CdTe solar cells employing CdS1−yTey window layers

Oxygenated cadmium sulfide (CdS:O) is an alternative CdTe window layer that delivers improved blue response relative to CdS. Our recent study revealed that CdS: O completely transforms during device fabrication into a layer containing cadmium sulfate clusters interspersed among CdS
_1-y
Te
_y
nanocrystals. This motivated us to study CdTe solar cells employing pre-formed CdS
_1-y
Te
_y
alloy windows without sulfate present. The intrinsic properties of alloys deposited by co-evaporation are evaluated and then used in place of CdS in standard device fabrication. Interestingly we find that device efficiency is nominally unchanged, but there are significant tradeoffs between current collection, fill factor, and open circuit voltage with alloy composition. XRD analysis of interdiffusion with CdTe is performed and the results show that it is largely suppressed in alloy-based devices.