Efficient and bright organic light-emitting diodes on single-layer graphene electrodes.

Organic light-emitting diodes are emerging as leading technologies for both high quality display and lighting. However, the transparent conductive electrode used in the current organic light-emitting diode technologies increases the overall cost and has limited bendability for future flexible applications. Here we use single-layer graphene as an alternative flexible transparent conductor, yielding white organic light-emitting diodes with brightness and efficiency sufficient for general lighting. The performance improvement is attributed to the device structure, which allows direct hole injection from the single-layer graphene anode into the light-emitting layers, reducing carrier trapping induced efficiency roll-off. By employing a light out-coupling structure, phosphorescent green organic light-emitting diodes exhibit external quantum efficiency >60%, while phosphorescent white organic light-emitting diodes exhibit external quantum efficiency >45% at 10,000 cd m(-2) with colour rendering index of 85. The power efficiency of white organic light-emitting diodes reaches 80 lm W(-1) at 3,000 cd m(-2), comparable to the most efficient lighting technologies.

Nanoscale chemical templating of Si nanowires seeded with Al.

We describe a new approach for achieving controlled spatial placement of VLS-grown nanowires that uses an oxygen-reactive seed material and an oxygen-containing mask. Oxygen-reactive seed materials are of great interest for electronic applications, yet they cannot be patterned using the approaches developed for noble metal seed materials such as Au. This new process, nanoscale chemical templating, takes advantage of the reactivity of the blanket seed layer by depositing it over a patterned oxide that reacts with the seed material to prevent nanowire growth in undesired locations. Here we demonstrate this technique using Al as the seed material and SiO2 as the mask, and we propose that this methodology will be applicable to other reactive metals that are of interest for nanowire growth. The method has other advantages over conventional patterning approaches for certain applications including reducing patterning steps, flexibility in lithographic techniques, and high growth yields. We demonstrate its application with standard and microsphere lithography. We show a high growth yield and fidelity, with no NWs between openings and a majority of openings occupied by a single vertical nanowire, and discuss the dependence of yield on parameters.