Pioneering method for the synthesis of lead sulfide (PbS) nanoparticles using a surfactant-free microemulsion scheme

In this study, we report the synthesis of PbS particles having dimensions in the quantum-dot regime (13.17 to 26.91 nm) using a cyclohexane:isopropanol:dimethyl-sulfoxide surfactant-free microemulsion (CID-SFME) scheme without a capping agent. We found that with an increase in the microemulsion concentration and particle size, there was a simultaneous reduction in band gap due to the quantum confinement effect. Furthermore, a microemulsion concentration of 0.0125 M was the optimum microemulsion concentration for the growth of uniformly distributed, small particle-sized, ordered PbS nanoparticles using CID-SFME at a constant temperature and other effective parameters. From the results obtained in the present study, we believe that during the reaction, it was not the low values of viscosity and dielectric constant that were responsible for keeping PbS stabilized inside the core of the micelle of the CID microemulsion, but rather the van der Waals forces that also controlled the growth of spherical PbS. We fabricated a highly stable FTO/TiO₂/PbS/PANI/NiS/C photodetector at an optimized microemulsion solution concentration. The fabricated photodetector showed a rise time of ∼0.39 s and a decay time of ∼0.22 s, with a photoresponsivity of ∼5.466 μA W^-1, external quantum efficiency of ∼0.116 × 10^-4%, and detectivity of 6.83 × 10⁷ Jones. Therefore, the CID-SFME scheme is an easy, low-cost route to fabricate efficient, precise, stable, and fast-switching photodetector devices.