Thin film iron pyrite deposited by hybrid sputtering/co-evaporation as a hole transport layer for sputtered CdS/CdTe solar cells

We report the properties of hybrid deposited iron pyrite (FeS2) thin films applied as the back contact interface layers of CdS/CdTe solar cells. The hybrid deposition process for FeS2 optimized in this study relies on DC magnetron sputtering of iron with simultaneous thermal evaporation of sulfur. We have fabricated solar cells incorporating CdS/CdTe window/absorber layers sputter-deposited onto commercial transparent conducting oxide coated glass and have compared the performance of devices incorporating the new FeS2/Cu/Au back contacts with that of standard devices incorporating Cu/Au back contacts. Cdnsidering our best devices of each type, the inclusion of the FeS2 thin film as a hole transport layer has improved the open circuit voltage V-oc by 2.1%, reaching 817 mV, and the fill-factor FF by 8.3% relative, reaching 74.7%, in comparison with devices omitting the FeS2 layer. Under standard test conditions of 100 mA/cm(2) simulated AM1.5G and 25 degrees C, devices utilizing the FeS2 hole transport layer have shown a conversion efficiency eta as high as 13.3% - a relative increase in eta of similar to 10% over our current laboratory standard back contact. The attained FF exceeds previous results for high efficiency sputter-deposited CdS/CdTe solar cells.