Influence of L-Tryptophan on Growth and Optical Properties of PbS Nanocrystalline Thin Films

Abstract

The growth through the green chemical bath of PbS doped systematically with the biomolecule L-tryptophan led to growth of hybrid, inorganic-organic, nanocrystalline thin films onto glass slides at T~80°C. The thickness was found in the range of 230-140 nm. Morphological changes were analyzed using atomic force microscopy (AFM). FTIR (Fourier-transform infrared spectroscopy) spectra showed broad absorption bands located at~3450 cm −1 attributed to stretching of the H 2 O molecules and two small absorption bands located at~2285 cm −1 and~2918 cm −1 along with a strong band at~1385 cm −1 assigned to vibration modes corresponding to CO 2− 3 ions. In the patterns of X-ray diffraction (XRD), the cubic phase was identified in all the samples according to the angular positions 2θ~26 08°, 30.13°, 43.08°, 51.91°, 53.60°, 6251°, 68.98°, and 71.15°. Using the Scherrer formula on the XRD patterns, the grain size (GS) was determined; for the undoped sample,~42 nm was found, whereas for the doped samples,~42-22 nm was found. The electronic charge distribution of L-tryptophan was determined using the molecular electrostatic potential (MEP) to understand the decrease on the GS associated with the interaction of π electrons from conjugated rings and amino-acid functional groups. The absorbance spectra in doped films showed excitonic peaks at~1.8-2.1 eV associated to a higher energy of the 1 S h → 1 S h and 1 P h → 1 P e electronic transitions. Through optical absorption, a shift for the band gap energy was observed from~1.4 eV for the undoped sample and~2.1-2.3 eV for the doped films, respectively. Such behaviour is generally associated with the GS decrease and the effect of quantum confinement; a simple model by calculating changes in Gibbs free energy (ΔG°) for growth of nanocrystals is presented.

Electrochemistry of Inorganic OCT-PbS/HDA and OCT-PbS Photosensitizers Thermalized from Bis(N-diisopropyl-N-octyldithiocarbamato) Pb(II) Molecular Precursors

“…This enables QDSCs to trap the photon energy in the entire UV-Vis spectral region. Wavelengths similar to those obtained in this study for OCT-PbS/HDA have been reported as produced by the recombination of excitons shallowly trapped in electron-hole pairs by [32,43]. Table 1 and Figure 9 illustrate the current-voltage (J−V) characteristics of the QDSSCs of OCT-PbS/HDA and OCT-PbS photosensitizers under illumination.…”

“…The height clusters of both samples depicted an insignificant change around 0.328 and 1.35 µm, which connotes smaller nanocrystals [35]. The images displayed small spherical nanocrystals with uniform distribution and size in the crystalline phase in both samples, indicating compact nanoparticles [32] and in further agreement with the XRD results. In order to evaluate electrocatalytic abilities and the reaction kinetics of PbS/HDA and PbS 120 photosensitizers, the cyclic voltammetry (CV) measurements were adopted with three-electrode 121 systems [36].…”

“…The structural disorder emanating from the lattice strain is due to shifts in the diffraction lines. These shifts are typical reflections associated with incorporation into the crystal lattice [28][29][30][31][32]. 96 and 3.623 nm, respectively.…”