“…According to these studies, a selenium vacancy (V Se ), interstitial copper (Cu i ), and an indium substituted at a copper site (In Cu ) behave as donors, whereas a copper vacancy (V Cu ), an indium vacancy (V In ), and a copper substituting an indium site (Cu In ) behave as acceptors in CuInSe 2 . Several electronic transitions among these defect levels, the conduction band (CB), and the valence band (VB) are observed as PL and cathode luminescence; − the observed emissions significantly depend on whether the chemical composition deviates from stoichiometric to a Cu-rich or In-rich composition. ,, For instance, the transitions from CB to V In and/or Cu In acceptors and from V Se and/or Cu i to VB are dominant for the Cu-rich composition; on the other hand, donor−acceptor pair (DAP) recombination, such as from V Se to V Cu and from In Cu to V Cu , are dominant for the In-rich composition.…”