We realize p- and n-type doping of the organic semiconductor zinc-phthalocyanine using a novel strong organic donor. This allows us to demonstrate the first stable and reproducible organic p-n homojunctions. The diodes show very high built-in potentials, attractive, e.g., for organic solar cells. However, the diode characteristics cannot be described by the standard Shockley theory of the p-n junction since the ideality factor strongly increases with decreasing temperature. We show that this behavior can be explained by deviations from the Einstein relation for disordered materials.
Several electrochemically active polypyridine-metal complexes are isolated in the formally zero-charged state
via reductive electrocrystallization, and are thermally evaporated to form conducting thin films with low
work functions. Solution-phase cyclic voltammetry of the parent complexes is used to predict the work function
of these materials. The reduced films are used as cathode materials in organic light-emitting devices, in place
of the commonly used low work function metals such as calcium and aluminum. These reduced complexes
represent a new class of materials available for use as electron-injecting contacts in organic electroluminescent
devices.
A series of conducting polymers have been prepared through thermal polymerization of transition-metal diimine complexes. The as-polymerized material is electrochemically converted into its formally zerovalent form. Due to the proximity of the half-wave potentials of the formal 1+/0 and 0/1- couples, there is substantial disproportionation of the redox sites at room temperature, resulting in a conductive tervalent mixed-valent material. The redox processes that give rise to this mixed-valent material are predominantly ligand-based, and therefore are highly sensitive to substitution on the ligand periphery. Solution redox chemistry of the monomer can be used to accurately predict the work function of the corresponding zerovalent conducting polymer, which has been verified by ultraviolet photoelectron spectroscopy. Many of these materials have especially low work functions (<3.6 eV) making them appropriate materials to use as cathode materials in organic light-emitting devices (OLEDs). Working examples of tris(8-hydroxyquinoline)aluminum(III)-based OLEDs have been fabricated using one of these polymers as a cathode.
Redox polymers that are both reducible and oxidizable can be
driven to disproportionate when sufficiently
large potential biases are applied across the polymer. Moreover,
if the polymer is ionic in its original form,
this disproportionation can be driven to occur without changes in the
net ionic content of the polymer (the
so-called ion-blocked case). In the first part of this paper we
provide a theoretical description of the steady-state redox gradients that are established in ion-blocked multivalent
redox polymers under voltage bias. In
the second part of the paper a similar treatment is developed for
ion-blocked redox polymer bilayers. The
bilayer systems considered are ones in which the oxidation reaction is
assumed to be sequestered entirely in
one of the polymer layers and the reduction entirely in the other.
The two types of polymer systems are
compared. Also, comparisons are made between the predicted
behavior under ion-blocked and non-ion-blocked conditions. Finally the potential advantages of bilayer
polymers in applications such as solid-state
electrochemically generated luminescence are discussed.
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