Papers by Keyword: Electrical Activity

Abstract: In this paper we combine LBIC and EL measurements of commercially multi-crystalline silicon solar cells, in order to obtain detailed information about the electrical activity around defect areas. This integrated analysis is suitable for the study of different crystal defects at both micrometric and full wafer scale. In particular, the electrical activity of some defect areas is studied in detail by means of highly spatially-resolved LBIC maps, showing important differences in their behaviours. A discussion about the origin of these differences is presented.

Abstract: A simple and versatile method has been invented to fabricate conducting polymer hydrogels via supramolecular self-assembly between polymers and multivalent cations. As-prepared hydrogels composed of poly(3,4-ethylenedioxythiophene) and poly(styrenesulfonate) (PEDOT-PSS) exhibit expanded-coil conformation in polymer chains, phase-separate at nanometer scale, possess controllable microstructure, and is responsive to external stimulus. The conducting PEDOT-PSS hydrogels have then been introduced into multiple-network hydrogels to obtain composite hydrogels combining enhanced mechanical strength and excellent electrical activity. Triple-network (TN) and special double-network (sDN) hydrogels, containing poly(acrylic acid) (PAA) and poly(acrylamide) (PAAm) as the matrix respectively, are successfully prepared. Finally, PEDOT-PSS hydrogels with self-strengthening function are directly fabricated via a one-step process under optimized conditions. The strengthening mechanisms for each kind of hydrogels are proposed, and the applicability in electrosensors, supercapacitors and electromechanical actuators are briefly demonstrated.

Abstract: Germanium is an attractive model system for studying the crystallization mechanism and optimization of the growth processes in photovoltaics. In comparison to Si it has a lower melting point and that is why its usage is cost effective. The main aim of our work was to verify the similarities in the growth related defect formation between Ge and Si. We apply standard Si characterization methods to poly and VGF-grown n-type Ge. Room temperature and 80 K EBIC measurements were done to reveal the defect structure. Photoluminescence spectra were used to characterize the optical properties as for instance the Ge band-to-band or defect originated transitions. Additionally, photoluminescence and cathodoluminescence maps were preformed to reveal the defect distribution/activity, too, by using the direct Ge band-to-band transition.

Abstract: We report on the optical and mechanical properties of Si3N4 inclusions, formed in the upper part of mc-Si blocks during the crystallization process. Those inclusions usually appear as crystalline hexagonal tubes or rods. Here we show that in many cases the Si3N4 inclusions contain crystalline Si in their core. The presence of the Si phase in the centre was proven by means of cathodoluminescence spectroscopy and imaging, electron beam induced current measurements and Raman spectroscopy. The crystalline Si3N4 phase was identified as β-Si3N4. Residual stress was revealed at the particles. While the stress is compressive in the Si material surrounding the Si3N4 particles tensile stress is found in the Si core. We assume that the stress is formed during cool down of the Si block and is a consequence of the larger thermal expansion coefficient of Si in comparison to that of β-Si3N4. Iron assisted nitridation of Si at temperatures below 1400 °C is considered a possible mechanism of Si3N4 formation.

Abstract: A new approach to grain boundary engineering for photovoltaic polysilicon has been attempted using a new processing method of unidirectional and rotational solidification from the melt, in order to control the grain boundary microstructure and to produce desirable bulk electrical properties. The effect of grain boundary microstructure on bulk electrical properties of polysilicon can be more precisely evaluated by introducing a new parameter “directional grain boundary density (DGBD)” in connection with basic knowledge of structure-dependent grain boundary electrical properties, the grain boundary character distribution (GBCD) and grain boundary geometrical configuration which can be experimentally determined by Orientation Imaging Microscopy (OIM). We report the usefulness of this approach to development of high performance polysilicon.