Precise Se-flux control and its effect on Cu(In,Ga)Se2 absorber layer deposited at low substrate temperature by multi stage co-evaporation

In-situ Se flux control system is applied for the growth of Cu(In,Ga)Se2 (CIGS) absorber layers by a multi stage thermal co-deposition of elements at low substrate temperature below 500 °C. It was revealed that the composition depth profile of the [Ga]/([In]+[Ga]) (GGI) ratio is affected by the [Se]/[Metal] flux ratio. It was observed for the solar cell properties that the change in the depth profiles of GGI induced by the change of [Se]/[Metal] resulted in an increase in the JSC and a decrease in the FF, and hence little influence on the efficiency. Under control of [Se]/[Metal] ratio during the deposition process, the effect of CIGS layer thickness on the solar cell properties was investigated. With increase in the thickness up to 2.8 μm, the short circuit current density was increased to over 35 mA/cm2 w/o AR coating, resulting in conversion efficiency above 18% using low temperature deposition method.