Temperature-dependent current–voltage and admittance spectroscopy analysis on cesium-treated Cu (In_{1 − x},Ga_x)Se₂ solar cell before and after heat-light soaking and subsequent heat-soaking treatments

Recently, we demonstrated the positive effects of heat-light soaking (HLS) and subsequent heat-soaking (HS) on cesium fluoride (CsF) treated Cu(In₁-_x,Ga_x)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%.