Low-Ag electrically conductive adhesives for cost-effective circuit interconnection in advanced module applications

The photovoltaic (PV) industry is currently exploring low-temperature joining processes to avoid the solar-cell structural damage often incurred during the high-temperature, flux-based soldering methods traditionally used for cell interconnection in PV modules. High-efficiency solar cells, such as the heterojunction technology (HJT) and tunnel oxide passivated contact (TOPCon) solar cells, are particularly susceptible to significant cell degradation when exposed to elevated temperatures. Consequently, there is a critical need for low-temperature interconnection processes operating below 150 °C. Electrically conductive adhesives (ECAs) cured at low temperatures have emerged as a prominent solution to meet this requirement. However, the adoption of conventional ECAs is significantly limited by their composition, which typically contains silver (Ag) at levels exceeding 80 wt%, resulting in increased cost for commercial application. In this work, we developed and benchmarked six Ag-lean ECAs (ECA #1–#6, 54–70 wt% Ag) and introduced a binder-optimized variant (ECA #2-1) by incorporating an aliphatic urethane–acrylate oligomer. These formulations were then comparatively evaluated against a commercial ECA reference containing 80 wt% Ag. We performed a multimodal analysis (including Fourier-Transform Infrared Spectroscopy (FT-IR), Thermo-Gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), rheology, Field-Emission Scanning Electron Microscopy (FE-SEM), and resistivity measurement) to elucidate the composition–microstructure–performance relationship of Ag-lean ECAs (#1–#6). The baseline formulations exhibited critical trade-offs; for instance, ECA #3 achieved the lowest resistivity (~7×10⁻⁵ Ω·cm) but exhibited poor thermal stability and processability. In contrast, the binder-optimized ECA #2-1 demonstrated enhanced network density and contact consolidation, fulfilling all key requirements: low-temperature curing ( T ₚ ≈ 85–88 °C), high thermal stability ( T 5 ≈ 355–365 °C), balanced shear-thinning rheology, and competitive resistivity (8.51 × 10⁻⁵ Ω·cm). Additionally, the shingled strings, fabricated by interconnecting cut solar cells using ECAs, demonstrated power output and fill factor (FF) values comparable to those of a commercial reference. Our Ag-lean formulations exhibit significant potential, offering a viable pathway to low-cost, high-performance interconnection materials for advanced photovoltaic applications.