Significant enhancement of thermoelectric power factor in Ni-Doped FeSe thin films via defect and carrier engineering

In this study, the thermoelectric power factor of Ni-doped FeSe films were thoroughly investigated. The pure FeSe and Ni-doped FeSe with doping concentrations of 1%, 2%, 3%, and 5%, were synthesized using the thermal evaporation route. X-ray diffraction has confirmed the formation of crystalline FeSe phase with the peaks corresponding to the (101), (110), (200), and (202) planes. The diffraction peaks were shifted towards higher angles with increasing the Ni content indicates lattice contraction due to successful incorporation of nickel into the FeSe lattice. Scanning electron microscopy has revealed the variation in surface morphology with nickel doping content including grain refinement and increased grain boundary density. The 3% Ni-doped film exhibited dense and uniform microstructure with fine grains, while the 5% doping led to structural degradation. The prepared samples have exhibited negative Seebeck coefficients, confirming n-type conduction. The pure FeSe film showed Seebeck coefficient of −120 µV/K at 300 K, which increased in magnitude with temperature. The Seebeck value has decreased with the nickel doping concentration, due to increased carrier conctent, while electrical conductivity improved significantly. The 3% Ni-doped FeSe film demonstrated the best thermoelectric power factor, with Seebeck value of −85 µV/K and conductivity value of 580 S/cm at 300 K. The maximum power factor has reached 15.67 µW/cm·K 2 at 550 K. Hall measurements have measured, increase in carrier concentration from 1.5 × 10 18 cm -3 of pristine FeSe film to 8.5 × 10 18 cm -3 of 3% Ni doped FeSe film accompanied via decrease in mobility due to enhanced scattering. The significant improved thermoelectric power factor of Ni-doped FeSe thin films is attributed to the optimized balance between carrier concentration, mobility, and microstructural features. The results confirmations that 3% Ni doping is the optimal composition for enhancing thermoelectric efficiency.