Study of the electronic properties of wide band gap CIGSe solar cells: Influence of copper off-stoichiometry

International audienceThe objective of this work is to study the influence of the copper (Cu) content (y = [Cu]/([In] + [Ga])) on the electronic properties of wide band gap (1.35 eV, x = [Ga]/([In] + [Ga]) ~ 0.55) Cu(In,Ga)Se2 (CIGSe) thin film solar cells. For this study, solar cells samples with a variation in y from 0.97 to 0.84 have been fabricated. The efficiencies of solar cells have been divided by two for y varying from 0.97 to 0.84. Junction capacitance methods and photoluminescence were used to get information about space charge and defects properties. The increase of the Cu-content y of the absorber, leads to a widening of the space region, due a decrease of the net carriers concentration. The photoluminescence spectra of the solar cells with high absorber Cu-content y, slightly close to stoichiometry 0.95-0.97) have revealed a defect level of about 0.18 eV, which is not present in the solar cells with y less than 0.95. These observations are discussed in terms of a decrease of the defect complex (2VCu + MCu with M = In or Ga) stability at higher Ga contents