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We have studied the utilization of PCDTBT, an alternating poly(2,7-carbazole) derivative, in organic bulk heterojunction solar cells. The effect of polymer molecular weight, PCDTBT:[60]PCBM ratio, and active layer thickness on the device performance is reported. The best performance was obtained when the number-average molecular weights (Mn) are around 20 kDa with a polydispersity index around 2.2. Both PCDTBT:[60]PCBM ratio and active layer thickness affect the light absorption and the charge transport properties. By optimizing these two parameters, power conversion efficiency (PCE) up to 4.35% was reached under calibrated AM1.5G illumination of 100 mW cm−2. When blended with [70]PCBM, PCDTBT exhibited a PCE up to 4.6%. [ABSTRACT FROM AUTHOR]

A fluorescence signal amplification mechanism allowing detection limits for DNA in the zeptomolar range was investigated. Photophysical properties of the molecular system were studied in order to better explain the signal amplification that is observed. We show that the confinement of a fluorescent DNA hybridization transducer in aggregates improves its quantum yield and photostability. Furthermore, we show that the combination of the resonance energy transfer occurring within the aggregates with the use of a conjugated polymer as the hybridization transducer and donor allows ultrafast and efficient energy coupling to the aggregates and can lead to the excitation of a large number of acceptors by only one donor. [ABSTRACT FROM AUTHOR]