Control of an interfacial MoSe ₂ layer in Cu ₂ZnSnSe ₄ thin film solar cells: 8.9 power conversion efficiency with a TiN diffusion barrier

We have examined Cu 2ZnSnSe 4 (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 MoSe 2 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 MoSe 2 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. © 2012 American Institute of Physics.