Formation process and photovoltaic properties of Cu(In,Ga)Se2 and (Ag,Cu)(In,Ga)Se2 on flexible stainless steel substrates formed at different selenization temperatures

Abstract

Cu(In,Ga)Se2 (CIGS) and (Ag,Cu)(In,Ga)Se2 (ACIGS) films were successfully fabricated on stainless steel substrates using the non-vacuum spin-coating process followed by the selenization process. As the selenization temperature was increased to 550 °C, the Voc, Jsc, FF, and conversion efficiency of both CIGS and ACIGS solar cells were enhanced. On selenization at temperature above 550 °C, the morphology of the CIGS films become angular shape, and porous microstructures were formed. EDS and SIMS analyses revealed that the iron ions were substantially diffused from stainless steel substrates into the CIGS absorber layers. The existence of iron ions in CIGS thin films resulted in formation of short circuits of CIGS solar cells, thereby dropping the conversion efficiency of solar cells to zero. On the other hand, the efficiency of ACIGS was higher than that of CIGS solar cells owing to the high band gap and densified thin films. In addition, adding silver ions to the absorber layers effectively enhanced the stability of ACIGS thin films during high-temperature selenization, and suppressed the interaction between the absorber layers and iron ions. This research reveals that the incorporation of silver ions to form ACIGS improved the conversion efficiency at low selenization temperatures, and enhanced the stability of ACIGS films at high selenization temperatures.