Graphene field effect transistor (G-FET) biosensors exhibit high sensitivity owing to their high electron/hole mobilities and unique 2D nature. However, a baseline drift is observed in their response in aqueous environment, making it difficult to analyze their response against target molecules. Here, we present a computational approach to build state-space models (SSMs) for the time-series data of a G-FET biosensor; the approach helps separate the response against target molecules from the baseline drift. The charge neutral point of the G-FET sensor was continuously measured while sensing target molecules. The obtained time-series data were modeled using the proposed SSMs. The model parameters were estimated through Markov chain Monte Carlo methods. The SSMs were evaluated using the widely-applicable Bayesian information criterion. The SSMs well fitted the time-series data of the G-FET biosensor, and the sensor response to target molecules was extracted from the baseline-drift data.
Active-layer morphology critically affects the performance of organic photovoltaic cells, and thus its optimization is a key toward the achievement of high-efficiency devices. However, the optimization of active-layer morphology is sometimes challenging because of the intrinsic properties of materials such as strong self-aggregating nature or low miscibility. This study postulates that the "photoprecursor approach" can serve as an effective means to prepare well-performing bulk-heterojunction (BHJ) layers containing highly aggregating molecular semiconductors. In the photoprecursor approach, a photoreactive precursor compound is solution-deposited and then converted in situ to a semiconducting material. This study employs 2,6-di(2-thienyl)anthracene (DTA) and [6,6]-phenyl-C71-butyric acid methyl ester as p- and n-type materials, respectively, in which DTA is generated by the photoprecursor approach from the corresponding α-diketone-type derivative DTADK. When only chloroform is used as a cast solvent, the photovoltaic performance of the resulting BHJ films is severely limited because of unfavorable film morphology. The addition of a high-boiling-point cosolvent, o-dichlorobenzene (o-DCB), to the cast solution leads to significant improvement such that the resulting active layers afford up to approximately 5 times higher power conversion efficiencies. The film structure is investigated by two-dimensional grazing-incident wide-angle X-ray diffraction, atomic force microscopy, and fluorescence microspectroscopy to demonstrate that the use of o-DCB leads to improvement in film crystallinity and increase in charge-carrier generation efficiency. The change in film structure is assumed to originate from dynamic molecular motion enabled by the existence of solvent during the in situ photoreaction. The unique features of the photoprecursor approach will be beneficial in extending the material and processing scopes for the development of organic thin-film devices.
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