Silver Nanoparticles in Ammonia Sensing and Photovoltaics

Nanocomposite films (NCF) containing silver nanoparticles (AgNPs), separated by thin layers of silica/poly-4-vinylpyridine/polyvinylpyrrolidone, were fabricated via drop casting, spin coating, dip coating on glass substrate and drop casting on nylon filter membranes. The more uniform films were produced by drop casting on nylon filter membranes due to their solvent wicking properties. The films demonstrate electrical conductivity that varies in response to moist ammonia and water vapors. The changes in conductivity are attributed to hydrogen bonding between ammonia and water molecules with the silica/polymer layers, as well as the direct adsorption of ammonia onto the silver surface. Notably, NCFs with polyvinylpyrrolidone layers exhibited a limit of detection of 0.4 ppm for ammonia, even in the presence of interfering water vapor. It is proposed that the films could be further developed as ammonia sensors for environmental and biomedical applications. The novelty of this work relates to achieving low detection limit in the presence of saturated water vapor as well as a development of new simple and reproducible fabrication technique. This work is published in Sensors and Actuators B: Chemical journal. Silver nanoparticles (AgNPs) exhibit highly efficient interaction with light across visible and near IR spectral ranges due to the excitation of plasmon resonances and can potentially function as an effective light capturing antenna. Hybrid nanostructure containing Ag plasmonic core and photosensitive Ag2S semiconductor layer were fabricated and incorporated into photovoltaic (PV) devices that were expected to exhibit enhanced performance. Contrary to the initial expectations, it was established that the direct contact between Ag2S photosensitive semiconductor layer with the metallic silver core provided an additional mechanism for the recombination of photogenerated electron hole pairs thus reducing the performance of the devises. Plasmonic AgNPs were synthesized with a thin electrically insulated shell to alleviate this recombination mechanism and integrated into the PV devices containing Ag2S photosensitive semiconductor. Embedding the insulated plasmonic AgNPs into the semiconductor resulted in a 20.4% enhancement of the photo conversion efficiency (PCE) as compared to the same PV devices without plasmonic particles. The novelty of this work relates to the identification of electron hole recombination mechanism within plasmonic metal nanostructures that leads to the reduced performance of PVs. This has broad applicability to all PV devices that utilize plasmon resonances to enhance their performance. A general solution was developed based on electrically insulating plasmonic nanoparticles with a thin dielectric shell. The significant improvement of the PCE was achieved because of the locally enhanced electromagnetic field associated with plasmon oscillations. All structures were characterized using optical microscopy, atomic force microscopy, UV-Vis spectroscopy, SEM, Raman, and XRD.