Single Step Electrochemical Deposition of p-Type Undoped and Co²⁺Doped FeS₂Thin Films and Performance in Heterojunction Solid Solar Cells

Undoped and Co 2+ doped FeS 2 thin films (Co compositions are 1 to 5 mole%) were deposited on indium tin oxide glass substrate by a single step electrochemical deposition (ECD) method at low temperature (70 °C). Glancing angle X-ray diffraction (GAXRD) and Raman spectra showed that as-deposited undoped and Co 2+ doped FeS 2 thin films have a cubic pyrite structure without any trace of orthorhombic marcasite phase. Co 2+ doping does not affect the cubic structure of FeS 2 thin films with a strong (111) plane preferred orientation in all the doped thin films. The height profiling of 3 mole% of Co 2+ doped FeS 2 thin film by atomic force microscopy revealed a smooth surface with uniform distribution of particles and low roughness values. Co 2+ (3, 4 and 5 mole%) doped thin films show a strong absorption peak in the higher wavelength region. Magnetic measurement reveals that Co 2+ doping into the FeS 2 lattice induces ferromagnetism. The Co 2+ in FeS 2 thin films acts as the acceptor and the original p-type conductivity is retained. Solar light irradiation with the intensity of 100 mW/cm 2 on Co 2+ (3 mole%) doped FeS 2 thin film cell resulted in a power conversion efficiency of 5.42%.