Highly foldable transparent conductive films composed of silver nanowire junctions prepared by chemical metal reduction.

A simple method is demonstrated to improve the folding reliability and sheet resistance of silver nanowire (Ag NW)-based transparent conductive films (TCFs) without overcoated layers or complicated processes. As-coated Ag NW film is immersed in a silver-surrounded solution, in which the silver was reduced by Tollen's reagent. Therefore, the reduced silver can be deposited on the surface and crossing of Ag NWs to form a weld-like junction and bind the Ag NWs together, hence decreasing the contact resistance of Ag NW structure at wire-to-wire junctions by increasing the contact surface area. Compared with original Ag NW TCFs, this Ag NW junction structure not only shows compatibility with conventional wet processes, but also demonstrates outstanding flexibility, even when the entire film is folded. This could be attributed to the robustly weld-like wire-to-wire junction of Ag NWs, which enhances its mechanical characteristics. The results demonstrated the feasibility of this alternative approach for the development of an effective low-power-consumption route for fabricating foldable transparent electrodes. Moreover, the results also indicated the practicability of applying this foldable transparent electrode in the fabrication of highly flexible and wearable optoelectronic devices.

Far-field of GaN film-transferred green light-emitting diodes with two-dimensional photonic crystals.

Far-field distributions of GaN-based photonic crystal (PhC) film-transferred light-emitting diodes (FT-LEDs) were investigated. The thickness of the device is about 840 nm. The emission wavelength is around 520 nm. The PhC region is a square lattice with a/lambda around 0.5. Angular-resolved measurements in the Gamma-X and Gamma-M directions were made in the polarized-resolved manner. Guided mode extraction behavior in agreement with the two-dimensional free-photon band calculation was observed. In addition, the pseudo-TM behavior for the non-collinearly coupled modes was observed. The azimuthal-mapping of the angular-resolved spectra revealed the evolution of the collinearly and the non-collinearly coupled modes. Furthermore, the light enhancement of approximately 2.7x and the collimation angle about 102.3 degrees were achieved.

Anisotropy of light extraction from GaN two-dimensional photonic crystals.

Angular distribution of light diffracted out of the plane of two-dimensional photonic crystals (PhC) has been studied in the azimuthal direction with a specially designed waveguide structure. The optical images of the light extraction patterns from the guided photoluminescence light are obtained with laser excitation in the center of the annual structure made on GaN multilayer. For increasing lattice constant, symmetric patterns with varying number of petals according to the symmetry of the PhC are observed. The appearance and disappearance of the petals can be explained using the Ewald construction in the reciprocal space. The dependence of light extraction on the lattice constant and orientation, and incident angle are investigated.