Impact of air‐light exposure on the electrical properties of Cu(In,Ga)Se 2 solar cells

The impact of air‐light exposure of bare Cu(In,Ga)Se 2 layers is investigated by measuring the performance of completed solar cells. Solar cells formed from air‐light–exposed absorbers reveal inferior cell parameters by about 10% regarding open circuit voltage, fill factor, and efficiency compared with cells from nonilluminated absorbers. Time‐dependent and temperature‐dependent open circuit voltage measurements give reasons that the solar cell impairment by air‐light exposure of the bare absorbers is due to interface recombination. Interface states are detected by admittance spectroscopy. Heat‐light soaking of complete solar cells—having formerly degraded interfaces—recovers the solar cell parameters up to the nondegraded levels. Paradoxically, both the air‐light–induced degradation of bare absorbers and the revision of cell parameters after light annealing go along with a light‐induced segregation of sodium at the Cu(In,Ga)Se 2 surface and Cu(In,Ga)Se 2 /CdS interface, respectively.