Gas Sensor Based on Highly Effective Slot-Die Printed PEDOT:PSS@ZnO Hybrid Nanocomposite for Methanol Detection.

This study presents the development of gas sensors based on the PEDOT:PSS@ZnO hybrid active layer slot-die printing aqueous ink. Two different zinc oxide (ZnO) nanoparticles were studied to form the nanocomposites, as well as the use of glass and PET substrates to manufacture the devices. Despite the influence of the morphology of the active layer, all device variations studied here exhibited high response values for methanol gas at room temperature, in addition to presenting good repeatability, reversibility, and the possibility of technology transfer to flexible substrates. Furthermore, PEDOT:PSS@ZnO showed good selectivity to methanol compared to ethanol, ammonia, and CO2. The best devices showed responses greater than 700% in detecting methanol.

Optical Biosensor for the Detection of Infectious Diseases Using the Copolymer F8T2 with Application to COVID-19.

The coronavirus pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has accelerated the development of biosensors based on new materials and techniques. Here, we present our effort to develop a fast and affordable optical biosensor using photoluminescence spectroscopy for anti-SARS-CoV-2 antibody detection. The biosensor was fabricated with a thin layer of the semiconductor polymer Poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-2,2'-bithiophene-5,5'-diyl)] (F8T2) as a signal transducer material. We mounted the biosensors by depositing a layer of F8T2 and an engineered version of RBD from the SARS-CoV-2 spike protein with a tag to promote hydrophobic interaction between the protein and the polymeric surface. We validated the biosensor sensitivity with decreasing anti-RBD polyclonal IgG concentrations and challenged the biosensor specificity with human serum samples from both COVID-19 negative and positive individuals. The antibody binding to the immobilized antigen shifted the F8T2 photoluminescence spectrum even at the low concentration of 0.0125 µg/mL. A volume as small as one drop of serum (100 µL) was sufficient to distinguish a positive from a negative sample without requiring multiple washing steps and secondary antibody reactions.

Morphology and energy transfer study between conjugated polymers thin films: experimental and theoretical approaches.

In this paper, the effect of a silafluorene derivative copolymer, the poly[2,7-(9,9-dioctyl-dibenzosilole)-alt-4,7-bis(thiophene-2-yl)benzo-2,1,3-thiadiazole] (PSiF-DBT) sensitized by a simpler homopolymer, the poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) were investigated in a bilayer and ternary blend configuration. The energy transfer between the polymers prior to electron transfer to the acceptors can be an efficient alternative to photocurrent improvement in photovoltaic devices. The interactions between the two donor polymer films were evaluated optically and morphologically with several experimental techniques and correlated to the photovoltaic performance. Improved photon to charge conversion was observed in the blend films at different device geometries-considering bilayer devices with fullerene and inverted flexible devices blade coated in air conditions with a non-fullerene small molecule acceptor. Resonant Auger spectroscopy using the core-hole clock method was employed to evaluate the ultrafast charge delocalization times of conjugated polymers in the low-femtosecond regime. Density functional theory and time-dependent DFT methods were used to help understand some experimental observations. The results show that the homopolymer can improve the absorption spectra and the nonradiative-energy transfer from MDMO-PPV to PSiF-DBT and act as a photosensitizer in the copolymer units. In addition, the PSiF-DBT blended with MDMO-PPV exhibits a more organized structure than the neat material resulting in better absorption stability of films kept under continuous illumination.

Correlation between structural and optical characteristics of conjugated copolymers differing by a Si bridge atom.

In this study, we investigate two copolymers as electron donors in photovoltaic devices, PFO-DBT (poly[2,7-(9,9-dioctylfluorene)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole]) and its analogue with Si, PSiF-DBT (poly[2,7-(9,9-dioctyl-dibenzosilole)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole]). The results discussed here are related to the influence of heavy atoms on the electrical and morphological properties of the devices. Charge transfer dynamics in the polymeric films were evaluated using the core-hole clock method. Besides that, using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, we investigate the electronic structure and charge transfer properties of the two systems. The charge transfer rates were estimated in the framework of the semiclassical Marcus/Hush theory. We found that the better stacking between the polymer chains for PSiF-DBT provides higher solar absorption capacity in regions of higher wavelengths and faster hole transfer rates. We also obtain a faster electron transfer rate at the PSiF-DBT/C60 interface compared to the PFO-DBT/C60 interface that is mainly related to the difference in the driving force between the two systems. These features help to explain why the organic photovoltaic devices using PSiF-DBT as the active layer exhibited a higher performance compared to devices using PFO-DBT. Here, we show that our results are able to provide important insights about the parameters that can influence the photovoltaic performance of the devices.

Effects of non-halogenated solvent on the main properties of a solution-processed polymeric thin film for photovoltaic applications: a computational study.

Organic photovoltaic (OPV) devices have reached high power conversion efficiencies, but they are usually processed using halogenated toxic solvents. Hence, before OPV devices can be mass-produced by industrial processing, it would be desirable to replace those solvents with eco-friendly ones. Theoretical tools may be then a powerful ally in the search for those new solvents. In order to better understand the mechanisms behind the interaction between solvent and polymer, classical molecular dynamics (MD) calculations were used to produce a thin film of poly(4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl) (PTB7-Th), processed using two different solvents. PTB7-Th is widely applied as a donor material in OPVs. The first solvent is ortho-dichlorobenzene (o-DCB), which is a highly toxic solvent widely used in lab-scale studies. The second solvent is ortho-methylanisole (o-MA), which is an eco-friendly solvent for organic photovoltaic (OPV) manufacturing. Here we use a solvent evaporation protocol to simulate the formation of the PTB7-Th film. We demonstrate that our theoretical MD calculations were able to capture some differences in the macroscopic properties of thin films formed by o-DCB or o-MA evaporation. We found that the interaction of the halogenated solvent with the polymer tends to break the bonds between the lateral thiophenediyl groups and the main chain. We show that those defects may create traps that can affect the charge transport and also can be responsible for a blue shift in the absorption spectrum. Using the Monte Carlo method, we also verified the influence of the resulting MD morphology on the mobility of holes. Our theoretical results showed good agreement with the experimental measurements and both demonstrate that o-MA can be used to make polymer thin films without any loss of key properties for the device performance. The findings here highlight the importance of theoretical results as a guide to the morphological optimization of green processed polymeric films.