Enhanced Optical Properties of FeS2 Using Ni@Cu Doping and Characterization of the Structural and Chemical Compositions for Solar Cell Applications

Transition metals doped FeS2 thin films are promising materials for optoelectronics, energy saving and storage applications. This is a first time report on the simultaneously Ni@Cu doped Fe1 – xMxS2 (M = Ni@Cu = 0, 2, 5, 10, and 20 at %) thin films fabricated by a simple chemical spray pyrolysis technique. In this paper we investigate the impact of doping on the structural, chemical states, optical properties and band gap nature by different characterization techniques. The SEM results show that surface morphology and granular grain size changes with the increment of Ni@Cu content which are coherent with the XRD results. The EDX and XPS measurements exhibit that the films are composed of Fe, S, Ni, and Cu elements whilst the films were slightly oxidized due to processing in the atmospheric conditions. Spectroscopy ellipsometry (SE) analysis demonstrates that the indirect band gap gradually increased from 1.38 eV (FeS2) to 1.64 eV (Ni@Cu = 10 at %) while at higher doping the band gap was decreased to 1.53 could be due to incomplete doping. So, the band gap of FeS2 can be tuned in between 1.38 and 1.64 eV by simultaneous Ni@Cu doping could be a suitable candidate for absorber application in solar cell devices. The other optical constants (dielectric constants, refractive index and extinction coefficient) explicitly carried out using SE measurement. Interestingly, progressing the absorption nature and bang gap in the visible region disclose a significant impact on the optical properties for optoelectronics applications.