Temperature coefficients of multicrystalline compensated silicon solar cells

Doktorgradsavhandling ved Fakultet for teknologi og realfag, Universitetet i Agder, 2016This thesis focuses on the bulk properties influencing the temperature coefficients of solar cells. The conversion efficiency of PV devices degrades with increasing temperature. The temperature coefficient of the open-circuit voltage can be improved by increasing the open-circuit voltage. Therefore with the continuous improvement of the conversion efficiencies over the last decades due to the global R and D efforts, the temperature sensitivity was continuously reduced. The major research question of this thesis is: are there other ways to improve the temperature sensitivity? It had been shown prior to the present work, that solar cells made of silicon processed by upgraded metallurgical routes had beneficial temperature coefficients compared to cells made of polysilicon. This effect was studied in this work, and it is shown that no significant difference is observed between cells with distinct compensation levels. This was made on a relatively small compensation level range. Another influencing parameter on the temperature coefficients is the height at which the wafer was picked in the ingot to be processed into a solar cell. The best temperature coefficients are most likely to be found at the top of the ingot. Yet the cell structure can change this result because of a larger variations of the cell parameters along the ingot height. It is known that reducing the bulk resistivity can improve the temperature coefficients. In the present work, the role of reducing bulk resistivity is examined with a focus on the impact on each cell parameter. It is shown that using a cell structure with a lower series resistance for a given bulk resistivity, is beneficial for the temperature coefficient of the fill factor. Light-induced degradation has a negative effect on the cell parameters, especially the open-circuit voltage. This degrades the temperature coefficients. Additionally the dependence of the temperature coefficients with irradiance was investigated. It is shown that the temperature sensitivity is intensified at low irradiance due to the decrease of the open-circuit voltage. In conclusion, it is shown that temperature sensitivity of solar cells can be controlled by adjusting various bulk parameters. The solidification step has a big impact on the temperature coefficients due to the cell parameters variations and the changes in recombination mechanisms. Moreover light-induced degradation deteriorates the temperature sensitivity

Temperature coefficients of compensated silicon solar cells - influence of ingot position and blend-in-ratio

Published version of an article in the journal: Energy Procedia. Also available on Science Direct: http://dx.doi.org/10.1016/j.egypro.2015.07.004Solar-grade silicon made from a metallurgical route presents boron and phosphorus compensation. Earlier work has shown that cells made from such material produce more energy than reference polysilicon modules when the temperature and irradiance is high. In the present study, solar cells from two different ingots with different blend-in-ratios were made from wafers at varying ingot heights in order to investigate how the temperature coefficients vary with compensation level and ingot height. The results suggest that solar modules made with solar cells from different ingot heights will perform differently at high temperature. It was also observed that the compensation level seems to have a smaller impact on the temperature coefficients than the ingot height

Experimental Investigation of the Optimal Ingot Resistivity for both the Cell Performances and the Temperature Coefficients for Different Cell Architectures.

acceptedVersionNivå

On the Variability of the Temperature Coefficients of mc-Si Solar Cells with Irradiance

The temperature sensitivity of silicon solar cells is in general assumed to be constant with irradiance in PV forecasting models, although it has been demonstrated experimentally that this is not true. In this study a theoretical model is established that describes the variation of the temperature coefficients of a silicon solar cell as a function of the irradiance. It is shown that the temperature sensitivity of the solar cell efficiency is decreasing with the irradiance and that the main reason for this behavior comes from the increase of the open-circuit voltage with light intensity. Moreover, a dependency of the cell's ideality factor on the irradiance has to be assumed to receive good modelling results that can be confirmed experimentally

