n-type doping ofCuInSe2andCuGaSe2

Native point defects in CuIn1−xGaxSe2: hybrid density functional calculations predict the origin of p- and n-type conductivity

“…To simulate the experiments more closely, we calculate the total concentration of a defect -as a sum of the concentrations due to the different charge states -at 800 K. This is the temperature around which CIGS samples are usually grown, in coevaporation and in vacuum-based sequential growth methods, during selenization 43 . It is likely that the total concentration formed during growth freezes in during cooling down, due to kinetic barriers 10 . The ratios between the different charge states of the defects are subsequently calculated via the Boltzmann distribution at 300 K (the temperature at which the photovoltaic device is operated) and the concentrations per charge state redistributed accordingly.…”

“…In order to do this, we solve the self-consistent dependence, through charge neutrality, of the Fermi level and the defect concentrations that follow from the formation energies. This approach is rarely followed in other first-principles studies of defects, but in the case of CIGS it has also been attempted by C. Persson et al based on formation energies obtained within LDA 10 . Also, J. Pohl et al give a qualitative estimation of the Fermi level -namely the level where the formation energies of the dominant acceptor and donor are equal, but did not calculate the corresponding free charge carrier concentration 16 .…”

Thin-film ZnO/CdS/CuIn1-xGa xSe2 solar cells: anomalous physical properties of the CuIn1-xGa xSe2 absorber

“…The Cu-dSe-p hybridization forms an antibonding-like VB maximum which implies weak Cu-Se bonds. This is the origin to the low formation energy of Cu vacancies: ∆H f (V 0 Cu ) ∼ 0.8 + ∆µ Cu eV in CIS, and ∼ 0.6 + ∆µ Cu eV in CGS [5] and antisites: ∆H f (III 0 Cu ) ∼ 0.90 − ∆µ In + ∆µ Cu eV, and ∼ 2.43 − ∆µ Ga + ∆µ Cu eV [5]. Therefore, as-grown CIGS thin films are often extremely Cu-poor [1,2,8].…”

“…The ionization energies for Cd Cu is 0.05±0.05 eV in CIS and 0.12±0.06 eV in CGS, with relatively low formation energy, indicating that both CIS and CGS should be able to become ntype. (The error bar accounts multipole correction [5].) However, since CIGS has two different cation types (group-I and group III), the group II dopant will prefer to occupy the group III-site (creating II III acceptors) if the Fermi energy E F increase above mid-gap energy E g /2 (as in n-type materials) and thereby compensate the n-type character [5].…”

“…In this work, the electronic structure of bulk and reconstructed (112) surfaces of CIS and CGS are discussed from a theoretical perspective [3][4][5]. The impacts due to doping and surface reconstruction on the PV device performance are discussed.…”