Interplay of Polymorphism in FeS₂ Thin Films by Phosphorus Doping

Achieving p-type pyrite FeS2 is essential for its effective use in thin film photovoltaics. Phosphorus (P) is emerging as a prominent anionic dopant in pyrite to induce p-type electrical conductivity. This study investigates the impact of P doping on the structural and electrical characteristics of pyrite thin films. Films are fabricated using DC magnetron sputtering, initially yielding sulfur (S)-poor FeS2–x phase. Annealing in S atmosphere yields phase-pure pyrite, while coannealing with higher P introduces mixed pyrite-marcasite phase p-type conductivity. An Increasing of band gap from 1.08 to 1.43 eV is also observed, with high hole mobility of 150.62 cm2 V–1 s–1. P integration in FeS2 is confirmed by X-ray photoelectron spectroscopy (XPS) via P–S and Fe–P binding energies. The mixed pyrite-marcasite phase is confirmed by Raman results. This mixed phase p-type FeS2 can help increase the photovoltaic performance. However, it also shows excessive doping causing nonuniformity and contact behavior.