Passivation of Inline Wet Chemically Polished Surfaces for Industrial PERC Devices

We study the impact of the residual surface morphology resulting from rear side wet chemical polishing of initially random pyramid textured surfaces on large area industrial rear surface thermal oxide passivated Cz Si solar cells. Cell parameters for three different surfaces (low, medium and high removal of Si) and a fully textured rear surface as reference are presented for solar cells with rear sides metallized either by physical vapour deposition or by screen printing technique. For both metallization schemes a flattened surface clearly results in higher values for open circuit voltage and short circuit current density and thus also cell efficiency. Median efficiencies up to 19.4% (239 cm2, as processed) and stabilized peak efficiency of 19.3% (confirmed by Fraunhofer ISE CalLab) are reached. Carrier lifetime and quantum efficiency measurements confirm that the rear surface recombination and injection dependence strongly reduces for flattened surfaces, which is attributed to changes in crystal orientation and reduced surface area.