The nature of the interface between CuInGaSe2 (CIGS) and the chemical bath deposited CdS layer has been investigated. We show that heat-treating the absorbers in Cdor Zncontaining solutions in the presence of ammonium hydroxide sets up an interfacial reaction with the possibility of an ion exchange occurring between Cd and Cu. The characteristics of devices made in this manner suggest that the reaction generates a thin, n-doped region in the absorber. We suggest that this aspect might be more important than the CdS layer in the formation of the junction. It is quite possible that the CdS/CuInSe2 device is a buried, shallow junction with a CdS window layer, rather than a heterojunction between CdS and CIGS. We use these ideas to develop methods for fabricating diodes without CdS or Cd.