We report the application of thin film nanocrystalline (NC) FeS2 as the copper-free back contact for CdTe solar cells. The FeS2-NC layer is prepared from solution directly on the CdTe surface using drop-casting coupled with a hydrazine treatment at ambient temperature and pressure, and requires no thermal treatment. Copper-free solar cells based on the CdS/CdTe/FeS2-NC/Au architecture exhibit device efficiencies > 90% that of a standard Cu/Au back contact devices. The FeS2-NC back contact solar cells show good thermal stability under initial tests. Devices prepared with untreated FeS2-NC back contacts display a strong "S-kink" behavior which we correlate with a high hole-transport barrier arising from inter-NC organic surfactant molecules. (C) 2015 Elsevier B.V. All rights reserved.