Cu(In1-x,Gax)S2 was studied using photoreflectance spectroscopy. In this study, efforts are devoted to optimizing PR set-up for measuring CIGS grown by electrodeposition: issues such as photoluminescence perturbation, high roughness and scattering are addressed. Dual frequency photoreflectance, where both probe and pump beams are modulated, is proposed here to over come the poor signal to noise ratio. Considering the low electric field regime, material parameters are extracted by employing the third derivative functional form of dielectric functions to fit data. The reliability of the technique is finally tested by measuring PR spectra on a specific 15 x 15 cm2 wafer and explanations of PR line-shape evolution on this wafer are discussed.
We present here some of the last results of the EUROPEAN project ALPINE. We present both the development of an
adjustable fibre laser pulse source and scribing results on CdTe and CIGS solar cells. The scribing tests were performed
at three different pulse durations: 400 fs, 8 ps and 250 ps. The results obtained with 250 ps are already very promising
for P3 steps in both CdTe and CIGS solar cells. In both cases the results were validated electrically.
In the case of P3 scribing for CIGS solar cells, shunt resistances as high as 125 kΩ.cm were obtained. Isolation
resistances were higher than 1 MΩ.cm. The processing speed was 2 m/s.
The ALPINE project is developing innovative fiber lasers for the scribing of new thin film photovoltaic modules with the
aims to push forward the European research and development of fiber laser systems and solar energy exploitation. The
fiber lasers will be based on photonic crystal fibers, which are characterized by unusual and interesting light guiding
properties exploited to deliver high power with excellent beam quality and high resonator stability and efficiency, and
will be applied to substitute mechanical scribing steps in the photovoltaic module production. In addition, new
photovoltaic thin film technologies is applied, which is based on cadmium telluride and copper indium diselenide
materials. With a potential conversion efficiency just below that of crystalline silicon, these new material approaches are
ready to enter the market with low manufacturing costs for immediate economic or environment impact.
Surface enhanced second harmonic generation experiments on supramolecules: macrocycles, catenanes and rotaxanes, monolayers and multilayers deposited by vacuum evaporation on silver layers are reported and described. The measurements show that the molecules are ordered in thin films. The highest order is observed in the case of macrocycles and the lowest in thin films of fumaramide  rotaxanes. Also a better ordering is observed in the case of monolayers. The observed second harmonic generation activity is interpreted in terms of electric field induced second harmonic generation. The electric field contributing to SHG signal is created by silver atoms on the surface of silver layers. The measured second order NLO susceptibilities for a fumaramide  rotaxane is compared with that obtained by considering only EFISH contribution to SHG intensities. The electric filed on the surface of silver layer is calculated using TINKER molecular mechanics/dynamics software and the Embedded Atom model. An excellent agreement is observed between the calculated and the measured SHG susceptibilities.
Linear and nonlinear optical properties of newly synthesized amide based rotaxane films are investigated. The dispersion curves of refractive indices have been characterized. A relatively large anisotropy of refractive indices is observed. The vacuum deposited thin film can be poled by a static electric field. This fact shows some degree of freedom for the mobility of macrocycle with respect to the thread. The induced d33 susceptibility after static electric field polarization at (lambda) =1.064micrometers is 0.57 pm/V and 3.43 pm/V for rotaxane 1 and 2 respectively. Kinetics of poling and relaxation at different temperatures was studied by in situ SHG technique. From the poling kinetics the characteristic response times of the system were evaluated. Third harmonic generation was measured at 1.064micrometers and 1.907micrometers fundamental wavelengths. The electronic part of the third order NLO susceptibility (chi) (3) (-3(omega) ;(omega) ,(omega) ,(omega) ) was found to be (6.4+/- 0.2)*10-13esu and (4.1+/- 0.8)*10-13esu at 1.604micrometers and (6.9+/- 0.4)*10-13esu and (4.2+/- 0.3)*10-13esu at 1.907micrometers for 1 and 2 respectively. Upon UV irradiation a clipping movement induced by a trans-cis isomerization process has been identified.
An alternating electric field is used to address the structure of two hydrogen bond-assembled rotaxanes and their interlocked molecular fragments by recording the electro- optic Kerr effect. Both rotaxanes consist of two nitrogen hydrogen bond acceptors 1 and a fumaramide unit 2 in the thread. The macrocycle is common. The experimentally determined Kerr constant as a function of the frequency of the applied AC field shows a resonance at 50Hz for both rotaxanes. This resonance is absent for the corresponding uninterlocked components or the solvent itself. A second resonance, around 80Hz was found for the fumaramide rotaxane but not for the nitrone one. The resonances have been shown to be field strength and temperature dependent, shifting to lower values with increasing the applied voltage and or temperature. Nuclear Magnetic Resonance (NMR) spectrometry shows that the only possible process is a 180 degree(s) circumrotation of the macrocycle around the thread. The rate of the macrocycle circumrotation measured by NMR is in the regime of that seen for the Kerr effect resonance. Theoretical simulations of the submolecular motion show that in 1 the macrocycle ring rotates smoothly with little further perturbations. In comparison 2 presents a more complicated picture where several processes are coupled.
Linear and nonlinear optical properties of thin films of polyvinyl carbazol (PVK) and its derivatives were studied by UV-VIS spectroscopy and by harmonic generation techniques. Refractive index and its dispersion was measured for PVK and functionalized PVK by m-lines technique. PVK is an interesting polymer because of its high glass transition temperature and photoconducting properties. Functionalized with coumarine may be used for LED's applications and shows also interesting second order NLO properties when poled. The poled polymers may be reversibly depoled with UV light. However, such a process, whose kinetics depends on temperature, leads to a decrease of second-order NLO process. The third-order NLO susceptibility X(3)(- 3(omega) ;(omega) ,(omega) ,(omega) ) is about three times larger for modified PVK and comparable to that found in polysilanes with a larger transparency range.
The bulk growth of periodic poled lithium niobate (PPLN) is made by the off-centered Czochralski technique adding an impurity to the melt. The periodic domain structures are obtained with different impurities such as Er, Yb, Nd, Cr, Fe and Y. The impurity distribution along the bulk PPLN crystals has been studied to understand the formation mechanism of the periodic domain structure. The distribution coefficient of the impurities, the temperature fields and the shape of the solid-liquid interface have been found to play a key role in the PPLN formation. The cooling rate and other growth conditions control the size of the areas where the periodic domain structure appears. It has been found that independently of the impurity added to the melt the dopant concentration is constant along the periodical domain structure, while it has been observed that exists a periodical variation of the Nb concentration which is related one to one with the periodical domain structure.
Second harmonic generation in Lithium Niobate (LN) thin films has been widely studied. This interest is extended to waveguides obtained by the Liquid Phase Epitaxy (LPE) technique due to the high perfection and crystallinity of the films. However the incorporation of vanadium into the film due to the growth technique is still a problem because of the absorption band of this ion in the visible zone of the spectra. In this work the LN films are obtained by the LPE technique on pure LN singledomain substrates in the horizontal LPE geometry. Several temperatures have been used in order to obtain the best crystalline quality. The starting flux used was LiVO3 80 mol%, with a Li rich melt of LiNbO3.