Comparison of Nickel Sulphide (NiS) Thin Films for Photovoltaic Applications Prepared by Different Methods

Nickel sulphide (Ni–Sₓ) thin films are increasingly seen as promising multifunctional materials due to their phase-dependent electrical conductivity, adjustable band gap, excellent electrochemical activity, and catalytic abilities. The Ni–S system exhibits diverse polymorphs, including NiS, NiS₂, Ni₃S₂, and other non-stoichiometric phases, enabling applications in photovoltaics, supercapacitors, lithium-ion batteries, hydrogen evolution catalysis, sensors, and optoelectronics. This chapter offers a thorough review of synthesis methods, structural characterisation techniques (XRD, SEM, TEM), optical band gap measurement via Tauc analysis, electronic band structure considerations, and a comparison of chemical bath deposition (CBD) and physical vapour deposition (PVD) processes. It also explores challenges related to phase control, defect engineering, and stability, along with future prospects in flexible electronics and hybrid heterostructures.