We investigate the effect of the incorporation of CdSe quantum dots (QD) in the standard ITO/TPD/Alq3/Al organic light emitting diodes (OLED's). The OLED's structures have been prepared in a double glove box coupled to a vacuum chamber containing both low and high temperature evaporators. For the standard (undoped) OLED's, the hole transport layer (HTL) consisting of 50nm of TPD is deposited by spin coating (8000rpm during 60 sec) and the 40nm of Alq3 were deposited at 2A/sec (organic crucible Radak-I). 150nm of Al were finally evaporated at 5A/s. For the CdSe-doped OLED's, the procedure was the same expect that the QD's were mixed with TPD in toluene before spin coating. During the thermal processing if the film, the QD's are expected to segregate to the surface, and then will be located at the TPD/Alq3 interface. The various layers were imaged by Atomic Force Microscopy (AFM) at each phase of the structure deposition, and we could indeed visualize the segregated QD's above the TPD film. AFM was systematically used to monitor the homogeneity and the thickness of the various films. The impedance of the non-encapsulated films structures were measured in air in the 40-40MHz frequency range, with bias at 0V (non-emitting), 2V (low emission) and 8V (strong emission). The corresponding dielectric spectra were analyzed with the standard Havriliak-Negami (HV) formula, where the conductive term has been subtracted from the data in case of light emission. We have measured a relaxation ranging from 100kHZ for the unbiased structure to 1MHz for 8V (strong emission). Apart from this expected relaxation, we found a second relaxation mechanism around 10 MHz. The origin of this second peak will be discussed. To monitor the optical emission of the OLED's, we have built a specific bench which allows for the quantitative measurement of the emission spectra and the dynamics behavior of the OLED's (raising and falling time). We found that the incorporation of the QD's unfortunately results in the decrease of the light emission but with a favorable modification of the light spectrum (around 700nm).
We report on the power conversion efficiency (PCE) enhancement for organic solar cells (OSCs) based on several approaches. A standard cell composed of an indium tin oxide (ITO) anode, P3HT/ PCBM active layer, PEDOT:PSS hole transport layer and an aluminum cathode is used as a reference. We investigate the effects of the following three modifications. We first incorporate CdSe quantum dots (QDs) in the photo-optically active P3HT/PCBM blend in order to enhance the optical absorption. In opposite to other studies, QDs are not used here to replace the donor material (PCBM), and we always measured an enhanced PCE compared to the standard cell with a QDs:P3HTPCBM volume ratio up to 1:5. As a second modification, NaYF<sub>4</sub>:Yb,Er up conversion (UC) microcrystals are incorporated into a TiO<sub>2-x</sub> sol-gel to form an additional layer used to convert IR photons to blue and green photons. Again, OSCs with UC layer showed an improved PCE compared to the reference cell. The PCE enhancement is both attributed to the IR light absorption and to a better electron transport between the active layer and the cathode due to the electron transport layer capabilities of TiO<sub>2-x</sub>. Finally, MoO<sub>3</sub> layer is used to replace the PEDOT:PSS layer as hole transport layer (HTL). This layer is deposed either by thermal evaporation or by spin coating from a sol-gel solution. We found evaporation better in terms of thickness control and reproducibility. It has been demonstrated that the PEDOT:PSS HTL can be replaced by MoO<sub>3</sub>, and the thickness of this MoO<sub>3</sub> layer strongly affects the PCE of the cell. The maximum PCE was obtained with a thickness of 40nm, and again is better that the reference cell.
Combinatorial CBVD (Chemical Beam Vapor Deposition) is a thin film deposition technology which has the ability to
produce multi-element thin films with large controlled composition spread gradients. If functional characterizations can
be carried out systematically and rapidly on such graded films over full wafers, they enable to identify precisely the best
film composition for a given application, and CBVD then easily allows for the deposition of the optimized film
homogeneously on large wafers. In this article, we demonstrate the efficiency of such a process development based on
the optimization of new Transparent Conductive Oxide thin films (TCO) of few % Nb doped TiO<sub>2</sub>.
We have developed a full wafer metrology instrument which maps the optical thickness and the sheet resistance with a
lateral resolution below 400um. We discuss the performance of various algorithms to extract the optical thickness from
the white light reflectance measurement in the case of very small thickness. The sheet resistance is measured with an
array of four AFM-like conductive cantilevers, allowing accurate sheet resistance (R) measurement where the standard
tungsten four probes destroy porous thin oxide films. Application of these measurements to several Nb doped TiO<sub>2</sub> films
deposited on 4" wafer by CBVD is presented.
We present a systematic investigation of the use of LED as light sources for interference microscopy, in comparison with
more standard halogen illumination. For translation height mode (also known as vertical scanning or low coherence
microscopy), five white LED-based illuminations setup have been tested, including the use of filters to remove the
shoulder in the blue region often encountered in such LED. For the six white light illuminations (five LED plus halogen),
we have measured the irradiance spectra and calculated and measured the corresponding correlograms. The influence of
the combined effect of the illumination spectra and a dispersive phase shift on the calculated height reconstruction is
shown for a center-of-mass algorithm. In phase shift mode, both monochromatic LED and white LED with inteference
filters have been used. Blue LED illumination improves the lateral resolution compared to red illumination, a task which
can be done with halogen lamp only with very reflecting sample due to its low power in the blue wavelengths. All
measurements have been performed with our home-made interference microscope, which is described in Proc. SPIE
We show the integration of a home-made interference optical microscope (IOM) with an Atomic force microscope, as well as the combination of IOM with a nanoindentor. Such combined instruments have many applications in the characterisation of MEMS/NEMS. As an illustrative example, we have used a MEMS accelerometer with capacitive read-out. Surface topography and defects have been measured with an IOM/AFM setup, as well as the bending and the torsion of the inertial mass while a calibrated force is applied with the nanoindentor probe on an off-axis location of the inertial mass.