Rhythmic pineal melatonin biosynthesis develops in chick embryos incubated under a light (L)-dark (D) cycle of polychromatic white light. The spectral sensitivity of the embryonic pineal gland is not known and was investigated in this study. Broiler breeder eggs (Ross 308, n=450) were incubated under white, red, green or blue light under the 12L : 12D cycle. Melatonin was measured in extracts of pineal glands by radioimmunoassay. The daily rhythm of pineal melatonin levels in 20-day-old chick embryos was confirmed during the final stages of embryonic life under all four wavelengths of light with expected higher concentrations during dark- than light-times. The highest pineal melatonin levels were determined in chick embryos incubated under red and white light and lower levels under green light. The incubation under blue light resulted in the lowest melatonin biosynthesis. Pineal melatonin concentrations increased substantially on post-hatching day two compared with pre-hatching levels and we did not find differences between birds incubated and kept in either white or green light. Our results demonstrate a selective sensitivity of the chick embryo pineal gland to different wavelengths of light. Rhythmic melatonin production is suggested as a possible mechanism, which transfers information about the quality of ambient light to the developing avian embryo.

Photovoltaic (PV) systems are progressively used for decentralized electricity generation. To obtain the maximum yield from such systems, optimisation of all components is essential. In this contribution, we provide a comprehensive modelling and sizing of PV systems for any location. Three applications are here presented providing real time monitoring of PV potential, accurate prediction of yield taking into account thermodynamic temperature effects, optimization of modules orientation addressing the effects of shading and efficient sizing of inverter for a higher yield output. When combined, these models can accurately predict the real time performance of any PV system.

For increasing the awareness of photovoltaic (PV) conversion and its consumer developments, a PV-powered infotainment spot (information + entertainment) has been recently designed to be used in the campus of Delft University of Technology. This demonstrator provides information to people on campus via a rugged touchscreen that is powered only by solar energy. In this PV system, a 90-W rated flexible CIGS module was deployed as market alternative to rigid c-Si modules. A methodology to accurately estimate the irradiance on a curved plane was developed. Taking into account temperature, irradiance and shading effects, the energy production of the PV module was estimated to be 62 kWh/year. On the other hand, the load should exhibit an energy consumption of 19.3 kWh/year. By means of a 12-V DC mini grid, the excess energy was thus stored in a 120 Ah battery regulated via charge controller or made directly available with two ad-hoc USB ports for smartphone battery recharging. The realized prototype of the infotainment spot is potentially a completely autonomous small-scale PV system with zero loss of load probability.

We recently developed a scattering model based on the scalar scattering theory. In this contribution we present how we used the scattering model to investigate interface textures with optimized scattering properties. We used the simulated annealing algorithm to find optimized surface textures and applied the ASA device simulator to evaluate the influence of these optimized textures on the performance of thin film silicon solar cells. We found that the lateral feature size of the textures is crucial for efficient scattering of the incident light.

Three-dimensional (3-D) optical modeling based on Finite Element Method of single, double, and triple junction thin-film silicon solar cells is presented. The combination of front periodic gratings with optimal geometrical parameters and rear ZnO/Ag reflector constitutes an efficient light trapping scheme for solar cells in superstrate (pin) configuration. The application of optimized trapezoidal 1-D and 2-D gratings resulted in 25.5% (1-D case) and 32.5% (2-D case) increase in photo-current density with respect to the flat solar cell. The application of inverted pyramidal 2-D gratings in double and triple junction silicon solar cells with very thin absorber layers resulted in a photo-current density > 11 mA/cm2 and > 9 mA/cm2, respectively.

Design of one-dimensional periodic gratings is investigated for enhancing the light absorption in thin-film silicon solar cells due to scattering at rough interfaces that are introduced into solar cells by the gratings. A rigorous full-wave analysis is carried out in order to determine the optical properties of amorphous and microcrystalline silicon solar cells in PIN and NIP configurations, respectively. Optimal geometrical parameters of 1-D gratings for maximizing photocurrent density in thin-film silicon solar cells are determined.

Modulated surface-textured substrates for thin-film silicon solar cells exhibiting high haze in a broad range of wavelengths were fabricated. Glass substrates coated with different thicknesses of a sacrificial layer were wet-etched allowing the manipulation of the surface morphology with surface roughness ranging from 200 nm up to 1000 nm. Subsequently, zinc-oxide layers were sputtered and then wet-etched constituting the final modulated textures. The morphological analysis of the substrates demonstrated the surface modulation, and the optical analysis revealed broad angle intensity distributions and high hazes. A small anti-reflective effect with respect to untreated glass was found for etched glass samples. The performance of solar cells on high-haze substrates was evaluated. The solar cells outperformed the reference cell fabricated on a randomly-textured zinc-oxide-coated flat glass. The trend in the efficiency resembled the increased surface roughness and the anti-reflective effect was confirmed also in solar cell devices.

