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32nd European Photovoltaic Solar Energy Conference and Exhibition; 651-655, In a-Si:H/c-Si heterojunction solar cells the UV absorption of amorphous layers limits the current generation. The use of a more transparent material like a-SiOx:H films is a key to further enhance the efficiency of this kind of cells. At the same time this layer must guarantee high surface passivation of the c-Si wafer to be suitable in high efficiency solar cell manufacturing. As for amorphous silicon, thermal annealing procedures are considered as valuable steps to enhance and stabilize thin film properties, when performed at opportune temperature. In order to avoid damages of the amorphous layer, each cell fabrication step should be carried at temperature lower than the emitter formation one. However, when thermal annealing is applied as one of the early fabrication step, the temperature can be high enough to obtain the best passivation properties. In this work we have analyzed the effect of several thermal treatments different for temperature, duration and surrounding atmosphere on a-SiOx:H/c-Si/a-SiOx:H structure. We have fully characterized the samples with the aid of effective lifetime evaluation and FTIR spectra to correlate the effect of thermal annealing to the a-SiOx:H/c-Si interface.

We design a distributed feedback guided-wave device in liquid crystals, utilizing a simple geometry based on electro-optic molecular reorientation in uniaxial nematics. We numerically test the structure and demonstrate an effective Bragg reflector with voltage-tunable resonance. (C) 2009 Optical Society of America

We propose a versatile guided-wave geometry encompassing electro-optic control for signal routing. A zero-gap directional coupler in liquid crystal can switch between two output states in the guide plane, permitting signal rerouting with modulation voltages as small as 70 mV. In the absence of an applied bias, no guiding-hence no modal output-is provided by the structure. (c) 2005 Optical Society of America.

We demonstrate a compact, low-power and broadband electro-optic switch in a simple waveguide geometry with undoped nematic liquid crystals. We experimentally achieve near infrared switching and signal routing with voltage modulations as low as 0.21V and a device length of 0.16mm. (C) 2005 Optical Society of America.

28th European Photovoltaic Solar Energy Conference and Exhibition; 1971-1975, The photovoltaic characteristics of amorphous/crystalline silicon hetero-junction solar cells are strictly related to the electronic quality of the junction interface. In this paper we investigate the effect hydrogen plasma treatments performed on thin amorphous silicon buffer layer deposited over crystalline silicon surface. In particular we propose the use of surface photovoltage technique as a contact-less tool for the evaluation of the energetic distribution of the state density at amorphous/crystalline silicon interface. The measurement results have been compared with those obtained on the same structure after thermal annealing on the interface. We found that both processes bring to a reduction of the state density of about one order of magnitude, but while the thermal annealing produces a metastable state which goes back to the initial state after just 48 hours, the effect of hydrogen plasma posttreatment results much more stable.

All-optical control of a polymer rectangular waveguide with liquid crystal core is theoretically investigated. Light propagation is established with low input power control, that excites optical nonlinearity due to optically induced reorientational effect.

This paper reports on linear and nonlinear optical properties of channel waveguides made of micromachined SiO2/Si Vgrooves filled with nematic liquid crystal E7. Experiments demonstrate operation of the waveguides in the C-band (1530 - 1565 nm). Molecular reorientation of the NLC, induced either by an applied low frequency electric field or by the electric field of the light itself, changes the LC refractive index distribution then allowing the control of guided light. Design criteria and techniques of channel waveguides for both electro-optical and all-optical switching and modulation will be discussed. Experiments are presented where it is showed that light at 1550 nm, fiber-coupled to the LC waveguide is optically modulated by an optical beam with an input power below 25 mW. All-optical switching of a signal at 1510 nm with a contrast over 10 dB is also demonstrated by using a copropagating control signal at 1560 nm. A model of the waveguide is also presented able to explain linear and nonlinear experimental results.

The optical nonlinear transmission of a channel waveguide with E7 liquid crystal core infiltrated in a SiO2/Si V-groove is experimentally and theoretically investigated. Low input power excites optical nonlinearity due to optically induced reorientational effect.