Feasibility test of drastic indium cut down in SHJ solar cells and modules using ultra-thin ITO layers

Abstract

In this work, we investigate the possibility to drastically decrease the indium (In) consumption in silicon heterojunction (SHJ) solar cells, using ultrathin (<15 nm) ITO layers on both cell sides, in combination with SiN:H capping dielectric layers. The best ITO/dielectric combinations were assessed using optical simulations. The optimal stacks were integrated on front, rear, and both sides of complete SHJ cells. Two types of nanocrystalline layers (nc-Si:H and nc-SiOx:H) were implemented as selective layers on the front side, and proved to relax the constraints on the front ITO conductivity. Among all conditions including 100 nm references, the highest module efficiencies were obtained with 15 nm front ITO (22.4%), while modules with ITO layers below 10 nm on nc-Si:H showed very low efficiency losses compared to the reference. Integration of such ultrathin ITO layers on the rear side proved to be non-optimal since the Fill Factor (FF) losses are not counterbalanced with current gains (contrary to what is observed on the front side with ultra-thin ITO). Finally, UV reliability tests were performed and showed an enhanced reliability for modules with thinner ITO layers. After 60 kW h.m−2 of UV exposure, modules with 5 nm ITO on nc-Si:H showed the best efficiencies among all tested conditions. Subsequent damp heat tests were also performed and did not show a clear warning against using ultrathin ITOs on the front side, and in the end, modules with nc-Si:H layers feature the highest efficiencies at the end of the reliability sequence.