Rapid Cu(In,Ga)Se2 growth using "end point detection"

Thin film Cu(In,Ga)Se-2 (CIGS) is grown using a two stage co-evaporation process where all of the Cu is evaporated in the first stage. Near the end of the second stage, a Cu-rich to Cu-poor transition occurs, where the power delivered to the substrate heater in order to sustain a constant substrate temperature, changes as a result of a change in the radiative behavior of the CIGS film. The output power signal is shown to respond quickly to, and be characteristic of. the film composition near the transition. Using this signal to monitor the deposition process results in excellent control of the final Cu content, even when the evaporation rates are poorly known and poorly controlled. High quality devices result, even at high evaporation rates. Solar cells with efficiencies close to 15 % have been produced from CIGS deposition times below 15 minutes and are only marginally better for deposition times of up to 45 minutes, and this at constant substrate temperatures of 500 degreesC.