New approach for analyzing the vertical structure of polymer thin films based on surface-enhanced Raman scattering

We report on a new approach for measuring the chemical composition of the 20 nanometers at the top or bottom of a polymer film. This approach is based on a variation of the surface enhanced Raman scattering effect with laser illumination through a thin gold layer (∼4 nm). We show that the introduction of the thin gold layer has little or no effect on the morphology of the film that is spin coated on top of it. We demonstrate that this technique has better than 20 nanometer vertical resolution by studying bilayers of polyfluorines with varying thicknesses and by showing the existence of top and bottom wetting layers in a polymer blend of the same polymers. We also show that the top wetting layer is thinner than the bottom one. The difference in thicknesses explains how a solar cell with an electron blocking layer at the cathode works

Organic solar cells defects detection by means of an elliptical basis neural network and a new feature extraction technique

The study proposed in this paper devises to develop a new methodology based on elliptical basisneural network (EBNN) and on a new feature extraction technique in order to recognize theorganic solar cells (OSCs) defects. The feature extraction procedure has been obtained by usingthe co-occurrence matrices and the SVD decomposition applied to atomic microscope forceimagery. The polymer-based OSCs used for this work have been produced at the optoelectronicorganic semiconductor devices laboratory at Ben Gurion University of the Negev. The testsperformed show that with our approach it is possible to obtain a correct classification percentageof 95.4% proving that the proposed feature extraction technique based on the co-occurrenceMatrix and the SVD decomposition is very effective in the detection of different types of OSC surface defects

Finite Element Numeric Simulation of Organic Solar Cells with Gold Thin Film

In this paper, we have explored the potential of organic solar cells with gold layers, simulating different geometries and comparing them with the experimental data obtained from the devices produced at the “optoelectronic organic devices laboratory at Ben Gurion University of the Negev, Israel.” Thin-film heterojunction solar devices are analyzed using a basic chemical technology of GLASS/ITO/PEDOT,PSS/P3HT, PCBM, and another type of nanostructure where the gold layer is added. A standard device is realized on top of a transparent substrate such as glass or flexible polymer Polyethylene Terephthalate (PET). The first layer is the anode, which is made of conductive material and is also transparent. In our case, the very common material Indium-Tin-Oxide (ITO) is used. To facilitate the transition between the active layer and the anode, an intermediate layer is introduced. Hole Transport Layer (HTL) 's high hole mobility allows holes to move towards the anode instead of the cathode. On top of these layers the organic active layer is constituted by a blend of two organic materials configuring a multiple junction morphology (Bulk Heterojunction or BHJ). In our case, two commonly organic materials [6,6]-Phenyl C61 Butyric acid Methyl ester and Poly(3-Hexylthiophene-2,5-diyl) (PCBM:P3HT) are used. The cathode on top organic active layer is made of highly conductive opaque metal, mostly Aluminum (Al). The finite-element method has been used to compute the electromagnetic field distributions. The results show that the model with the gold layer increases the electrical performance of organic solar cells

New Approach for Analyzing the Vertical Structure of Polymer Thin Films Based on Surface-Enhanced Raman Scattering

We report on a new approach for measuring the chemical composition of the 20 nanometers at the top or bottom of a polymer film. This approach is based on a variation of the surface enhanced Raman scattering effect with laser illumination through a thin gold layer (∼4 nm). We show that the introduction of the thin gold layer has little or no effect on the morphology of the film that is spin coated on top of it. We demonstrate that this technique has better than 20 nanometer vertical resolution by studying bilayers of polyfluorines with varying thicknesses and by showing the existence of top and bottom wetting layers in a polymer blend of the same polymers. We also show that the top wetting layer is thinner than the bottom one. The difference in thicknesses explains how a solar cell with an electron blocking layer at the cathode works

Optimizing the Organic Solar Cell Manufacturing Process by Means of AFM Measurements and Neural Networks

In this paper we devise a neural-network-based model to improve the production workflow of organic solar cells (OSCs). The investigated neural model is used to reckon the relation between the OSC’s generated power and several device’s properties such as the geometrical parameters and the active layers thicknesses. Such measurements were collected during an experimental campaign conducted on 80 devices. The collected data suggest that the maximum generated power depends on the active layer thickness. The mathematical model of such a relation has been determined by using a feedforward neural network (FFNN) architecture as a universal function approximator. The performed simulations show good agreement between simulated and experimental data with an overall error of about 9%. The obtained results demonstrate that the use of a neural model can be useful to improve the OSC manufacturing processes

The Effect of Bulky Substituents on Two π-Conjugated Mesogenic Fluorophores. Their Organic Polymers and Zinc-Bridged Luminescent Networks

From a dicyano-phenylenevinylene (PV) and an azobenzene (AB) skeleton, two new symmetrical salen dyes were obtained. Terminal bulky substituents able to reduce intermolecular interactions and flexible tails to guarantee solubility were added to the fluorogenic cores. Photochemical performances were investigated on the small molecules in solution, as neat crystals and as dopants in polymeric matrixes. High fluorescence quantum yield in the orange-red region was observed for the brightest emissive films (88% yield). The spectra of absorption and fluorescence were predicted by Density Functional Theory (DFT) calculations. The predicted energy levels of the frontier orbitals are in good agreement with voltammetry and molecular spectroscopy measures. Employing the two dyes as dopants of a nematic polymer led to remarkable orange or yellow luminescence, which dramatically decreases in on-off switch mode after liquid crystal (LC) order was lost. The fluorogenic cores were also embedded in organic polymers and self-assembly zinc coordination networks to transfer the emission properties to a macro-system. The final polymers emit from red to yellow both in solution and in the solid state and their photoluminescence (PL) performance are, in some cases, enhanced when compared to the fluorogenic cores

Microscopic Investigation of Degradation Processes in a Polyfluorene Blend by Near-Field Scanning Optical Microscopy

We have studied the degradation of the photoluminescence (PL) of a phase-separated film of a polyfluorene blend, F8BT/PFO, on the submicron length scale using near-field scanning optical microscopy, visualizing the PL of blend compositions that do not exist macroscopically in equilibrium. In the initial scans, the topography and the PL were anticorrelated, as the emission was dominated by the PFO-rich phase. This behavior changed at longer illumination times, where the emission was dominated by the F8BT-rich phase; i.e., the topography and PL were correlated. Using macroscopic investigation of the mechanisms that govern the PL, we could explain the time dependence of the PL spatial distribution: while the degradation of F8BT was driven by photobleaching, both faster absorption degradation and photobleaching processes dominate the degradation of PFO. In addition, we found that energy transfer does not protect the PFO from degradation and does not improve its resistance to oxidation