Photoluminescence (PL) imaging is a fast and contactless technique that allows visualizing defective regions of a solar cell where local carrier lifetime is reduced. In this paper we present a PL based method for the quantification of such defective areas in the case of a-Si:H/c-Si heterojunction solar cells produced in an industrial pilot line. After a description of the methodology used for obtaining a " defectivity parameter " G d from the open-circuit PL images, we show that the efficiency of non-metallized cells produced in this line can be predicted from their G d value with absolute deviations lower than 0.2%. Numerical calculations based on the two-diodes model are then used together with experimental results to investigate the impact of the defective regions on the cells performance. Finally, we focus on some defective regions using high resolution characterization tools such as SEM, EDX and m-PL, and show that they can emanate from microscopic defects induced by the wafering step.