Characterization of the rear surface roughness of wet chemical polished industrial-type solar cells

PERC solar cells require smooth rear surfaces to reduce surface recombination and increase cell efficiency. State of the art surface roughness is defined solely by the polishing etch depth. However the initial texture height can vary, therefore there is no universal definition of roughness. In this work we study the rear surface roughness of industrial p-type solar cells. Different roughness parameters are presented and compared to each other and the suitability of reflection as an inline process control parameter will be shown. Subsequently, the effects of rear side roughness on the passivation quality and thus minority carrier lifetime will be discussed. A roughness optimum for multi-crystalline samples is found and therefore there is an optimal reflectance that can be controlled while processing.