Interfacial structure and current transport properties of sputter-deposited ZnO:Al/c-Si heterojunction solar cells

ZnO:Al/n-Si heterojunction solar cells were made by rf magnetron sputtering. Their interfacial structure was analysed by transmission electron microscopy (TEM). These TEM studies reveal the existence of a non-intentionally grown tunnel oxide layer between the Si wafer and the ZnO:Al film, and thus the devices are actually of the type SIS. The current transport properties of the heterojunction are investigated by means of current-voltage measurements in the temperature range 283 to 363K. Analysis of the experimental results suggests that the dominant current transport mechanism in these devices, at intermediate dark forward bias voltages, is trap-assisted multistep tunneling.