Indium Reduction Above 70% in SHJ Solar Cells: Study of the Module Stability

Abstract

This work focuses on reducing In-based TCO thicknesses to their minimum in SHJ solar cells with the goal to demonstrate the possibility of a drastic reduction of indium consumption in the fabrication process. On the front side, the reduction of the ITO thickness down to 15 nm implies to deposit an additional anti-reflective layer. Three anti-reflective dielectric layers have been studied (SiN_x, SiO_x and a bilayer SiN_x/SiO_x) in solar cell and module configurations to maximize the performances and evaluate the module stability under UV exposure. Lower J_sc losses after 120 kWh of UV exposure are measured with the use of thinner ITO layers, in agreement with a lower EQE deterioration in the IR range. The use of SiN_x dielectric results in the highest stability under UV and to the best performances after 120 kWh. Following further optimizations of the dielectrics and TCO, the 15 nm of ITO/SiN_x option was combined with a thin IMO:H TCO on the rear side. TCO thicknesses down to 30 nm were studied on the rear side resulting in overall indium reduction of 77.2% with very limited efficiency loss at the cell level (below 0.1% absolute after light-soaking). Module reliability of these very low indium content solar cells was studied under UV and damp heat treatments highlighting lower degradations than reference cells for UV and promising results after damp heat test.