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Entwicklung und Charakterisierung von III-V-Weltraumsolarzellen

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BAUR, Carsten, 2007. Entwicklung und Charakterisierung von III-V-Weltraumsolarzellen [Dissertation]. Konstanz: University of Konstanz

@phdthesis{Baur2007Entwi-5066, title={Entwicklung und Charakterisierung von III-V-Weltraumsolarzellen}, year={2007}, author={Baur, Carsten}, address={Konstanz}, school={Universität Konstanz} }

2011-03-24T14:52:50Z 2011-03-24T14:52:50Z 2007 terms-of-use Baur, Carsten Entwicklung und Charakterisierung von III-V-Weltraumsolarzellen deu Baur, Carsten application/pdf With this work an important contribution in the field of characterisation of multi-junction solar cells and in the understanding of the degradation behaviour of III-V multi-junction cells for space applications has been made.<br />An extensive degradation study has been performed on the current state-of-the-art space solar cell of the European manufacturer RWE SSP (RWE3G28). Thereby, the applicability of available methods for the prediction of solar cell degradation in space due to particle irradiation has been investigated on multi-junction solar cells. It was demonstrated that a direct transfer of those methods, which were previously developed only for single-junction solar cells, to multi-junction solar cells is not possible in a strict sense. A correct extension both, from a mathematical and physical point of view, of the so called JPL (Jet Propulsion Laboratory) and especially of the NRL (Naval Research Laboratory) method for the prediction of the degradation behaviour of solar cells in space requires the knowledge of the degradation characteristics of all the subcells of the multi-junction stack under investigation. This was proven by the parallel investigation of the degradation behaviour of component cells.<br />The knowledge of the degradation behaviour of component cells and therefore the subcells in a multi-junction stack allows the extension of the existing models to arrive at a consistent description of the degradation behaviour of the more complex 3J or multi-junction solar cells.<br />By analysing dark I-V characteristics of component cells before and after irradiation a new method was developed which allows the derivation of the light I-V parameters and their degradation behaviours from applying the two-diode model which represents a mathematical description of the I-V characteristic of solar cells. This method is based on fundamental physics and is easy to apply to any kind of multi-junction solar cell.<br />Another main focus of this work was put on the conduction of a systematic uncertainty analysis for the calibration of multi-junction solar cells as it is performed at the calibration lab of the Fraunhofer ISE (ISE CalLab). Thereby, the complex interactions between the different subcells of a multi-junction solar cell were taken into account. This was done by first converting all influencing variables into uncertainties of the photocurrents of the different subcells. The impact of those uncertainties on the uncertainties of the relevant parameters of the multi-junction solar cells was then derived experimentally by carrying out spectrometric characterisations. Thereby, the changes of the solar cell parameters were monitored when changing the photocurrents of one of the subcells.<br />The results showed that the uncertainties of the solar cell parameters when measuring multi-junction solar cells are close to the ones typically obtained when measuring single-junction solar cells.<br />Apart from the main topics of this work uncertainty analysis and degradation study significant contributions were made for the development of the current state-of-the-art 3J solar cell from RWE SSP (RWE3G28). It was demonstrated that precise characterisations and correct interpretation of the measurement results are of great importance in defining the direction for the next development steps.<br />A new possibility for deriving or assessing the lifetimes of the minority carriers in solar cells was identified by analysing the signals obtained within spectral response measurements of Ge component cells due to optical coupling. However, to quantify the result a very detailed knowledge of the structure of the component cell is required. Moreover, the dependencies of the optical coupling or photon recycling on various influencing parameters (in dependence of the structure) have to be known.<br />Taking the insolation (spectral distribution and intensity) as an example for an influencing parameter, opposing dependencies of the signal in the spectral response measurement due to optical coupling were obtained for two different structures. First possibilities that explain these differences are described.<br />Finally, the main fields of interest of current research programs were described which have the potential of improving efficiency and/or the radiation stability of III-V multi-junction solar cells. As an important point hereby, the development of a 1 eV material based on the material combination (GaIn)(NAs) has been identified. Significant improvements of the material quality of (GaIn)(NAs) have been achieved by applying appropriate annealing steps after the growth. These improvements would allow already a profitable introduction of a (GaIn)(NAs) subcell into a 6J solar cell.<br />Nevertheless, the aim in the long-term is the development of a 4J solar cell for which the quality of the (GaIn)(NAs) subcell still has to be improved. Development and Characterisation of III-V Space Solar Cells

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