Dual‐Function Light‐Trapping: Selective Plating Mask of SiOx/SiNx Stacks for Silicon Heterojunction Solar Cells

Abstract

Reducing the production cost of highly efficient silicon heterojunction (SHJ) solar cells is essential for their large‐scale commercialization. Replacing screen printed silver contacts with plated copper is an effective way. However, one needs to deal with the process compatibility without sacrificing the cell performance. In this work, a layer stack of silicon oxide and silicon nitride (SiOx/SiNx) is proposed, serving dual functions of light‐trapping and selective copper plating mask. The SiOx/SiNx stack is prepared by plasma enhanced chemical vapor deposition (PECVD) on a tungsten doped indium oxide (IWO) layer. Optimized SiOx/SiNx/IWO stacks in SHJ solar cells with silver contacts result in excellent anti‐reflection properties and improved external quantum efficiency. A short circuit current density gain of 1.16 mA cm−2 is achieved without the loss in fill factor. This SiOx/SiNx stack is tested as in‐situ deposited selective plating mask for a front‐side copper plating process. An in‐house made light induced plating tool is utilized. A screen printed silver finger is applied as a seed layer for copper plating. The bulk resistivity of Cu/Ag finger reduces to 4.1 E‐6 Ω · cm, which is lower than that of low temperature silver paste (around 6 E‐6 Ω · cm) before copper is plated on it. The dual functions of SiOx/SiNx stack and the process are proven, indicating a good potential for further improving photoelectric properties of SHJ solar cells after well optimization.