Photovoltaic Properties of Homojunction CIGS Solar Cells Using Various Divalent N-Type Dopants

28th European Photovoltaic Solar Energy Conference and Exhibition; 2299-2301
In order to investigate important factors required of N-type dopants for CIGS, various divalent ions, namely Mg, Ca, Mn Fe, Co, Ni, Cu, Zn and Cd, were doped as N-type dopants in CIGS thin films with the liquidphase doping method and homojunction cells were fabricated. A maximum conversion efficiency of 17.7% was obtained for Cd-doped homojunction cell but no photocurrents were observed for Co-, Ni- and Cu-doped cells. Comparison with conversion efficiency and formal valence (V; estimated by bond valence sum calculation, BVS) revealed that conversion efficiency depends on formal valence and shows a peak at V = +3. Ions applied in a highefficiency cell seem to act as an effective N-type dopant. The above results indicate that the important factors required of N-type dopants are the electronic configuration of the outermost electron shell and the coordination environment determining the formal valence.