Efficiency Improvement of Cu(InGa)Se 2 Thin Film Solar Cells with a High Ga Composition Using Rapid Thermal Annealing

Cu(InGa)Se 2 (CIGS) thin films were grown by three-stage growth process using a molecular beam deposition system on a Mo/soda lime glass (SLG) substrate. The raman scattering spectroscopy of as-grown samples with a high Ga composition showed the presence of Cu 2- x Se compounds, which are thought to be responsible for the degradation of the open circuit voltage of solar cells. Rapid thermal annealing (RTA) using an infrared lamp in forming gas (N 2 95% + H 2 5%) ambient under atmospheric pressure was examined in order to remove the Cu 2- x Se compounds, and it was found that hydrogen is necessary to remove the Cu 2- x Se compounds. The influence of RTA conditions on device performance was investigated. A Cu(In 0.4 Ga 0.6 )Se 2 (energy band gap: E g =1.37 eV) solar cell with an efficiency of 11.7%, particularly open circuit voltage ( V oc ) increased from 640 to 750 mV, was obtained by RTA at 400°C.