Impact of the Ga/In ratio on defects in Cu(In, Ga)Se2

The impact of the composition of a 3-stage-process deposited CIGS on the deep level spectrum was investigated using deep level transient and optical spectroscopies to probe defects throughout the bandgap to have a complete picture of the defect spectrum. It is shown that the defect spectra depend strongly on the Ga/In ratio with both higher numbers of trap levels and higher trap concentrations (by >65%) on average in the higher Ga content films. These facts can likely explain the reduced CIGS solar cell efficiency at higher Ga content.