Silicon Heterojunction Solar Cells With Copper-Plated Grid Electrodes: Status and Comparison With Silver Thick-Film Techniques
Copper electroplating is investigated and compared with common silver printing techniques for the front metallization of silicon heterojunction solar cells. We achieve smaller feature sizes by electroplating, significantly reducing optical shadowing losses and improving cell efficiency by 0.4% absolute. A detailed investigation of series resistance contributions reveals that, atmaximum power point, a significant part of the lateral charge-carrier transport occurs inside the crystalline bulk, rather than exclusively in the front transparent conductive oxide. This impacts optimization for the front-grid design. Using advanced electronmicroscopy, we study the inner structure of copper-plated fingers and their interfaces. Finally, a cell efficiency of 22.4% is demonstrated with copper-plated front metallization.