A scanning tunneling microscope in ultrahigh vacuum is used to measure the profile of electronic properties of cleaved amorphous silicon solar cells. Their exposed layers in a single and a tandem cell can be identified by their characteristic current—voltage dependencies (scanning tunneling spectroscopy). An “Apparent Potential” is measured throughout the cells. The results for the tandem cell from SOLAREX, Inc. are shown. ©1999 American Institute of Physics.