Although small-molecule organic solar cells (SMOSCs) have shown increasingly promising prospects as a source of solar power, there have been few studies concerning the photophysics of these systems. Here, we report the time scale and efficiency of charge separation and recombination in a vapor-deposited SMOSC material that produces 5.81% power conversion efficiency. Transient absorption and time-resolved photoluminescence (trPL) studies of thin film blends comprising DTDCTB, a narrow-band gap electron donor, and either C60 or C70 as an electron acceptor show that charge separation occurs in ~100 fs, while charge recombination takes place over sub-ns and ns time scales. trPL indicates a donor electron-hole pair lifetime of ~33 ps in the neat film and reveals that ~20% of donors fail to charge separate in donor-acceptor mixed films, likely owing to some spatially extended donor-rich regions that interact poorly with acceptors. Our results suggest that morphological manipulations of this material could further improve device efficiency.

The "all carbon" organic solar cells (OSCs) based on the homocyclic molecule tetraphenyldibenzoperiflanthene (DBP) as a donor and C60 as an acceptor were comprehensively characterized. The optimized planar-mixed heterojunction device with a DBP:C60 mixture ratio of DBP : C60 (1 : 2) exhibited a power conversion efficiency of 4.47%. To understand why DBP possesses such advantageous characteristics, the correlations of the morphology, molecular stacking, carrier dynamics and performance of DBP:fullerene-based devices have been systematically studied. First, the face-on stacked DBP molecules could enhance both the absorption of light and the charge carrier mobility. Second, DBP : C60 (1 : 2) thin films with optimized domain sizes and partially interconnected acceptor grains led to the most balanced carrier mobility and the lowest bimolecular recombination in devices. Finally, the DBP molecules were found to stack closely using grazing incidence wide-angle X-ray scattering measurements, with a π-π stacking spacing of 4.58 Å, indicating an effective molecular orbital overlap in DBP. The study not only reveals the promising characteristics of DBP as a donor in OSCs but the clear correlations of the thin-film nano-morphology, molecular stacking, carrier mobility and charge recombination found here could also provide insights into the characterization methodology and optimization of the small molecule OSCs.

In this research, we have designed, fabricated and characterized an electrical double layer (EDL)-gated AlGaN/GaN high electron mobility transistor (HEMT) biosensor array to study the transmembrane potential changes of cells. The sensor array platform is designed to detect and count circulating tumor cells (CTCs) of colorectal cancer (CRC) and investigate cellular bioelectric signals. Using the EDL FET biosensor platform, cellular responses can be studied in physiological salt concentrations, thereby eliminating complex automation. Upon investigation, we discovered that our sensor response follows the transmembrane potential changes of captured cells. Our whole cell sensor platform can be used to monitor the dynamic changes in the membrane potential of cells. The effects of continuously changing electrolyte ion concentrations and ion channel blocking using cadmium are investigated. This methodology has the potential to be used as an electrophysiological probe for studying ion channel gating and the interaction of biomolecules in cells. The sensor can also be a point-of-care diagnostic tool for rapid screening of diseases.

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