Experimental design for the determination of the injection barrier height at metal/organic interfaces using temperature dependent current-voltage measurements

Facile synthesis of a semiconducting bithiophene-azine polymer and its application for organic thin film transistors and organic photovoltaics

A new azine polymer poly(4,4'-didodecyl-2,2'-bithiophene-azine) (PDDBTA) was synthesized in only three steps. PDDBTA showed hole mobilities of up to 4.1 × 10-2 cm2 V-1 s-1 in organic thin film transistors (OTFTs) as a p-channel material. As a donor in organic photovoltaics (OPVs), power conversion efficiencies (PCEs) of up to 2.18% were achieved, which is the first example of using an azine-based polymer for OPVs. These preliminary results demonstrate the potential of bithiophene-azine polymers as a new type of low-cost semiconductor material for OPVs and other organic electronics.

Blue phosphorescent N-heterocyclic carbene chelated Pt(ii) complexes with an α-duryl-β-diketonato ancillary ligand

Blue phosphorescent Pt(ii) complexes that display bright blue emission in the solid state have been obtained employing NHC-based C^∧C*-chelate ligands and an α-duryl-β-diketonato ancillary ligand that provides steric blocking to minimize intermolecular interactions.

Nanoscale geometric electric field enhancement in organic photovoltaics

Generic design rules for electrode-organic semiconductor contacts that transcend specific materials are urgently required to guide the development of new electrodes and provide a framework for engineering this important class of interface. Herein a novel nanostructured window electrode is utilized in conjunction with three-dimensional electrostatic modeling to elucidate the importance of geometric electric field enhancement effects at the electrode interfaces in organic photovoltaics. The results of this study show that nanoscale protrusions at the electrode surfaces in organic photovoltaics dramatically improve the efficiency of photogenerated charge carrier extraction to the external circuit and that the origin of this improvement is the local amplification of the electrostatic field in the vicinity of said protrusions. This wholly geometric approach to engineering electrodes at the nanoscale is materials generic and can be employed to enhance the efficiency of charge carrier injection or extraction in a wide range of organic electronic devices.

N-heterocyclic carbazole-based hosts for simplified single-layer phosphorescent OLEDs with high efficiencies

Highly efficient single-layer organic light-emitting diodes (OLEDs) are demonstrated using new N-heterocyclic carbazole-based host materials. Phosphorescent OLEDs with a structure of ITO/MoO(3) /host/host:dopant/host/Cs(2) CO(3) /Al are fabricated in which the new materials act simultaneously as electron-transport, hole-transport, and host layer. Devices with maximum current and external quantum efficiencies of 92.2 cd A(-1) and 26.8% are achieved, the highest reported to date for a single-layer OLED.

The impact of the Fermi-Dirac distribution on charge injection at metal/organic interfaces

The Fermi level has historically been assumed to be the only energy-level from which carriers are injected at metal/semiconductor interfaces. In traditional semiconductor device physics, this approximation is reasonable as the thermal distribution of delocalized states in the semiconductor tends to dominate device characteristics. However, in the case of organic semiconductors the weak intermolecular interactions results in highly localized electronic states, such that the thermal distribution of carriers in the metal may also influence device characteristics. In this work we demonstrate that the Fermi-Dirac distribution of carriers in the metal has a much more significant impact on charge injection at metal/organic interfaces than has previously been assumed. An injection model which includes the effect of the Fermi-Dirac electron distribution was proposed. This model has been tested against experimental data and was found to provide a better physical description of charge injection. This finding indicates that the thermal distribution of electronic states in the metal should, in general, be considered in the study of metal/organic interfaces.