In-situ n-type doping by screen-printed aluminum paste for back contact silicon solar cells

The self-doping contact concept integrates junction or back surface field (BSF) formation with metal contact deposition in a single step. This approach is particularly well-suited to addressing patterning complexity in back contact (BC) silicon (Si) solar cells. Previous studies have demonstrated silver (Ag)-based self-doping pastes, but the associated cost remains a major limitation. In this work, we present a low-cost alternative based on a modified aluminum (Al) paste, which facilitates in-situ formation of n + regions on Si substrates. For p-type substrate, the modified Al paste enables in-situ formation of the n-type emitter, and the emitter exhibits a thickness of ∼0.4 μm and a peak doping concentration of 1.2 × 10 19 cm −3 . For n-type substrate, an n + BSF is achieved, reaching a doping concentration of 1.0 × 10 20 cm −3 within a depth of ∼0.2 μm. The contact properties between this work Al pastes and Si layers are first investigated. In addition, the doping mechanisms of the modified Al paste were systematically studied under various firing conditions. This work enables a simplified Ag-free self-doping process for fabricating both n-type and p-type BC solar cells, eliminating the need for traditional phosphorus diffusion. • A modified Al paste was developed for the first time to enable in-situ formation of n + regions on both p-type and n-type Si wafers. • The paste forms an in-situ n + emitter (∼0.4 μm) with 1.2 × 10 19 cm −3 on p-Si, and an n + BSF (∼0.2 μm) 1.0 × 10 20 cm −3 on n-Si. • The contact properties of such modified Al-based paste were evaluated for the first time. • The concept of “doping dominance” was introduced to explain the n + /p + transition as a function of modifier content and thermal budget.