PASHA: A new industrial process technology enabling high efficiencies on thin and large mc-Si wafers

To maintain high efficiencies for solar cells and reduce the cell bowing, the full Al rear surface of thin conventional solar cells has to be replaced by a more suitable passivating rear surface layer. In our new PASHA-cell (Passivated on All Sides H-patterned cell) we apply a single silicon-nitride (SiNx:H) layer for rear surface passivation in combination with an open, firing through aluminum metallization. This improved processing results in a gain in efficiency of almost 1% absolute compared to full Al BSF, achieving 16.4% on 156 cm², 200 μm thick mc Si solar cells. Besides this efficiency gain, due to lower consumption of aluminum, there will be a reduction in the costs of cell fabrication. Furthermore, the severe bowing of wafers thinner than 200 μm has been reduced to zero. To test the industrial stability, the processing was applied on a batch of large (243 cm²) and thin (160 μm) wafers which yielded an average cell efficiency of 15.5% with a maximum of 16.1%. This is 0.5% absolute better than the full Al rear reference, even though the rear metallization pattern has not been optimized yet.