Screen-printed masking of transparent conductive oxide layers for copper plating of silicon heterojunction cells

Replacing expensive silver with inexpensive copper for the metallisation of silicon wafer solar cells can lead to substantial reductions in material costs associated with cell production. Copper metallisation is especially applicable to hydrogenated amorphous/crystalline silicon heterojunction cells since the transparent conductive oxide (TCO) layer in such cells is expected to provide an adequate barrier to prevent cell degrading copper diffusion into silicon. For copper plating on heterojunction cells it is necessary to mask the TCO surface to define the grid electrode. In this paper we investigate screen-printed masking of TCO surfaces to define copper-plated electrodes of heterojunction cells. A masking process is developed and various masking and plating aspects are evaluated. The focus of these investigations is on the characterisation of metal-TCO interfaces and on determining the influence of textured silicon wafer surfaces on the masking process. As a proof of concept, heterojunction cells are fabricated with copper-plated front contacts defined by screen-printed TCO masking. The copper-plated heterojunction cells achieve conversion efficiencies comparable to reference heterojunction cells with evaporated front contacts defined by photolithography.