Cu(In,Ga)Se2 thin-film evolution during growth - a photoluminescence study

An in-depth understanding of the defect formation and resulting changes in material quality occurring during the Cu(In,Ga)Se₂ growth process is vital to the successful and widespread use of this photovoltaic material. In an attempt to develop such an understanding, we investigated the growth of Cu(In,Ga)Se₂ thin films from (In,Ga)₂Se₃ precursors. This was achieved by using energy- and time-resolved photoluminescence spectroscopies to characterize a series of thin films, each removed at a different point along the reaction pathway of the "three-stage" growth process. The resulting thin films are representative of the absorber layer as it proceeds from a Cu-rich to Cu-poor state. The experimental results support a growth model incorporating changes in the dominant defect states and improvement in the recombination lifetime during this final stage of the growth process as the material transitions to a Cu-poor phase.