Rodrigo Martins

This work refers to the fabrication of hybrid solar cells based on porous silicon (PS) filled with copper phthalocyanine (CuPc) to form GZO/CuPc-PS/Si/Al structure. We used n-type Si since photoinduced charge transfer from CuPc to Si is observed only for n-type Si. The characteristic 100% peak at 6.8°2θ from XRD confirms that the CuPc coating on PS exists in α-CuPc polymorph. The systematic increase in FWHM of XRD peak at 69.1°2θ and red-shift of LO phonon Raman spectra indicate a progressive reduction of Si nanocrystallites size with increasing etching time and the estimated size agrees well with atomic force microscopic images. The FTIR results confirm the formation of α-CuPc polymorph and it is also corroborated well with XRD and Raman results. © 2008.

This work presents a fast method to determine qualitatively the uniformity and the thickness of transparent or semitransparent thin films in the visible to near-infrared region. The method proposed is based on the information recorded by a colour scanner in the form of coloured regions, due to the constructive interferences caused by multibeam wavelength light sources as function of the film thickness and refractive index. The method is well applied in transparent films, where the uniformity cannot be seen by visual inspection. This paper shows that the results obtained for ZrO2 films are satisfactory enabling the application of this technique to determine the films uniformity in fast and cheap way.

Flexible and large area (5 mm × 80 mm with an active length of 70 mm) position-sensitive detectors (PSDs) deposited onto polymeric substrates (polyimide - Kapton VN) have been fabricated. The optimized structure presented is based on a heterojunction of amorphous silicon (a-Si: H)/ZnO: Al. The sensors were characterized by spectral response, photocurrent dependence as a function of light intensity, and position detection measurements. The set of data obtained on one-dimensional PSDs based on the heterojunction show excellent performances with a maximum spectral response of 0.12 A/W at 500 nm and a nonlinearity of ±10% over 70-mm length. The produced sensors present a nonlinearity higher than those ones produced on glass substrates, due to the different thermal coefficients exhibited by the polymer and the a-Si: H film. In order to prove this behavior, it was measured the defect density obtained by the constant photocurrent method on a-Si: H thin films deposited on polymeric substrates and bent with different radii of curvature. © 2005 IEEE.

Large area thin film position sensitive detectors based on amorphous silicon technology have been prepared on polyimide substrates using the conventional plasma-enhanced chemical vapour deposition. The sensors have been characterized by spectral response, light intensity dependence and linearity measurements in a bent state in order to evaluate the properties in real working conditions. The obtained one-dimensional (1D) position sensors with 10 mm width and 20 mm length present a non-linearity of ±1% which are comparable to the ones produced on glass substrates.

This work describes the fabrication and characterization of an improved version of large area (5mm×80mm with an active length of 70mm) flexible position sensitive detectors deposited onto polymeric substrates (polyimide-Kapton® VN). The new configuration presented by the sensor is based on a heterostructure of a-Si:H/ZnO:Al. The sensors were characterized by spectral response, photocurrent dependence as a function of light intensity and position detection measurements. The set of data obtained on one-dimensional position sensitive detectors based on the heterostructure show excellent performances with a maximum spectral response of 0.12A/W at 500nm and a non-linearity of ±10% over 70mm length. The produced sensors present a non-linearity higher than those ones produced on glass substrates, due to the different thermal coefficients exhibited by the polymer and the amorphous silicon film. In order to prove this behaviour, it was measured the defect density obtained by the constant photocurrent method on amorphous silicon deposited on polymeric substrates bended with different radius of curvature. © 2004 Elsevier B.V. All rights reserved.

Reported herein is a nonvolatile n-type floating gate memory paper field-effect transistor, emphasizing the role of the paper structure and properties on the device performance recorded such as in the high capacitance per unit area at low frequencies (>2.5 μFcm-2) and so on the set of high charge retention times achieved (>16000 hours). The device was built via the hybrid integration of natural cellulose fibers, which act simultaneously as substrate and gate dielectric, using amorphous indium zinc and gallium indium zinc oxides respectively for the gate electrode and channel layer. This was complemented by the use of continuous patterned metal layers as source/drain electrodes. © 2010 Copyright SPIE - The International Society for Optical Engineering.

A Linear array Thin Film Position Sensitive Detector (LTFPSD) based on hydrogenated amorphous silicon (a-Si:H) is proposed for the first time, taking advantage of the optical properties presented by a-Si:H devices we have developed a LTFPSD with 128 integrated elements able to be used in 3D inspections/measurements. Each element consists on a 1D LTFPSD, based on a p.i.n. diode produced in a conventional PECVD system, where the doped layers are coated with thin resistive layers to establish the required device equipotentials. By proper incorporation of the LTFPSD into an optical inspection camera it will be possible to acquire information about an object/surface, through the optical cross- section method. The main advantages of this system, when compared with the conventional CCDs, are the low complexity of hardware and software used and that the information can be continuously processed (analogue detection).

This work presents the main static and dynamic performances showed by one dimensional thin film position sensitive detectors (1D TFPSD), based on a-Si:H technology, with a size of 80 mm × 5 mm. The results obtained show that the TFPSD is able to respond to light powers as low as 2μ W/cm2, presenting a detection accuracy, linearity and response frequency better than 10 μm, 2% and 2 KHz, respectively. These results are quite promising regarding the application of these sensors to a wide variety of optical inspection systems where continuous quality control is required.

The special Professor Walter E. Spear commemoration issue of the Philosophical Magazine, published in October 2009, contains papers which cover the numerous relevant issues, driven by commercial applications, primarily solar energy and displays. Kocka reviews the complex microstructure of crystallites embedded in the amorphous silicon tissue, the transport mechanism is determined by the conductive grains and influenced by the passivation through H at the grain boundaries. Hugger and co-researchers report on transient photocapacitance spectroscopy and drive-level capacitance profiling as a way of elucidating the fundamental electronic properties of hydrogenated ncSi. Tawada recounts the history of a-Si:H pin heterojunction solar cells, emphasizing the role of the p-type silicon carbide layer in the improvement of the device. Schubert and colleagues focus their work on the production of flexible PV modules with many applications in the architectural arena or integrated into clothing.

Doped a/μc-Si:H films were produced in different starting deposition conditions by the hot wire chemical vapor deposition technique. In this paper, we show that by changing the initial onset deposition conditions of the process and maintaining the overall pressure, hydrogen dilution and filament temperature, it is possible to control the compactness of the films. As the films nucleation is the key parameter to produce compact films, we show that starting the process with hydrogen and progressively introducing the process gas enhances the compactness and improve the electrical properties of the films produced. © 2002 Elsevier Science B.V. All rights reserved.

The possibility of fabricating high-mobility ZnO thin-film transistors (ZnO-TFT) at room temperature by rf magnetron sputtering was discussed. It was found that the films were nanocrystalline with a hexagonal structure and exhibited a preferred orientation with the c-axis perpendicular to the substrate. The undoped ZnO films exhibited improved crystallinity fraction of the nanocrystals and low oxygen vacancies. Analysis shows that the exposure of the ZnO-TFTs to the ambient light has no effect on the current voltage characteristics.