We report the results of scanning laser-beam-induced current (LBIC) measurements on silicon heterojunction solar cells that indicate the length scale over which photogenerated carriers are sensitive to local defects at the amorphous silicon/crystalline silicon heterojunction interface. The defects were intentionally created with focused ion beam irradiation, enabling us to study how defects at a predefined and known location affect carrier collection and transport in neighboring regions where the device remains pristine. The characteristic length scale over which carriers in the pristine areas of the device are vulnerable to loss via recombination in the adjacent defective region increases to over 50 mu m as the device is forward biased. For photocarriers generated near the amorphous-crystalline interface, LBIC measurements suggest that lateral transport in the near-junction inversion layer in the c-Si is an important transport mechanism.