Limitation of the open-circuit voltage due to metastable intrinsic defects in Cu(In,Ga)Se2 and strategies to avoid these defects

Using first-principles defect theory, we investigate the role of intrinsic point defects in the limitation of the opencircuit voltage (VOC) in Cu(In,Ga)Se2 solar cells. We find that the intrinsic donors InCu (In-on-Cu antisite defect) and VSe (Selenium vacancy) and their defect complexes with VCu (Cu vacancies) represent two independent mechanisms that are expected to cause saturation of VOC around 1 eV, when the absorber band gap is increased towards Ga-rich compositions. Strategies to avoid these sources of VOC limitation are discussed.