Close-space sublimation grown CdS window layers for CdS/CdTe thin-film solar cells

We report on the synthesis and characterization of CdS window layers grown by close-space sublimation (CSS) method for CdS/CdTe thin-film solar cells. Comparing with CdS window layers grown by other methods such as sputtering and chemical bath deposition, CSS-grown CdS layers can facilitate the consumption of CdS layers and suppress the diffusion of Te into CdS window layers. CSS-grown CdS layers exhibit much larger grains with faceted morphology. Due to large grains, CSS CdS layers must be grown thick enough to minimize the effects of pin-holes. The use of thicker CdS layer causes reduced blue response, resulting in current loss. Therefore, the thickness of CSS CdS window layer must be carefully optimized to achieve high efficiency. Our best small area dot cell using a CSS CdS window layer has exhibited a cell efficiency of about 14.2 % with an open circuit voltage (V_OC) of 806 mV, a short circuit current (J_SC) of 25.2 mA/cm², and a fill factor (FF) of 69.8 % under AM1.5 illumination and without an antireflection coating, slightly lower than our best reference cell using a sputtered CdS window layer (V_OC = 845 mV, J_SC = 24.5 mA/cm², FF = 76.8 %, and efficiency = 15.8 %).