Preparation and characterization of CdSe/POMA photoactive composites electrochemically grown on HOPG surfaces

Visible light driven photoactive inorganic-organic hybrid composites were prepared containing cadmium selenide CdSe) and poly(o-methoxyaniline) nanofilms. The films were fabricated in three different configurations: i. Composite of CdSe deposited onto HOPG with o-methoxyaniline (POMA) deposited on top (HOPG/CdSe/POMA), ii. Composite of POMA deposited onto the HOPG substrate with CdSe deposited on top (HOPG/POMA/CdSe), iii. Composite made through the simultaneous deposition of CdSe and POMA (HOPG/(CdSe/POMA)) on HOPG substrate. The hotoactivity and physico-chemical properties of the fabricated composites were examined through electrochemical, XPS, Raman, in situ AFM and STS techniques. The changes in morphology, optical, spectroscopic, photoactive properties and elemental composition of the hybrids were monitored depending on the composite design, namely: number of the deposition cycles or order of component deposition. The HOPG/CdSe/POMA was identified as the most photoactive and stable composite and hence this material was further examined for its properties. In all cases of the fabricated hybrids, n-type and p-type photocurrents were observed. As the thickness of POMA increases, the p-type photocurrent decreases, while the n-type photocurrent increases. It is proposed that the p-type photocurrent observed is due to the presence of elemental selenium. The n-type photocurrent is attributed to CdSe layer. The amount of the polymer was optimized in order to maximize the photoactivity of the fabricated composite. The ptimal POMA thickness, prepared in 5 deposition cycles, was determined by the AFM scratching technique to be 150 nm prepared. The highest photocurrent (224 μAcm−2) and highest photopotential (230 mV) were observed for the omposite deposited on HOPG substrate with 20 deposition cycles of CdSe and 5 deposition cycles of POMA. The bandgap of the HOPG/ CdSe/POMA composite was determined by the STS technique to be 2.2 eV.