CIGS solar cells grown by a three-stage process with different evaporation rates

Solar cells based on polycrystalline Cu(In,Ga)Se₂ (CIGS) absorber layers have shown high potential for low cost photovoltaic energy conversion. Our group has achieved 18.1% efficient cells on glass substrates and 14.1% on flexible polyimide foils without antireflection (AR) coating. These results were achieved by applying a three-stage evaporation process with common growth rates of about 35 nm/min. Aim of this study was to enhance the growth rates of layers deposited at low substrate temperature (450°C) suitable for polyimide foils and to investigate structural properties of CIGS layers and photovoltaic properties of solar cells. It was found that very high deposition rates of 500 nm/min during the 2nd and 3rd stage of the evaporation process are feasible, maintaining high absorber quality and performance of solar cells.