Influence of selenization temperatures on the microstructures and photoelectric properties of iron-ion doped Cu(In,Ga)Se2 thin-film solar cells

Cu(In,Ga)Se2 (CIGS) thin films were prepared on molybdenum-coated flexible stainless steel substrates through a non-vacuumspin-coating process followed by selenization at temperatures ranging from 450 °C to 575 °C. The effects of selenization temperatures and concentration of iron ions on the photoelectric properties of the CIGS solar cells was thoroughly investigated. All X-ray diffraction (XRD) patterns appropriately matched with those of CIGS phase. The diffraction peak intensities of undoped CIGS films were increased with an increase in selenization temperatures. However, XRD peak intensities of iron-ion doped CIGS films were decreased with the elevation of selenization temperatures owing to the degradation of thermal stability of CIGS films after iron-ion doping. As the selenization temperatures increased, the grain sizes of particles in CIGS films increased, and the films became densified with flat surfaces. The values of Voc, Jsc, and fill factor for CIGS solar cells prepared at 450 °C were 0.401 V, 21.84 mA/cm2, and 41.12%, respectively. These parameters were enhanced with increasing selenization temperatures due to improved crystallinity of CIGS and densified microstructures. However, iron-ion doping deteriorated the photoelectric properties because iron ions diffused into the absorption layers at high temperatures. The present study indicates that iron-ion doping adversely affected the photoelectric performance and microstructures of CIGS solar cells.