Sulfonic Acid-Doped Polyaniline-<i>co</i>-Polythiophene Showing Enhanced Photocurrent by <i>In Situ</i> Growth of Silver Nanocluster

Recently, a great deal of research has been focused on developing interesting polymeric hybrid materials for different optoelectronic applications. For this purpose, we have synthesized dinonyl disulfonic acid-doped polyaniline-block-polythiophene (PANI-b-PT-DNNDSA, PABT) and dinonyl disulfonic acid-doped polyaniline-ran-polythiophene (PANI-ran-PT-DNNDSA, PART) by emulsion polymerization using an ammonium persulfate (APS) initiator and DNNDSA as the surfactant-cum-dopant. The polymers were characterized by size exclusion chromatography (SEC), 1H NMR, and other spectroscopic techniques. SEC and X-ray photoelectron spectroscopy (XPS) analyses indicate that PABT has the composition PANI34-b-PT16-DNNDSA11. A polymerization mechanism is proposed for both PABT and PART systems. In the PABT-Ag system, the UV–vis, fluorescence, X-ray diffraction (XRD), and microscopic techniques suggest that Ag nanoclusters (AgNCs) are formed and stabilized by sulfur atoms of the PT chain via soft acid–base interactions. XRD data indicate a lamellar structure of PABT/PART systems, and SEM/TEM studies indicate a fibrillar network morphology. However, in PABT-Ag and in PART-Ag systems, sheet morphologies with tiny nanoparticles of raspberry architecture are noticed. Particle size measured from HRTEM images show nanocluster sizes (∼3.5 nm) comprised of about 10 Ag atoms for both PABT-Ag and PART-Ag systems. The absorption peaks of PART showed 5–8 nm blue shifts from PABT attributed to heteroatom nonbonding (pπ–dπ) interactions between closely spaced nitrogen and sulfur atoms of the PART conjugated chain, and fluorescence spectra also supports it. XPS spectra indicate ∼64%/∼61% doping of PANI by DNNDSA in PABT/PART systems. The dc conductivity and current–voltage (I–V) data indicate a semiconducting nature, and AgNCs cause an enhancement of conductivity. PART exhibits ∼3.5 times higher current than a PABT system, and on irradiation with white light, photocurrent increases 2.5–3 times in the AgNC coupled systems, also exhibiting electronic memory. The photocurrent growth in PART is faster than PABT, and in PABT-Ag and PART-Ag systems, growths are faster than those of pure PABT and PART systems, suggesting AgNCs play an important role in the enhanced photocurrent.