Investigation of CdZnS Buffer Layers on the Performance of CuInGaSe2 and CuGaSe2 Solar Cells

Cu(In,Ga)Se₂ (CIGS) and CuGaSe₂ (CGS) solar cells were fabricated using Cd_1-xZn_xS (CdZnS) buffer layers prepared by chemical bath deposition (CBD) with relative Zn compositions in the CBD bath values of X_bath=0 (i.e., pure CdS), 0.1, 0.2, 0.3, 0.4, and 0.5. The cell performance parameters of CIGS and CGS films treated with a KCN solution were investigated and compared to cells without KCN treatment. It was found that absorber films treated with KCN etching prior to the buffer CBD step show an improved cell performance for both the CIGS and CGS cells deposited with either CdS or CdZnS buffer layer. A CIGS cell with CdZnS buffer layer of X_bath=0.2 produced a 13% AM1.5G conversion efficiency with higher V_oc, J_sc, and FF values as compared to the CdZnS/CIGS cells with different Zn contents. Results of photo- J-V and quantum efficiency (QE) measurements reveal that the CGS cell with CdZnS buffer layer of X_bath=0.3 performed better than the CGS cell deposited with a pure CdS buffer layer. This result is suggested as a result of an increased photocurrent at shorter wavelengths and a more favorable conduction band-offset at the CdZnS/CGS junction