Effect of Gd3+ doping on structural, morphological, optical, dielectric, and nonlinear optical properties of high-quality PbI2 thin films for optoelectronic applications

Herein, we present the fabrication and characterization of Gd:PbI2 thin films from low-cost material using a cost-effective spin-coating technique by taking the Gd content as 1.0, 2.0, and 3.0 wt% in PbI2. Single-phase and good crystallinity films oriented along the c-axis were confirmed by X-ray diffraction and FT-Raman spectroscopy. Size of crystallites increased with Gd concentration and was estimated to be in the range of 16-32 nm. Determination of morphology and size of grains (50-103 nm), and elemental confirmation were carried out by SEM/EDX analysis. Optical transparency of fabricated films was found to be in the range of 72-92%. The energy gap is reduced from 2.31 to 2.05 eV; this makes Gd:PbI2 films highly applicable in solar cells. The stable value of refractive index is estimated to be in the range of 1.85-2.3. Dielectric constant was observed to be reduced with doping and in the range of 2.5-35, and ac conductivity was also reduced by doping; however, both were enhanced with frequency. The values of chi((1)), chi((3)), and n((2)) are found to be in the range of 0.15 to 2.5, 8 x 10(-14) to 6.5 x 10(-9), and 5 x 10(-12) to 4 x 10(-8), respectively.