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)Se₂ (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.