CdTe solar cells: Nucleation, structure, and performance

CdTe solar cells are strongly influenced in their performance by the morphology of the absorber layer. Therefore, we have systematically investigated CdTe film formation deposited by close space sublimation. At low sample temperature the films tend to form compact layers with preferred (111) orientation which is lost at elevated temperatures above 420°C. For CdS layers without (0001) texture there is in addition a low temperature regime (350°C) with (111) texture loss. Within this temperature regime we have found a large concentration of plane defects related to a hexagonal CdTe layer sequence. After activation treatment the (111) texture is lost for all deposited layers leading to strong recrystallisation of the grains and to rough surfaces and the tendency of pin-hole formation. This effect is minimized for the 350°C deposited layers. As a consequence we have observed maxima in the conversion efficiencies for this temperature in addition to the high temperature regime.