Control of an interfacial MoSe2 layer in Cu2ZnSnSe4 thin film solar cells: 8.9% power conversion efficiency with a TiN diffusion barrier

We have examined Cu2ZnSnSe4 (CZTSe) solar cells prepared by thermal co-evaporation on Mo-coated glass substrates followed by post-deposition annealing under Se ambient. We show that the control of an interfacial MoSe2 layer thickness and the introduction of an adequate Se partial pressure (P-Se) during annealing are essential to achieve high efficiency CZTSe solar cells-a reverse correlation between device performance and MoSe2 thickness is observed, and insufficient P-Se leads to the formation of defects within the bandgap as revealed by photoluminescence measurements. Using a TiN diffusion barrier, we demonstrate 8.9% efficiency CZTSe devices with a long lifetime of photo-generated carriers. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4740276]