In the recent years more and more theoretical and experimental evidence have been found that the hydrogen bonded to silicon in dense hydrogenated amorphous silicon (a-Si:H) predominantly resides in hydrogenated divacancies. In this contribution we will philosophize about the option that the small fraction of divacancies, missing at least one of its bonded hydrogen, may correspond to some of the native and metastable defect states of a-Si:H. We will discuss that such defect entities are an interesting basis for new and alternative views on the origin of the SWE.

This article focuses on the modeling and simulation of thin-film silicon solar cells to obtain increased efficiency. Computer simulations were used to study the performance limits of tandem and triple-junction, silicon-based solar cells. For the analysis, the optical simulator SunShine, which was developed at Ljubljana University, and the optoelectrical simulator ASA, which was developed at Delft University of Technology, were used. After calibration with realistic optical and electrical parameters, we used these simulators to study the scattering properties required, the absorption in nonactive layers, antireflective coatings, and the crucial role of the wavelength-selective intermediate reflector on the performance of the solar cells. Careful current matching was carried out to explore whether a high photocurrent [i.e., more than 15 mA/cm2 for a tandem hydrogenated amorphous silicon (a-Si:H)/hydrogenated microcrystalline silicon (μc-Si:H) solar cell and 11 mA/cm2 for a triple-junction a-Si:H/amorphous silicon germanium (a-SiGe:H)/μc-Si:H solar cell] could be obtained. In simulations, the extraction of the charge carriers, the open-circuit voltage, and the fill factor of these solar cells were improved by optimizing the electrical properties of the layers and the interfaces: a p-doped, a-SiC layer with a larger band gap (EG > 2 eV) and buffer layers at p/i interfaces were used. Simulations demonstrated that a-Si:H/μc-Si:H solar cells could be obtained with a conversion efficiency of 15% or higher, and triple-junction a-Si:H/a-SiGe:H/μc-Si:H solar cells with an efficiency of 17%.

In order to improve light trapping in thin-film silicon solar cells two novel approaches are investigated in this article: angle-selective management of light scattering inside the solar cell and wavelength-selective manipulation of high reflectance or transmittance of light. Diffraction gratings are analyzed as a representative of the first approach. Haze and angular distribution function of scattered (diffracted) light in reflection are measured for aluminum-based rectangular periodic gratings with different period and height of the rectangles. High haze values in specific wavelength region and scattering angles of the investigated gratings measured in air and water agree very well with the theoretical predictions. Considering the actual optical situation in microcrystalline silicon solar cells, optimal period and height of the rectangular gratings applied as a back reflector are calculated for obtaining the total reflection at the front interfaces. In the frame of the second approach, photonic-crystal-like structures are introduced. By means of optical simulations photonic-crystal-like structures are investigated for two possible applications: an intermediate reflector in a micromorph silicon solar cell with wavelength-selective reflectivity and a dielectric back reflector with a high reflectance in the long-wavelength region. The photonic crystal structure consisting of sequences of n-doped amorphous silicon and ZnO layers is designed for the efficient intermediate reflector. For the back reflector with a high reflectance the structures with intrinsic amorphous silicon, SiO2, MgF2 and TiO2 are proposed.

Geographic information systems (GIS), their fundamental components and technologies are described. GIS is a computer-based system enabling the storage, integration, query, display and analysis of data using information on data location. Further, remote sensing (RS) methods and their application in landscape characterization are described. Landscape pattern analysis, combined with statistical analysis, allows the determination of landscape predictors of disease risk. This makes RS/GIS a powerful set of tools for disease surveillance, enabling the prediction of potential disease outbreaks and targeting intervention programs. The ‘pre-GIS era’ is briefly described including the early mapping of tick distribution, analyses and the display of biogeographical and medical data. The theory of natural focality of diseases (NFD) is explained and its significance in tick-borne diseases (TBD) research is discussed. Many problems of tick ecology and TBD epidemiology and epizootology have been addressed by means of GIS and examples of these studies are presented and discussed.

The evolution of the programmed defect-state distributions in intrinsic hydrogenated amorphous silicon (a-Si:H) due to light soaking was qualitatively determined from charge deep-level transient spectroscopy. The defect-state distribution in a-Si:H was programmed by applying a particular bias voltage on the metal-oxide-semiconductor structure while annealing the structure above the equilibration temperature. The programmed distributions simulate defect-state distributions in different parts of an actual a-Si:H solar cell, particularly in the intrinsic regions close to the p/i and i/n interfaces.

