The Fox and the Hound - Na Doping and Ga Gradients in CIGS

Cu(In,Ga)Se2 (CIGS) thin film solar cells require appropriate Na doping and Ga concentration depth gradients to attain world record photovoltaic energy conversion. Na is known to hinder In/Ga interdiffusion in polycrystalline CIGS films, so these two strategies are interdependent. Firstly, this paper provides a review of Na doping and Ga depth gradients in CIGS, focusing on the currently accepted fact that Na hampers Ga diffusion. Secondly, such a view is challenged by newly published findings [1] showing that Na enhances In/Ga interdiffusion in monocrystalline CIGS films