Effect of Window-Layer Materials on p-n Junction Location in Cu(In,Ga)Se2 Solar Cells

We report on measurements of junction location in Cu(In,Ga)Se-2 (CIGS) solar cells with different window-layer materials by nm-resolution electrical potential/field profiling across the junction using Kelvin probe force microscopy imaging on cross-section of the devices. The results illustrate that the device with a CdS window layer (CdS/CIGS) has a buried homojunction located inside the CIGS absorber with similar to 40-nm junction depth, whereas the ZnOS/CIGS devices with and without partial electrolyte treatment prior to the window-layer deposition are similar, exhibiting a heterointerface junction. This junction location may contribute in part to the highest efficiency of the CdS/CIGS device among the three devices.