Temperature coefficients of multicrystalline compensated silicon solar cells

This thesis focuses on the bulk properties influencing the temperature coefficients of solar cells. The conversion efficiency of PV devices degrades with increasing temperature. The temperature coefficient of the open-circuit voltage can be improved by increasing the open-circuit voltage. Therefore with the continuous improvement of the conversion efficiencies over the last decades due to the global R and D efforts, the temperature sensitivity was continuously reduced. The major research question of this thesis is: are there other ways to improve the temperature sensitivity? It had been shown prior to the present work, that solar cells made of silicon processed by upgraded metallurgical routes had beneficial temperature coefficients compared to cells made of polysilicon. This effect was studied in this work, and it is shown that no significant difference is observed between cells with distinct compensation levels. This was made on a relatively small compensation level range. Another influencing parameter on the temperature coefficients is the height at which the wafer was picked in the ingot to be processed into a solar cell. The best temperature coefficients are most likely to be found at the top of the ingot. Yet the cell structure can change this result because of a larger variations of the cell parameters along the ingot height. It is known that reducing the bulk resistivity can improve the temperature coefficients. In the present work, the role of reducing bulk resistivity is examined with a focus on the impact on each cell parameter. It is shown that using a cell structure with a lower series resistance for a given bulk resistivity, is beneficial for the temperature coefficient of the fill factor. Light-induced degradation has a negative effect on the cell parameters, especially the open-circuit voltage. This degrades the temperature coefficients. Additionally the dependence of the temperature coefficients with irradiance was investigated. It is shown that the temperature sensitivity is intensified at low irradiance due to the decrease of the open-circuit voltage. In conclusion, it is shown that temperature sensitivity of solar cells can be controlled by adjusting various bulk parameters. The solidification step has a big impact on the temperature coefficients due to the cell parameters variations and the changes in recombination mechanisms. Moreover light-induced degradation deteriorates the temperature sensitivity

Temperature coefficients of multicrystalline compensated silicon solar cells

Doktorgradsavhandling ved Fakultet for teknologi og realfag, Universitetet i Agder, 2016This thesis focuses on the bulk properties influencing the temperature coefficients of solar cells. The conversion efficiency of PV devices degrades with increasing temperature. The temperature coefficient of the open-circuit voltage can be improved by increasing the open-circuit voltage. Therefore with the continuous improvement of the conversion efficiencies over the last decades due to the global R and D efforts, the temperature sensitivity was continuously reduced. The major research question of this thesis is: are there other ways to improve the temperature sensitivity? It had been shown prior to the present work, that solar cells made of silicon processed by upgraded metallurgical routes had beneficial temperature coefficients compared to cells made of polysilicon. This effect was studied in this work, and it is shown that no significant difference is observed between cells with distinct compensation levels. This was made on a relatively small compensation level range. Another influencing parameter on the temperature coefficients is the height at which the wafer was picked in the ingot to be processed into a solar cell. The best temperature coefficients are most likely to be found at the top of the ingot. Yet the cell structure can change this result because of a larger variations of the cell parameters along the ingot height. It is known that reducing the bulk resistivity can improve the temperature coefficients. In the present work, the role of reducing bulk resistivity is examined with a focus on the impact on each cell parameter. It is shown that using a cell structure with a lower series resistance for a given bulk resistivity, is beneficial for the temperature coefficient of the fill factor. Light-induced degradation has a negative effect on the cell parameters, especially the open-circuit voltage. This degrades the temperature coefficients. Additionally the dependence of the temperature coefficients with irradiance was investigated. It is shown that the temperature sensitivity is intensified at low irradiance due to the decrease of the open-circuit voltage. In conclusion, it is shown that temperature sensitivity of solar cells can be controlled by adjusting various bulk parameters. The solidification step has a big impact on the temperature coefficients due to the cell parameters variations and the changes in recombination mechanisms. Moreover light-induced degradation deteriorates the temperature sensitivity

Experimental Investigation of the Optimal Ingot Resistivity for both the Cell Performances and the Temperature Coefficients for Different Cell Architectures.

acceptedVersionNivå

Simulated and measured temperature coefficients in compensated silicon wafers and solar cells

acceptedVersio

Temperature coefficients in compensated silicon solar cells investigated by temperature dependent lifetime measurements and numerical device simulation

publishedVersio