Influence of Ga-notch position on recombination processes in Cu(In,Ga)Se2-based solar cells investigated by means of photoluminescence

One of the consequences of the deposition of Cu(In,Ga)Se2 (CIGSe) absorber by a three stage process is a non-uniform Ga distribution. It takes the form of the so-called Ga-notch and is considered to be crucial for achieving highly efficient CIGSe solar cells. However, the influence of this sequential element co-evaporation on defect related properties of the absorber is not fully understood. In this paper, we use voltage dependent photoluminescence (PLV) to investigate the impact of a different Ga-notch position on recombination processes in CIGSe-based solar cells. The most striking difference between investigated samples is the increased sensitivity of the photoluminescence signal to blue light, as the position of the Ga-notch moves away from the CdS/CIGSe interface. Such metastable behavior of PLV characteristics and its close correlation with changes observed in capacitance–voltage curves suggest an increased concentration of deep defects in the top CIGSe layer. We propose that the observed changes of PLV characteristics can be explained by electrical field redistribution within the junction due to charging of deep metastable defects.

► The influence of Ga-notch position on cell performance was investigated.
► Voltage dependent photoluminescence (PLV) was used as a tool.
► Sensitivity of the PLV to blue light is observed when Ga-notch is deeper in absorber.
► Metastable behavior of PLV suggests the increased concentration of deep defects.
► Modification of Ga-notch position may lead to deterioration of absorber quality.