Spray-ILGAR ZnS nanodots/In2S3 as defect passivation/point contact bilayer buffer for Cu(In,Ga)(S,Se)2 solar cells

The sequential and cyclic spray ion layer gas reaction (spray-ILGAR) technique allows the deposition of metal chalcogenide films controllable from monodispersed nanodots to homogeneous compact layer. With access to this technique, a structured buffer layer for Cu(In,Ga)(S,Se)2 cells, named “defect passivation/point contact bilayer buffer” is introduced at the heterogeneous interfaces to replace the conventional toxic CdS buffeProd. Type: FTPr material and to improve the pure In2S3 buffer. Here, the spray-ILGAR ZnS nanodots serve as a passivation layer with a reduced interface recombination, while the compact spray-ILGAR In2S3 film on top and in-between the nanodots acts as point contact layer for the charge carrier transport. The optimal ZnS dot density and In2S3 thickness are determined and discussed in detail. As yet, the solar cell efficiency with ZnS/In2S3 buffer layer can be improved by about 1.5% absolutely as compared to a pure In2S3 buffered cell. Apart from the electronic properties of the absorber/buffer interface, also the chemical and diffusion processes during junction formation, which may influence the properties of the completed solar cell, are investigated and discussed.