Volume 12 Issue 7, July 2013

In all likelihood, cheap and bright white organic light-emitting diodes will someday light up our homes. Three-dimensional models can now simulate the dynamics of charges and excitons governing the operation of these light sources and predict their performance with molecular precision.

Fabricating thin films of organic semiconductors that have molecular order across large areas has proved challenging. Now, three complementary approaches — molecular design, fluid-flow control and the use of nucleating agents — offer unprecedented opportunities for next-generation optoelectronic applications.

A complete understanding of the mechanism underpinning high-temperature superconductivity is notoriously elusive. The growing body of evidence suggesting that monolayer iron selenide superconducts up to 65 K indicates it may become an ideal model system for testing theoretical ideas.

Employing a semiconducting electrode in a ferroelectric tunnel junction boosts the resistance switching effect.

The unconventional superconductivity associated with iron pnictide materials has been the subject of intense interest. Using an annealing procedure to control the charge-carrier concentration, the behaviour of an FeSe monolayer deposited on SrTiO₃ is now investigated, and indications of superconductivity at temperatures up to 65 K observed.

Controlling the direction of propagation of domain walls in magnetic nanowires is essential for their use in proposed device applications. It is now shown that Dzyaloshinskii–Moriya interactions determine the chirality of domain walls in metallic ferromagnets placed between a heavy metal and an oxide, which in turn means the direction of propagation can be determined by choosing suitable material properties.

A ferroelectric tunnelling heterostructure is presented in which both the height and the width of the tunnelling barrier can be electrically modulated, leading to a greatly enhanced tunnelling electroresistance. In Pt/BaTiO₃/Nb:SrTiO₃ heterostructures, an ON/OFF conductance ratio that is about an order of magnitude greater than those reported in normal ferroelectric tunnelling junctions, is demonstrated at room temperature.

The conversion of a spin current into an electric signal is known as the inverse spin Hall effect, and is expected to enable the full potential of spintronic devices to be realized. Although the effect has been extensively studied in inorganic metals and semiconductors, it is now shown also to occur in a solution-processed organic polymer placed in proximity to a magnetic insulator.

Difficulties in controlling the nucleation and growth of thin films of organic semiconductors have impaired progress in organic electronics. Now, efficient control of the crystallite nucleation and microstructure of a broad range of organic semiconductors without detriment to their electronic properties has been achieved through the addition of small quantities of additives—a widely used strategy in bulk polymer crystallization.

Iron pnictide superconductors represent a suggestive alternative to cuprate superconductors for achieving high transition temperatures. Using in situ angle-resolved photoemission spectroscopy, the electronic properties of FeSe are examined as a function of film thickness, providing valuable insights into the mechanism driving the superconductivity in this material.

The ferroelectric properties of BiFeO₃ have been the subject of extensive study. Using a range of experimental tools and numerical modelling, it is now shown that its ferroic properties can also be manipulated by strain effects, giving rise to a variety of magnonic phenomena.

Although high proton conductivity and chemical stability in yttrium-doped barium zirconate are of interest for intermediate-temperature solid-oxide fuel cells, there are remaining issues regarding its defect chemistry and macroscopic proton-transport mechanism. Proton transport in this compound is shown to be limited by proton–dopant association, and the presence of two types of proton environment above room temperature are observed, reflecting differences in proton–dopant configurations.

The variety of electronic processes occurring within an organic light-emitting diode (OLED) make the prediction of their emission characteristics problematic. It is now shown that all the relevant processes occurring in a stacked OLED can be modelled down to the molecular scale, in turn leading to accurate emission profiles.

The molecular alignment and order of conjugated polymers within organic electronic devices is an important consideration for the enhancement of device performance. Now, some design rules are revealed that promote the directed alignment of the polymers and result in the fabrication of well-aligned films with highly anisotropic carrier mobilities.

Solution printing of organic semiconductors could in principle be scaled to industrial needs, yet attaining aligned single-crystals directly with this method has been challenging. By using a micropillar-patterned printing blade designed to enhance the control of crystal nucleation and growth, thin films of macroscopic, highly aligned single crystals of organic semiconductors can now be fabricated.

A transparent organic field-effect transistor allows the stimulation and recording of the bioelectrical activity of primary neural cells. The cells grow, differentiate and function on the device, which then provides the electrical stimulation, and enables the recording of extracellular current and optical imaging of the modulation of neuronal membrane potential.

The establishment of high-tech products relying on organic semiconductors demonstrates the remarkable technological maturity and competitiveness of these materials. This focus issue explores the latest strategies for improving the processability and performance of conducting molecular systems and polymers that make them attractive for an ever-growing range of technological applications.