There are three ways in which the cell efficiency of silicon solar cells may be improved by better exploitation of the solar spectrum: down-conversion (cutting one high energy photon into two low ...energy photons), photoluminescence (shifting photons into wavelength regions better accepted by the solar cell) and up-conversion (combining low energy photons to one high energy photon). In this paper, we present the state of the art of these three methods and discuss the suitability of materials available today for application to silicon solar cells.
In a dc-driven planar gas discharge system with a semiconductor electrode, the homogeneous stationary discharge state can be destabilized in favor of current filaments. A filament consists of a ...succession of spatially confined breakthroughs of the gas layer that repeatedly take place at approximately the same position. A pulsating filament is thus slowly moving over the active area of the system. At fixed parameters, processes of creation and quenching of filaments are observed, while their average spatial density depends on control parameters. Depending on the density, filaments arrange in different configurations. At an intermediate value of filament density, a pattern on a two-dimensional domain is found: it is a spatially anisotropic chain pattern that is specified by two characteristic spatial scales. It is suggested that the observed phenomena are due to a Hopf-Turing instability arising in the system.
Two approaches can be followed to reduce thermalisation and transmission losses in solar cells and thereby better exploit the solar spectrum. Firstly, modification may be done to lower energies, ...which can be via down-conversion, where one high energy photon is split into two or more low energy photons, or photoluminescence, where photons are shifted into different wavelength regions. Secondly, modification may be done to higher energies using up-conversion, where two or more low energy photons are combined to form one high energy photon. In this paper, the state of the art of these methods and the suitability of materials available today for application to silicon solar cells are presented
A planar pattern forming semiconductor gas-discharge device is examined. While being driven with a stationary voltage, it generates patterns that contain domains oscillating with different ...frequencies. The multioscillatory pattern is formed in a sequence of bifurcations from the homogeneous stationary state. A nonlinear interaction between different parts of the pattern can be detected. It is suggested that the observed behavior is due to the coupling of processes in two nonlinear components, the gas-discharge gap and the semiconductor cathode fabricated from high resistance gallium arsenide.
A planar dc gas discharge system with a high Ohmic semiconductor cathode is investigated with respect to temporal destabilization of the stationary homogeneous state. A subcritical Hopf bifurcation ...is observed, leading to a spatial homogeneous oscillation. The dependence of the oscillator's properties on control parameters is investigated. By applying spatial nonuniform optical control of the semiconductor cathode, several domains that may oscillate on different frequencies can be created. These spatially homogeneous domains can interact with each other through common boundaries. By adjusting the strength of coupling of the domains, their interaction can be controlled. In this interaction, regularities have been found that are, in some aspects, similar to those observed in externally driven nonlinear oscillators.
One-dimensional modeling of a Peltier element Seifert, W.; Ueltzen, M.; Strumpel, C. ...
Proceedings ICT2001. 20 International Conference on Thermoelectrics (Cat. No.01TH8589),
2001
Conference Proceeding
For dimensioning and optimum control of Peltier coolers and heat pumps, an accurate numerical description of the performance parameters under various operation conditions is required. Here, the ...situation for homogeneous bismuth antimony telluride based Peltier cooler material is discussed, using representative values of constant material parameters in comparison to real experimental data of the temperature dependence of the thermoelectric properties. For the case of a constant pellet cross section, given pellet length and neglecting heat transfer aside, the problem can be treated as one-dimensional. The relation between electric current density j, temperature difference /spl utri/T, and absorbed cooling power or COP, respectively, along a single Peltier element have been considered by ab-initio calculations and plotted for the entire two-dimensional range (over j and /spl utri/T) of relevant operating conditions, assuming constant material properties. Accordingly, the spatial temperature distribution inside the thermoelectric material has been calculated. Differential equations governing thermoelectric transports have been analytically and numerically solved by the software tool MATHEMATICA. This instrument is capable of solving the inhomogeneous second order differential equation for the temperature profile even for nonconstant coefficients with mixed boundary conditions provided. Thus, exact temperature profiles along the pellet can be easily calculated taking into account the correct temperature dependence of the material properties. The maximum temperature difference has been determined for arbitrarily given cooling power or COP, respectively, including zero temperature difference and adiabatic cold side (/spl Delta/T/sub max/) cases. Evidence is provided for a very good quantitative agreement between /spl Delta/T/sub max/ values calculated using real temperature dependent material properties or volume averaged constant values.
Zigzag destabilization of self-organized solitary stripes was detected recently in the current density of a planar semiconductor gas discharge system. In the present work it is revealed that this ...instability is accompanied by the propagation of the zigzag deformation along the body of a stripe. This phenomenon is quantitatively analyzed using a high-speed image acquisition technique based on a framing camera system. The velocity of propagation has been found to increase monotonously with the global electric current, while the characteristic wavelength of the pattern shows a complicated behavior. The connection of the obtained data to available results of theoretical analysis of secondary bifurcations of solitary stripes in reaction-diffusion media is considered.
Migration from the previous generation of Advent Solar emitter wrap-through (EWT) cells to the current technology platform based on 243 cm 2 multicrystalline Si cells and monolithically ...interconnected cell and encapsulated modules has brought with it significant performance increases. Extraction of current from multiple contact pads distributed on the cell rear, optimization of the emitter through-holes, and reduction of through-hole lengths associated with moving to thinner silicon wafers has led to significantly reduced series resistance. Ag metallization costs are also lowered because of the reduction of grid finger lengths. Improved isolation between interdigitated p and n regions on the cell rear has lead to negligible shunt resistance losses. This, in combination with understanding of diode recombination losses, passivation, and optimization of Si material for the cell design through appropriate choice of base resistivity has lead to a greater than one percent absolute efficiency improvement over previous generation EWT cells, with best multicrystalline Si cells producing 17% conversion efficiency using the regular production processes. Additional improvements to efficiency are obtained with the implementation of texturing. These efficiency gains are further leveraged on the module level by the reduction of series resistance losses associated with the backplane interconnect design compared to conventionally interconnected front-side contacted cells.
