Temperature‐dependent current–voltage and admittance spectroscopy analysis on cesium‐treated Cu (In1 − x,Gax)Se2 solar cell before and after heat‐light soaking and subsequent heat‐soaking treatments

Abstract

AbstractRecently, we demonstrated the positive effects of heat‐light soaking (HLS) and subsequent heat‐soaking (HS) on cesium fluoride (CsF) treated Cu(In1‐x,Gax)Se2 (CIGS) solar cells. However, the role of defects formation and its influence on the electronic properties have not been analyzed. With this motivation, here, we analyzed the electronic properties of CsF‐free and CsF‐treated CIGS solar cells before and after HLS and subsequent HS treatments using temperature‐dependent current–voltage (J–V–T), admittance and low‐temperature capacitance–voltage (C–V) measurements. We noticed that CsF‐treated CIGS solar cells form a minority carrier trap level after HLS. The subsequent HS treatment was found to be beneficial to compensate this defect level. The admittance measurement showed a shift of the shallow energy position to a higher value after HLS and subsequent HS treatments, irrespective of Cs incorporation. This is expected to be due to the formation of a secondary diode toward the CIGS/molybdenum contact. The positive and negative effects of HLS and subsequent HS treatments on CsF‐treated CIGS solar cell are discussed using low‐temperature C–V measurements. By optimizing the HLS and HS processes, CsF‐treated CIGS solar cells yielded total efficiencies of over 20%.