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

Recently, we demonstrated the positive effects of heat-light soaking (HLS) and subsequent heat-soaking (HS) on cesium fluoride (CsF) treated Cu(In-1-Ga-x,(x))Se-2(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-temperatureC-Vmeasurements. By optimizing the HLS and HS processes, CsF-treated CIGS solar cells yielded total efficiencies of over 20%.