Effect of High Monochromatic Radiation on the Electrical Performance of CIGS Solar Cell

In this article, we investigate the optically induced degradation of Cu(InGa)Se<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (CIGS) solar cells subjected to monochromatic laser irradiation. The devices under test are bifacial CIGS solar cells, fabricated on fluorine-doped SnO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> glass substrates. The electrical properties under dark and illumination conditions were characterized before laser exposure. The analysis of the current–voltage characteristics indicated that defect-assisted carrier transport dominates within the space charge region. Continuous laser exposure at constant optical power caused a decrease in open-circuit voltage (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub>). The study of the dark current–voltage curves highlights a change in the saturation current (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_S</i>) and ideality factor (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i>), whose increment follows a square-root dependence on time. This behavior is attributed to diffusion of Na ions toward the junction. Conversely, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> decay (which is correlated with the turn-<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> voltage decrease in dark <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I–V</i> curve) is ascribed to a light-induced defect generation that enhances leakage current at the CdS/CIGS interface.