Effect Of Wet Chemically Etching On Fabricating Process Of CdTe Solar Cells

In the present the study and application of thin film solar cells is the focus in the photovoltaic field. The poly crystalline thin films CdTe receive much attention as absorber materials for efficient, low-cost solar cells. The major problems met in the CdTe solar cell development have been the difficulty of forming of stable low resistance ohmic coniacts to p-CdTe。 To solve this issue, surface treatments are applied prior to deposition of metallic contact. In this article, the effects of nitric-phosphoric acid and bromine-methanol etching on properties of surfaces and device performance are investigated for polycrystalline CdTe-based solar cells.The major function of bromine-methanol etching is used to eliminate oxidation, other contamination and to smooth surface. A thin Te coating is demonstrated by XRD after enough time bromine-methanol etching. Dark IV measurement indicates that the roll-over of the IV cures is obvious and the reverse saturation current is very smaller by bromine-methanol etching. Cells pretreatment with bromine-methanol showed lower conversion efficiencies than these with nitric-phosphoric acid etch or without pretreatment.The nitric-phosphoric acid etched surface indicates that preferential etching occurs along the grain boundaries. The chemical etching leads to a roughening of thesurface because widened grain boundaries. The gas bubbles and a colour change of the surface can be observed in this etching process. This etching cleans the CdTe surface from oxides and other contamination, and creates a Te-rich layer mostly along the grain boundaries. The intensity of Te XRD reflection indicates that the content of Te in CdTe surface increases along with the etching time. Dark IV measurement indicates that the roll-over of the IV cures is weakly and the reverse saturation current is very larger by nitric-phosphoric acid etching. The average conversion efficiencies of cells by optimum nitric-phosphoric acid etching are little better than these without etching.Etching CdTe polycrystalline thin films deposited by Close-Spaced Sublimation shows that the devices performance by nitric-phosphoric acid etching is better than . by bromine-methanol etching. High-efficiency CdTe cell without etching is better than high-efficiency CdTe cell with nitric-phosphoric acid etching. The Schottky barrier is no avoided to form a good ohmic contact on p-type CdTe by wet chemically etching. Therefore, to improve back contact, CdTe surface pretreatment needs to be more investigated.