ solar cell currently is the relatively high production cost as compared to the PERC (passivated emitter and rear cell) product. The low temperature silver paste utilized in the SHJ cell process accounts significantly for about 30% of the total processing cost due to its large consumption. Copper plating is of great current interest to silicon heterojunction application, which has a high potential to cut down the cost and improve cell efficiency by the remarkably reduced shading loss, increased electrode conduction and fill factor. However, there are still some critical issues need to be systematically optimized and proven for mass production. Selectively-deposited seed layer and stripping-free plating resist are the key factors to simplify the plating process. This paper gives a detailed look into the development of copper metallization for SHJ solar cell. Plating process involving seed layer formation and patterning methods are explicated. The process simplification and reliability are discussed aiming at its employment in industrial production.