Photoelectrochemical and Surface Analysis of CdSe-Poma Composites on Highly Organized Pyrolytic Graphite

Abstract

Over the past decade, semiconductors have been of great interest and currently found applications in computers, cell phones, and medical equipment. Semiconductors provide the basis for the operation of a solar cell in the study of the conversion of solar energy into electricity. This study intended to analyze the stability and efficiency of semiconductor hybrid composites containing cadmium selenide (CdSe) and poly(o-methoxyaniline) (POMA), in the presence of light. The deposition of the CdSe-POMA composites was performed through electrochemical cycling on highly organized pyrolytic graphite (HOPG) surfaces. The composites differed in the order, in which the two components were deposited: (1) CdSe before POMA (CdSe/POMA), (2) POMA before CdSe (POMA/CdSe), and (3) CdSe and POMA simultaneously (CdSe+POMA). The CdSe/POMA and POMA/CdSe composites were deposited in their respective orders, with CdSe layer deposited for 20 cycles via cyclic voltammetry from the solution containing 5 mM CdSO4 and 1 mM SeO2 in 0.1 M HClO4, and POMA film polymerized for 5 cycles from the solution containing 0.06 M o-anisidine in 0.1 M HClO4. The deposition of CdSe+POMA was performed for 20 cycles via electrochemical cycling in the solution of 5 mM CdSO4 + 1 mM SeO2 and 0.06 M o-anisidine in 0.1M HClO4. The photoelectrochemical studies of the created composites consisted of cyclic voltammetry, open circuit potentiometry and chronoamperometry were performed in the 0.1M Na2SO3 solution. The composite of CdSe/POMA presented the greatest photopotential around 220 mV, while POMA/CdSe (30 mV) and CdSe+POMA (14 mV) showed much smaller photopotential values. The chronoamperometric studies found that CdSe/POMA had the greatest photocurrent density of 17 μA/cm2, while POMA/CdSe (0.05 μA/cm2) and CdSe+POMA (0.42 μA/cm2) had substantially smaller photocurrent density. The POMA/CdSe and CdSe+POMA composites proved to be less stable and less photo-active. Following photostudies, the surface morphology and composition of these hybrids were analyzed using X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The surface analysis found a greater degree of degradation of the other two composites (POMA/CdSe, CdSe+POMA), indicating that the polymer deposited above the CdSe layer in the CdSe/POMA composite may be crucial in lessening the degree of degradation resulting from the photo-exposure.