2 research outputs found
Balanced Ambipolar Organic Field-Effect Transistors by Polymer Preaggregation
Ambipolar
organic field-effect transistors (OFETs) based on heterojunction
active films still suffer from an imbalance in the transport of electrons
and holes. This problem is related to an uncontrolled phase separation
between the donor and acceptor organic semiconductors in the thin
films. In this work, we have developed a concept to improve the phase
separation in heterojunction transistors to enhance their ambipolar
performance. This concept is based on preaggregation of the donor
polymer, in this case poly(3-hexylthiophene) (P3HT), before solution
mixing with the small-molecular-weight acceptor, phenyl-C61-butyric
acid methyl ester (PCBM). The resulting heterojunction transistor
morphology consists of self-assembled P3HT fibers embedded in a PCBM
matrix, ensuring balanced mobilities reaching 0.01 cm<sup>2</sup>/V
s for both holes and electrons. These are the highest mobility values
reported so far for ambipolar OFETs based on P3HT/PCBM blends. Preaggregation
of the conjugated polymer before fabricating binary blends can be
regarded as a general concept for a wider range of semiconducting
systems applicable in organic electronic devices
Structural, Spectroscopic, Electrochemical, and Electroluminescent Properties of Tetraalkoxydinaphthophenazines: New Solution-Processable Nonlinear Azaacenes
A series
of solution-processable tetraalkoxy-substituted dinaphtho[2,3-<i>a</i>:2′,3′-<i>h</i>]phenazines were
synthesized by reductive functionalization of indanthrone (6,15-dihydrodinaphtho[2,3-<i>a</i>:2′,3′-<i>h</i>]phenazine-5,9,14,18-tetraone),
an old intractable dye. The melting point of these new compounds was
found to decrease from 204 °C to 98 °C upon extension of
the number of carbons from 4 to 12 in the alkoxy substituent. All
derivatives show a strong tendency to self-organize in 2D as evidenced
by STM investigations of monolayers deposited on HOPG. The 2D structure
is less dense and shows different alkoxy group interdigitation pattern
as compared to the 3D structure determined from the X-ray diffraction
data obtained for the corresponding single crystals. Electrochemical,
absorption, and emission properties of tetraalkoxy-substituted dinaphtho[2,3-<i>a</i>:2′,3′-<i>h</i>]phenazines, studied
in solution, are essentially independent of the length of the alkoxy
substituents. All derivatives exhibit high photoluminescence quantum
yield, approaching 60%. When molecularly dispersed in a solid matrix
consisting of poly(9-vinylcarbazole) (PVK) (60 wt %) and (2-<i>tert</i>-butylphenyl-5-biphenyl-1,3,4-oxadiazole) (PBD) (40
wt %) (so-called “guest/host configuration”), they show
green electroluminescence due to an effective energy transfer from
the matrix to the luminophore. The best light-emitting diodes were
obtained for the butoxy derivative showing a luminance approaching
1500 cd/m<sup>2</sup> and a luminous efficiency over 0.8 cd/A