Photoinduced charge transfer is a key step in the mechanism of charge generation in organic solar cells. Charge transfer typically occurs from a photoexcited conjugated polymer donor to an electron acceptor. In an effort to better understand the primary events in solar cells, we have investigated photoinduced charge transfer in model donor-acceptor systems consisting of pi-conjugated oligomer donors that are covalently linked to diimide electron acceptors. These studies utilized oligo(thiophene), oligo(phenylene ethynylene) and oligo(fluorene) pi-conjugated systems with lengths varying from 4 to 12 repeat units linked to naphthalene diimide electron acceptors. Excitation with 100 femtosecond pulses at wavelengths correspoinding to the conjugated oligomer absorption band(s) leads to rapid photoinduced charge transfer to produce a charge separated state, (oligomer+)-(NDI-), which subsequently decays on timescales ranging from 100 ps to 5 ns. The dynamics of the forward and reverse electron transfer reactions depend strongly on the structure and length of the pi-conjugated oligomers, with the fastest rates occurring for oligo(thiophene)s, and considerably slower rates for oligo(phenylene ethynylene)s. The talk will discuss the structure-property relationships and energetic correlations that control the dynamics of charge separation and recombination.
The demand for novel optoelectronic and photonic technologies has fueled an intense research effort to synthesize and
characterize nanostructured semiconductor materials with unique properties that lend themselves to technological
innovation. Zinc Oxide has emerged as an attractive candidate for a variety of applications, due in part to a large second
order nonlinear susceptibility, its wide band-gap and large exciton binding energy. We have used time-resolved
nonlinear two-photon emission and second harmonic generation microscopy to characterize the optical properties and
excited state dynamics of individual rods. Ultrafast emission microscopy is used to follow the trapping dynamics of
photoexcited charge carriers. Our results show a time-dependent red-shift in the trap emission band that is interpreted as
arising from carrier percolation through trap states. In a second series of experiments, second harmonic generation
(SHG) microscopy illustrates the connection between the optical mode structure of the object and its nonlinear mixing
efficiency. Images show a periodic modulation in the SHG efficiency that is symmetrically situated relative to the rod
midpoint. This phenomenon arises when the fundamental optical field couples into standing wave resonator modes of the
structure and is a direct manifestation of the tapered shape of the rod.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.