Effect of an additional Cu-deficient layer deposition on alkali treated Cu(In, Ga)Se2 solar cells deposited at low temperature

In this work, we found that the deposition of a Cu-deficient layer after alkali post-deposition treatment (PDT) of Cu(In,Ga)Se-2 (CIGS) at low temperature (450 degrees C) effectively improves the performance of CIGS solar cells. Compared to the CGIS with only the alkali PDT, the deposition of the Cu-deficient layer leads to the formation of larger holes on the surface and results in higher efficiency. The conversion efficiency improved from 11% to 16% after alkali PDT and Cu-deficient layer deposition because of a passivation effect. The formation of a passivation layer after both alkali treatment and Cu-deficient layer deposition was observed by TEM-EDX, showing that the deposition of the Cu-deficient layer could contribute to a low Cu surface composition. Finally, the effect on the CIGS and CdS interface was analyzed using electron-beam-induced current measurement (EBIC).