STABILITY OF CU(IN,GA)SE-2 SOLAR-CELLS AND EVALUATION BY C-V CHARACTERISTICS

To confirm the long-term reliability of Cu(In,Ga)Se-2 (CIGS) solar cel ls, we investigated the I-V and C-V characteristics during rests under irradiation or dark condition. Under irradiation, the test samples sh owed a little increase in efficiency (eta) and open-circuit voltage (T -oc) which showed their electrical durability to light irradiation. Bu t the diode factor (n) and series resistance (R-s) showed large change s in value. Also, the built-in voltage (V-b) and density gradient (dN( A)/d(X)) in the CIGS layer calculated from the C-V characteristics sho wed distinct changes during the test. After Lt SUN irradiation, two sa mples in the same fabrication-lot showed new light absorption in the l ower-energy range than sun the energy gap of CIGS. We explain the chan ge of C-V characteristics for the samples under strong irradiation wit h a new model named ''Junction retrograde'' which can treat defect gen eration by irradiation to reduce the acceptor density in graded pn jun ction. This model for C-V analysis can be used to investigate the long -term reliability of CIGS solar cells under irradiation.