A Multifunctional Interlayer for Solution Processed High Performance Indium Oxide Transistors.

Multiple functionality of tungsten polyoxometalate (POM) has been achieved applying it as interfacial layer for solution processed high performance In2O3 thin film transistors, which results in overall improvement of device performance. This approach not only reduces off-current of the device by more than two orders of magnitude, but also leads to a threshold voltage reduction, as well as significantly enhances the mobility through facilitated charge injection from the electrode to the active layer. Such a mechanism has been elucidated through morphological and spectroscopic studies.

Multilayer Langmuir-Blodgett films as diffractive external 3D photonic crystal in blue OLEDs.

Three-dimensional Langmuir-Blodgett films made of silica beads are theoretically and experimentally investigated in order to improve the relatively small efficiency of blue OLEDs. Using films made of 5 layers of beads, we fabricated OLEDs emitting at 476 nm, and measured a gain of around 40% on their external quantum efficiency. An optical model has been developed to accurately handle the fact that the organic emitting layer and the photonic extraction layer are separated by a distance greater than 1000 wavelength. The latter also permits to describe rapidly this three-dimensional optical OLED cavity, without redoing all the numerical simulations when the optical properties of the organic layers are changed (material index, thicknesses).

Light trapping efficiency of organic solar cells with large period photonic crystals.

We study the optical properties of a 2D Photonic Crystal (PC) inserted in the upper ITO electrode of a classical P3HT:PCBM solar architecture with an ultra-thin active layer. First, we analyze the optical response of the system when only the active layer is supposed to absorb light. This allows us to observe clear photonic crystal resonances in the absorption spectrum, which increase the cell efficiency even if the period of the PC is higher than the wavelength. This is in apparent contradiction with the common belief that PC should work in subwavelength regime. Then, by turning to a real system (with optical losses in all the layers), an optimized PC design is proposed, where the maximum of efficiency is obtained for a PC period of 1200 nm, much larger than visible wavelength.