Facile Phase Control of Solution-Processed Copper Iron Sulfide Nanocrystals for a Low-Cost Self-Powered NIR Photodetector with Fast Response

Phase control of nanomaterials, determined by thermodynamic or kinetic conditions, is essential to sulfides’ characteristics, offering opportunities for exploring advanced applications in the field of optoelectronics. However, the one-step, high-yield, and defect-free synthesis of phase-pure nanoscale sulfides remains challenging. In this work, the low-cost solvothermal process enabled precise regulation of the phase evolution process to synthesize the expected sulfide (three phases in the Cu–Fe–S system) nanocrystals in a phase-pure form at low temperatures. These nanocrystals exhibited broadband photoabsorption ranging from the visible to the near-infrared (NIR) region. Subsequently, a solution-processed uniform CuFeS2 nanocrystal film was deposited on CdS by the same one-step route to create the first CuFeS2-based self-powered NIR photodetector. These devices demonstrated a superior stable and reproducible detection performance without bias voltage under NIR illumination, even up to 1050 nm, resulting from their suitable size. The rapid rise and decay times of ∼38 and ∼49 ms indicated that the devices are capable of high-frequency switching detection. Moreover, detailed chemical processes through accurately tuning the oxidation states, the influence of CuFeS2 nanoparticle size, phase control, and film thickness on performance were proposed in detail.