The defect-state distribution in the bulk of the intrinsic layer is characterized by comparable contributions from the positively charged defect states above midgap, Dh, neutral states, Dz, and negatively charged states below midgap, De. In the programmedp-type (n-type) defect-state distribution there is an excess of the Dh (De) states. Light exposure modifies the p-type distribution that evolves to a broad distribution of states with a maximum around midgap. This distribution is dominated by Dz states with substantial contributions from Dh and De states. In case of n-type distribution light soaking only slightly influences the distribution by removing a part of the Dh states and by a small increase of Dz and De states.

Computer simulations of single-junction hydrogenated amorphous silicon (a-Si:H) solar cells with different thickness of the intrinsic layer were carried out in order to study the role of charge gap states in their light-induced degradation. It is demonstrated that it is the decrease of positively charged states above midgap, Dh, and the increase of neutral states around midgap,Dz, and negatively charged states below midgap, De in the intrinsic layer that result in a drop of performance of the solar cells due to light soaking. These changes in the gap states are in accordance with our recent experimental results from the charge deep-level transient spectroscopy on undoped a-Si:H. The experimentally observed changes in the dark and illuminated J-V curves and spectral response could not be simulated with the same set of input parameters by only increasing the defect-state density in the intrinsic layer.

The charge deep-level transient spectroscopy (Q-DLTS) experiments on undoped hydrogenated amorphous silicon (a-Si:H) demonstrate that during light soaking the states in the upper part of the gap disappear, while additional states around and below midgap are created. Since no direct correlation is observed in light-induced changes of the three groups of states that we identify from the Q-DLTS signal, we believe that we deal with three different types of defects. Positively charged states above midgap are related to a complex formed by a hydrogen molecule and a dangling bond. Negatively charged states below midgap are attributed to floating bonds. Various trends in the evolution of dark conductivity due to light soaking indicate that the kinetics of light-induced changes of the three gap-state components depend on their initial energy distributions and on the spectrum and intensity of light during exposure.

With an Expanding Thermal Plasma Chemical Vapor Deposition system (ETP-CVD), solar grade amorphous silicon (a-Si:H) can be deposited at high deposition rate (> 2 nm/s). We think that during the first stage of deposition, a material is grown with a higher defect density than the rest of the bulk creating a defect-rich layer (DRL). Therefore we analyzed, by the means of simulations, the influence of the position of the DRL on the performance of a p-i-n a-Si:H solar cell when moved from the p-i towards the i-n interface and as a function of its thickness. We investigate the effect of a buffer layer in between the p- and the i-layer on the external parameters of the solar cell. The presence of a buffer layer increases the electric field near the p-i interface, which leads to a higher collection of free charge carriers at the interface, although the electric field is then diminished deeper in the bulk. It appears that 10 nm thick buffer layer is sufficient to improve the performance. In case no buffer layer is applied, recombination losses at the p-i interface diminish the performance of the solar cell. We also observe that an increase of the DRL thickness results in a reduction of the solar-cell performance, which is more pronounced when the DRL is located in the region close to the p-i interface rather than close to the i-n interface.

The descriptive scattering parameters, haze and angular distribution functions of textured ZnO:Al transparent conductive oxides with different surface roughness are measured. An approach to determine the scattering parameters of all internal interfaces in p-i-n a-Si:H solar cells deposited on the glass/ZnO:Al substrates is presented. Using the determined scattering parameters as the input parameters of the optical model, a good agreement between the measured and simulated quantum efficiencies of the p-i-n a-Si:H solar cells with different interface roughness is achieved.

Computer simulations are reported of hydrogenated amorphous silicon germanium (a-SiGe:H) layers that make up the graded part of the intrinsic layer near the interfaces of a-SiGe:H solar cells. Therefore the graded part is approached with a ‘staircase’ bandgap profile, consisting of three layers within which the material properties are constant. Calibrated model parameters are obtained by matching simulation results of material properties of intrinsic a-SiGe:H single layers to measurements. Using the obtained model parameter sets subsequent simulations of p-i-n devices with intrinsic material similar to the single layers are matched to measured current-voltage characteristics. The changes in parameter values are evaluated as a function of optical gap.

We developed a novel temporary-superstrate concept for SnO2/p-i-n amorphous silicon solar cells. This concept combines roll-to-roll manufacturability, the utilization of light scattering, the conductive properties of SnO2:F, and the possibility of monolithic series connection. To this purpose, the deposition of high quality textured SnO2:F layers on aluminum foil has been developed using APCVD. Layers have been obtained with a transmission of 80 % and a sheet resistance of 12 Ω/□. After definition of the entire p-i-n cell structure including the back contact, the cell is laminated with a permanent carrier foil. By removing the aluminum foil, light can enter the cell through the textured TCO layer. A wide variety of transparent encapsulants can be used to finalize the (flexible or preshaped) product. Preliminary cells made according to this scheme have an efficiency of 6 %.