Electrical conductivity in a-Si:H:Cl films

The temperature dependence of the electrical conductivity was investigated in chlorinated and hydrogenated amorphous silicon films (a-Si:H:Cl) deposited by glow discharge in the SiCl₄SiH₄ mixtures. The influence of chlorine on the different transport processes is determined according to the investigated temperature range. On the base of the experimental results and the speculative considerations regarding the film structure the inference is drawn that chlorination of hydrogenated amorphous silicon causes a decrease in the gap state density and an increase in the structural disorder. It is supposed that a more definite improvement of the electronical properties of glow discharge amorphous silicon could be expected for the relatively low chlorine concentration of about (1.0–2.0)×10²¹ at/cm³.     

Destination: Perfection

The objectives of the perfect power project include: 1) the achievement of system-wide perfect power and demonstration of its technological viability; 2) 50% peak demand reduction capability via on-site generation when called upon by ComEd/PJM; 3) deferral of ComEd planned substation upgrades due to the demand reduction achieved; 4) demonstration of the economic value of perfect power, specifically the avoidance of outage costs and the introduction of significant savings and revenue from providing ancillary services; and 5) a design that can be replicated to any municipality-sized system where customers can participate in electric power market opportunities. In addition, the IIT team seeks to fulfill the mission of the university as set forth by President John L. Anderson, "IIT will be internationally recognized in distinctive areas of education and research, using as its platform the global city of Chicago, driven by a focus on professional and technology oriented education, and based on a culture of innovation that embraces bold and transformational ideas." Transforming the IIT power delivery infrastructure to achieve perfect power is a bold idea that will require a never-ending series of innovations. We have embraced the vision of the GEI and we look forward to sharing our progress with the power and energy community in the years to come.     

Electrical conductivity in microcrystalline Si:H:Cl films

The dark and photoconductivities of microcrystalline Si films, deposited from SiCl₄ by the cold rf plasma method, have been investigated as a function of total gas pressure and dopant concentration, and have been correlated to the chlorine contents of the films. It was found that deposition pressure affects the electrical conductivity, its activation energy and the type of the films deposited without dopant gases. The chlorine content of the film is dependent on the type and concentration of the dopant gas and is affecting mainly the photoconductivity. The electrical conductivity of the silicon films is strongly dependent on the dopant incorporated in them and can be changed by several orders of magnitude.     

Mission: Reliability

Power system "operating reliability" is at the core of responsibilities that have been entrusted by French law to the Reseau de Transport d'Electricite (RTE), in its capacity as France's transmission system operator (TSO). The Power System Reliability Audit Mission is responsible for two main complementary activities: 1) carrying out power system reliability audits and 2) drafting of a yearly power system reliability report. In this section we present the principles, on which the control of system reliability is based, the procedure for creating the yearly reliability report, the procedure for the elaboration of the reliability audit plan, and the procedures governing the reliability audits.     

A-Si:H buffer in a-SiGe:H solar cells

Profiled a-SiGe:H-buffer layers between the doped and the absorption layers of amorphous silicon germanium (a-SiGe:H) solar cells are routinely used to avoid bandgap discontinuities and high-defect densities at the p/i- and i/n interface. Here, we present a much simpler approach replacing the profiled a-SiGe:H-buffer layers at both interfaces by a-Si:H-buffer layers. It is demonstrated that for a-SiGe:H solar cells (thickness of the E_G=1.5 eV part is 54 nm) these structures yield similar open circuit voltage V_OC and fill factor (FF) compared to the bandgap profiled layer at the same short circuit current density j_SC. The influence of thickness, optical bandgap and position of the buffer layers on the solar cell performance is investigated.     

Light Scattering in Pigmented Coatings:: Experiments and Theory

Small silica particles uniformly coated by a shell of titania, were produced by wet chemical methods. The pigments were dispersed in polymeric binders and were applied as paints to glass substrates. Total reflectance and transmittance were determined by integrating sphere measurements. Luminous and solar reflectance of paints containing the novel pigments were comparable with paints containing commercial titania. The spectral transmittance and reflectance of the paints were modelled by a four-flux radiative transfer theory. Theory and experiment could be brought into good agreement, if it was assumed that the particles were slightly porous. The studied pigments may find applications in sunscreens or in foils for daylighting and radiative cooling.     

Microcrystalline-phase p-type a-Si:O:H windows prepared by Cat-CVD

Different amounts of oxygen, boron-doped hydrogenated amorphous silicon (a-Si:H) and hydrogenated microcrystalline silicon (μc-Si:H) deposition were carried out using catalytic chemical-vapor deposition (Cat-CVD) process. Pure silane (SiH₄), hydrogen (H₂), oxygen (O₂), and diluted diborane (B₂H₆) gases were used at the deposition pressure of 0.1–0.5 Torr. The tungsten catalyst temperature (T_fil) was varied from 1700 to 2100 °C. Sample transmittance measurement shows an optical-band gap (E_gopt) variation from 1.45 to 2.1 eV X-ray diffraction (XRD) spectra have revealed silicon microcrystalline phases for the samples prepared at the temperature greater than T_fil1900 °C. For the used silicon oxide deposition conditions, no strong tungsten filament degradation was observed after a number of sample preparations.     

Consultants'' corner : Training: The key to success in PV

The funny thing about the supply of PV systems, is that unpredictability of where the weakest link in the chain lies. You only spot it when it breaks! Ian Draisey, Dulas, UK provides a perspective on supplying PV systems around the world. From lessons learnt in 20 years of export operations in this field we see that as well as supplying and installing the system, the focus should equally be made on after sales service, training and simplicity of design.     

In-situ Kelvin probe and ellipsometry study of the doping of a-Si : H and a-SiC : H layers:: Correlation with solar cell parameters

To underscore the effects of boron doping on the photovoltaic characteristics of a-Si : H based p–i–n solar cells we used the in-situ Kelvin probe technique to determine the evolution of the contact potential at the SnO₂/p interface in two series of solar cells: one with a p(a-Si : H) layer and another with a p(a-SiC : H) layer plus a buffer a-SiC : H layer. In each series, the flow of diborane was varied between 0.5 and 7 sccm. The in-situ Kelvin probe measurements on thick layers indicate that the doping efficiency is higher in a-Si : H than in a-SiC : H layers. In the case of cells with a p(a-Si : H) layer we observe an optimum in V_oc as a function of the diborane flow rate. Below this optimum the increase in V_oc is correlated to the increase of the contact potential measured by the Kelvin probe. Above the optimum value of the diborane flow, the further increase of the contact potential contrasts with the decrease of V_oc. Moreover, we found that V_oc of the cells with a p(a-SiC : H) is independent of the diborane flow rate. This unexpected behaviour is interpreted in terms of the diffusion of impurities and changes in the p-layer induced by boron atoms; it is supported by secondary-ion mass spectrometry and in-situ spectroscopic ellipsometry measurements.     

Palestine: RE action plan : Moving away from traditional energy resources

Renewable energy resources show great promise in Palestine. Solar, wind, biogas and geothermal energy resources are the main areas where research and pilot projects are being concentrated (2000–2005). More than 95% of Palestinians use solar energy for domestic water heating so renewable energy is something that many people in the country are already very aware. Consequently, use of renewable energy resources presents a strategic goal for the Palestinian energy authority in order to achieve some degree of economic independence. It aims to minimize the dependence on traditional energy resources that are too expensive and politically controlled. Awny Naim and Mohammad R Al-Agha, Palestinian Renewable Energy Society describe the current situation in the region.