DEPOSITION AND INVESTIGATION OF SELENIDES THIN FILMS ON POLYAMIDE FOR OPTOELECTRONIC APPLICATIONS

Ordered nanoscale sized a-Se, CdSe and Ag₂Se films on the polymers are the promising compounds for various applications because of its potential physicochemical and optoelectronic properties such as conductivity, wide energy band gap and high absorbance coefficient [1, 2]. The chemical synthesis methods based on solution-phase procedures provide an excellent route to fabricate nano-selenium and nano-selenides. This work aims to synthesize and characterize a-Se/PA, Cd-Se/PA and Ag-Cd-Se/PA composites. These composites obtained applying different chemical synthesis methods: the a-Se/PA via chemical bath deposition at room temperature, the Cd-Se/PA by successive ionic layer adsorption and reaction at 80 °C, and the Ag-Cd-Se/PA by cation exchange at room temperature, according to the following reactions (Eq. 1-3):

$$Na_2SeO_3(aq) + 2Na_2SO_3(aq) + H_2SO_4(aq) \rightarrow Se(s) + 3Na_2SO_4(aq) + H_2O(l),\tag{1}$$$$3Se(s) + 3Cd^{2+}(aq) + 3H_2O(l) \rightarrow 2CdSe(s) + CdSeO_3(s) + 6H^{+}(aq),\tag{2}$$$$3Se(s) + 6Ag^{+}(aq) + 3H_2O(l) \rightarrow 2Ag_2Se(s) + Ag_2SeO_3(s) + 6H^{+}(aq).\tag{3}$$

In order to have a deep understanding of the relationship between the composition and the end-use properties of obtained composites, we mainly focused on the description of the microstructure, morphology and optical properties. The X-Ray Diffraction (XRD) analysis of the samples were performed on the Bruker Advance D8 diffractometer. Scanning Electron Microscopy/Energy-Dispersive X-Ray Spectroscopy (SEM/EDS) measurements were performed by using a Hitachi S-3400N microscope equipped with the Bruker Quad 5040 EDS system. Atomic force microscopy (AFM) imaging were carried out using a NanoWizard 3 NanoScience microscope. The ultraviolet-visible (UV-Vis) spectrum were recorded using a Spectronic Genesys 8 UV/Visible spectrophotometer.

Investigation of the surface morphology using AFM (Fig. 1) and SEM corroborates the change in morphology depending on chemical composition deposited films. In a-Se/PA composite selenium was amorphous (a-Se). In Cd-Se/PA composite the diffraction peaks indexed as hexagonal CdSe and monoclinic Se₈ which occur after a-Se crystallization at higher temperature. Ag-Cd-Se/PA composite XRD patterns showed crystalline composition with hexagonal CdSe, orthorhombic Ag₂Se, metallic Ag and monoclinic Se₈.

Relatively high Urbach energy values indicate the formation of disordered structures, which correlates with heterogeneous surface morphology and composition. The optical properties of the obtained composites indicate a shift in the energy band gap from 2.23 eV to 1.64 eV with a stepwise incorporation of Cd²⁺ and Ag⁺ (Table 1). The energy band gap is suitably located in the visible solar energy region, which make these composites ideal for solar energy harvesting.