The intra-absorber junction (IAJ) model for the device physics of copper indium selenide-based photovoltaics

The results of free-energy computational materials modeling (CMM) of the CIS ternary material system are applied to analysis of the processes of charge separation fundamental to the operation of all PV devices. It is known that all high-efficiency devices with CIS absorbers possess indium-rich compositions, which lie in the two-phase α+β domain of the equilibrium CIS phase diagram. The intra-absorber junction (IAJ) model presented here explores the implications of presuming that CIS absorbers are in fact two-phase mixtures and concludes that this heterogeneity is fundamental to charge separation in devices made from them. The model posits that photo-generated carrier pairs are first separated within the absorber, the holes into the α and electrons into the β-phase, respectively. These two phases segregate on a nanometer length scale to form an interpenetrating multiply-connected network which permits percolation transport of both excess carrier populations in physically distinct paths. Thus recombination of the hole and electron photocurrents within the absorber is reduced by their real-space separation.