Efficiency Improvement of Cu(InGa)Se_2 Thin Film Solar Cells with a High Ga Composition Using Rapid Thermal Annealing

摘要

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℃.