A versatile lead iodide particle synthesis and film surface analysis for optoelectronics

Abstract

Lead (II) iodide, PbI2, semiconductor was synthesized using versatile methods such as hydrothermal, refluxing, solid-state reaction, and co-precipitation for optoelectronics. All the PbI2 particles exhibited hexagonal-layered 2H structure in which the average crystallite size and optical bandgap (Eg) were 57 ± 10 nm and 2.31 eV, respectively. Then, PbI2films were prepared using dimethyl sulfoxide (DMSO) or dimethylformamide (DMF) on the top of a mesoporous TiO2 layer, yielding a wider Eg of 2.33–2.36. Finally, through water contact angle measurement, the surface and interfacial properties of the thin film were characterized, exhibiting initial solid-vapor surface tension (γsv) of 6.1–6.4 mJ/m2 and solubility parameter (δ) of 4.51–4.62 (cal/cm3)1/2. However, when these PbI2 films were exposed to H2O molecules in air, δ changes from 4.62 to 7.28 (cal/cm3)1/2 for PbI2 (DMSO) film or 4.51 to 12.98 (cal/cm3)1/2 for the PbI2 (DMF) film, respectively. Finally, by employing the theory of melting point depression combined with the Flory-Huggins lattice theory, the interfacial interactions between PbI2 and regioregular poly (3-hexylthiophene-2,5-diyl) were qualitatively characterized. The smaller the χ interaction parameter, the more depressed the melting point.