High-performance polymer semiconducting heterostructure devices by nitrene-mediated photocrosslinking of alkyl side chains.

Heterostructures are central to the efficient manipulation of charge carriers, excitons and photons for high-performance semiconductor devices. Although these can be formed by stepwise evaporation of molecular semiconductors, they are a considerable challenge for polymers owing to re-dissolution of the underlying layers. Here we demonstrate a simple and versatile photocrosslinking methodology based on sterically hindered bis(fluorophenyl azide)s.

Role of delta-hole-doped interfaces at Ohmic contacts to organic semiconductors.

An electromodulated absorption spectroscopy study of the contact between an organic semiconductor (OSC) poly(2,5-dialkoxy-p-phenylenevinylene) and p-doped poly(3,4-ethylenedioxythiophene) electrodes of different work functions (phivac) reveals direct evidence for the formation of a hole-doped layer at the OSC interface in equilibrium with high-phivac electrodes. When the hole density at this interface exceeds a few 10(11) cm(-2), degenerate "bandlike" polaron states emerge. This appears to be crucial to furnish efficient carrier injection into the bulk of the OSC to achieve Ohmic injection.

Direct evidence for the role of the madelung potential in determining the work function of doped organic semiconductors.

The work function of a model degenerately doped organic semiconductor p-doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) can be systematically tuned over an eV-wide range by exchanging excess matrix protons with spectator cations, without altering the organic semiconductor doping level or polaron density. Ultraviolet photoelectron spectroscopy reveals this to arise not from an interface dipole, but from a bulk effect due to a shift in the Madelung potential set up by the local counter- and spectator-ion structure at the polaron sites. Electrostatic modeling of this potential is in agreement with the observed shift in carrier energetics.

Deoxidation of graphene oxide nanosheets to extended graphenites by "unzipping" elimination.

Low-temperature scanning tunneling microscopy on alkyl-surface-functionalized graphene oxide nanosheets reveals the formation of low-dimensional graphenite nanostructures with extended pi-conjugation at deoxidation temperatures above 150 degrees C. The elimination of these alkyl chains from the surface of the nanosheets does not occur uniformly, but in distinctive patterns that correspond to the formation of an underlying network of graphenite one-dimensional "tracks" and "dots." Atomic-resolution imaging of these graphenite regions reveals a defective honeycomb lattice characteristic of single-layer graphenes.

Direct evidence for delocalization of charge carriers at the Fermi level in a doped conducting polymer.

The infrared absorption spectrum of the polaron charges at the Fermi level EF in a heavily p-doped conducting poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) film has been measured using interferogram-modulated Fourier-transform charge-modulation spectroscopy. The spectrum indicates softer phonons and weaker electron-phonon coupling riding on a strongly redshifted Drude-like electronic transition, different from the population-averaged "bulk" spectrum. This provides direct evidence that the EF holes are sufficiently delocalized even in such disordered materials to reside in an energy continuum (band states) while the rest of the hole population resides in self-localized gap states.

Controlled insulator-to-metal transformation in printable polymer composites with nanometal clusters.

Although organic semiconductors have received the most attention, the development of compatible passive elements, such as interconnects and electrodes, is also central to plastic electronics. For this, ligand-protected metal-cluster films have been shown to anneal at low temperatures below 250 degrees C to highly conductive metal films, but they suffer from cracking and inadequate substrate adhesion. Here, we report printable metal-cluster-polymer nanocomposites that anneal to a controlled-percolation nanostructure without complete sintering of the metal clusters.