Impact of CdS annealing atmosphere on the performance of CdS–CdTe solar cell

•Annealed CdS films are used for CdTe based solar cells.•CdS–CdTe solar cell with air annealed CdS shows better performance.•The air annealed CdS brings the O2 and chloride at the place of junction formation.•H2 removes the oxygen containing compounds from CdS grain boundaries. CdS thin films obtained by chemical bath deposition and annealed in hydrogen and air ambients were combined with CdTe absorbers obtained by close spaced sublimation. CdS–CdTe solar cells in superstrate configuration were characterized by current–voltage and quantum efficiency measurements while the analysis of annealed CdS films was made by scanning electron microscopy, X-ray diffraction and UV–vis spectroscopy. It was found that in superstrate configuration, due to the big grains on CdS surface and gas emission from CdS film at high temperature deposition of the absorber, the delamination of layers take place. Annealing in H2 removes the oxygen compounds from CdS grain boundaries and opens them for formation of shortcutting through the CdS layer. The processing in air is most advantageous due to simultaneous presence of chloride and oxygen, contributing to the recrystallization and sintering of the highly textured columnar CdS. The direct influence of the CdS annealing on the solar cell parameters is shown for CdS–CdTe solar cell.