How the Chlorine Treatment and the Stoichiometry Influences the Grain Boundary Passivation in Polycrystalline CdTe Thin Films

作者：Bosio Alessio; Rosa Greta^*; Menossi Daniele; Romeo Nicola

来源：Energies, 2016, 9(4): 254.

DOI：10.3390/en9040254

• cadmium telluride
• close-spaced sublimation
• chlorine treatment
• grain boundaries passivation

The absorption coefficient of CdTe is large enough to assure that all of the visible light is absorbed in a thickness on the order of 1 mu m. High efficiency devices are fabricated by using close-spaced sublimation (CSS)-deposited CdTe films with a thickness in the range of 6-8 mu m. In order to decrease the thickness of the CdTe film, a novel approach has been used. On top of the CdTe film, whose thickness is reduced to 2-3 mu m, another CdTe layer is deposited by RF sputtering, with a thickness of 100-200 nm. The purpose of this approach is to fill up the voids, which tend to form when a low thickness-CdTe film is deposited by close-spaced sublimation. Using this CdTe double layer, solar cells, with an efficiency greater than 15%, were reproducibly obtained. Since the CdTe layer deposited by the CSS technique shows a p-type behavior, whereas the layer deposited by sputtering is n-type, it is supposed that the formation of a p-n junction into the grain boundaries, which makes a mirror for the charge carriers, increases their mean lifetime. In order to also have this system after the essential chlorine treatment of the CdTe layer, a special cadmium-free halogen treatment was developed. This process was especially tuned for very thin (<= 3 mu m) CdTe film thickness and for not making use of cadmium-based chlorine salt while, producing high efficiency devices, meets a better economic and environmental sustainability.

• 出版日期2016-4