Why clorine is an inefficient n-type dopant in cuinse2?

To unveil the physical origin of clorine (Cl) as the low effectiveness n-type dopant, the effects of Cl defects in CuInSe2 (CIS) with the different oping sites and defect-pairs are systematically investigated by first-principles calculations. The results exhibit that the Cl energetically prefers the nterstitial site instead of generally believed substitutional site with both Perdew-Burke-Ernzerhof (PBE) and Heyd-Scuseria-Ernzerhof (HSE06) unctionals. The electronic structure calculations further show that doping would be p-type when Cl occupies the interstitial site, which is greatly ifferent from the n-type doping in substitutional site. Such results clarify the intrinsic mechanism of the low effectiveness of n-type Cl-doping in IS.