Exciton

About: Exciton is a research topic. Over the lifetime, 31603 publications have been published within this topic receiving 810642 citations.

Efficiency of exciton and charge carrier photogeneration in a semiconducting polymer.

Abstract: We determine the efficiencies for the formation of excitons and charge carriers following ultrafast photoexcitation of a semiconducting polymer (MEH-PPV). The simultaneous, quantitative determination of exciton and charge photoyields is achieved through subpicosecond studies of both the real and the imaginary components of the complex conductivity over a wide frequency range. Predominantly excitons, with near-unity quantum efficiency, are generated on excitation, while only a very small fraction ($l{10}^{\ensuremath{-}2}$) of free charges are initially excited, consistent with rapid ($\ensuremath{\sim}100\text{ }\text{ }\mathrm{fs}$) hot exciton dissociation. These initial charges are very short lived, decaying on subpicosecond time scales.

Functionalized carbon nanotubes in donor/acceptor-type photovoltaic devices

Abstract: We have introduced functionalized multiwalled carbon nanotubes (CNTs) in donor/acceptor-type photovoltaic devices. We fabricated the devices based on heterostructure between polymer-CNT composite and buckminsterfullerene (C60) layers. Due to the functional groups of the CNTs, a homogeneous blend of CNT-polymer composite could be obtained. In the composite, the nanotubes acted as exciton dissociation sites and also hopping centers for hole transport. The CNTs in the polymer-CNT∕C60 device provided higher exciton dissociation volume and increased mobility for carrier transport. We have observed an increase in open-circuit voltage and short-circuit current in the polymer-CNT∕C60 devices as compared to the polymer∕C60 ones.

What Controls the Rate of Ultrafast Charge Transfer and Charge Separation Efficiency in Organic Photovoltaic Blends

Abstract: In solar energy harvesting devices based on molecular semiconductors, such as organic photovoltaics (OPVs) and artificial photosynthetic systems, Frenkel excitons must be dissociated via charge transfer at heterojunctions to yield free charges. What controls the rate and efficiency of charge transfer and charge separation is an important question, as it determines the overall power conversion efficiency (PCE) of these systems. In bulk heterojunctions between polymer donor and fullerene acceptors, which provide a model system to understand the fundamental dynamics of electron transfer in molecular systems, it has been established that the first step of photoinduced electron transfer can be fast, of order 100 fs. But here we report the first study which correlates differences in the electron transfer rate with electronic structure and morphology, achieved with sub-20 fs time resolution pump–probe spectroscopy. We vary both the fullerene substitution and donor/fullerene ratio which allow us to control both a...

Electroluminescence in organic thin films

Abstract: Mechanism of electroluminescence in organic dye films, mechanisms of carrier injection, carrier transport, carrier recombination, creation of molecular excitons, movement of molecular excitons, and emission from molecular excitons, is described. Using high performance electroluminescent devices, three attempts towards novel fields of photophysics and photochemistry of organic solids were performed. First, confinement of molecular excitons within a molecular-size area was reported. Second, emission from triplet excitons produced by electric excitation was observed. Third, the presence of quantum optical size effect of radiation field in organic thin films was demonstrated.