Surface and interface properties of CdTe/CdS/SnO2/glass heterojunction solar cells are studied by means of x‐ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and optical reflectance (OR) techniques. First,n‐type CdS layer was grown by solution growth technique on the SnO2coated glass substrate and then thep‐type CdTe was deposited on CdS by metal‐organic chemical‐vapor deposition. Despite many other efficiency limiting mechanisms in CdTe solar cells, this article shows that surfaces and interfaces play an important role in determining the cell efficiency. In an attempt to correlate the surface and interface properties to the cell performance, a series of CdTe/CdS solar cells with different conversion efficiencies were fabricated and analyzed. It was found that high efficiency cells possess Te‐rich CdTe surface along with smooth interfaces, as revealed by XPS, SIMS, and OR measurements, while low efficiency cells display near stoichiometric or Cd‐rich CdTe surface and abrupt interfaces. The impact and role of interface/surface properties on CdTe solar cell performance are discussed. ©1996 American Institute of Physics.