Characterization and modeling of reverse-bias breakdown in Cu(In,Ga)Se2 photovoltaic devices

Partial shading of series-connected thin-film photovoltaic modules can force shaded cells into reverse bias, which can cause rapid and irreversible power loss and reduce the practical module lifespan. Unfortunately, this is a common occurrence in field-deployed modules due to the myriad of environmental factors that can result in partial shading. In this work, we identify as-grown nonuniformities in the Cu(In,Ga)Se-2 (CIGS) absorber layers as the points of origin for the damage induced under reverse-bias conditions. The structure and chemistry associated with inclusions and voids in the CIGS films cause these features to act as resistive heating elements in reverse-bias conditions. This localized resistive heating provides the energy required to induce thermal runaway breakdown in the CIGS devices, resulting in damage to charge collection and reduced active area of a device. This mechanism is also described with a robust device model to connect the experimental observations with their physical origins.