Performance Analysis of Lattice-Matched 5- and 6-Junction III-V Solar Cells
Määttä, Seela (2025)
2025
Teknis-luonnontieteellinen DI-ohjelma - Master's Programme in Science and Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2025-03-05
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202503042569
https://urn.fi/URN:NBN:fi:tuni-202503042569
Tiivistelmä
The increasing global demand for energy requires sustainable solutions. As a renewable energy source, solar energy provides a cleaner and greener alternative to traditional fossil fuel sources. Multijunction solar cells, composed of III-V semiconductors, have become the standard for power generation in space applications and in concentrator photovoltaic systems. The lattice-matched monolithic 5- and 6-junction solar cells investigated in this study consist of junctions, also known as subcells, made from different semiconductor materials. Each subcell is designed to absorb and convert light to electric power at specific wavelengths of the solar spectrum. Increasing the number of junctions can improve efficiency, but it also leads to an increased probability of various loss mechanisms.
The performance of 5- and 6-junction solar cells can be assessed using various characterization methods. In this work, the current-voltage characteristics and external quantum efficiency of multijunction solar cells were analyzed. The objective was also to examine the performance of individual junctions since each junction has a direct impact on the overall performance of the multijunction solar cell.
The measurement results indicated that the open-circuit voltage of the multijunction cell is nearly directly proportional to the number of junctions. Efficiency was also expected to increase with the number of junctions, but the measurement results did not exhibit a linear growth due to various loss mechanisms. Measurements with concentrated light indicated a linear increase in current with intensity for both 5- and 6-junction cells up to 600 suns. The influence of temperature on the open-circuit voltage was evident when comparing the modeled and measured values.
Precisely evaluating the electrical characteristics of individual subcells in multijunction solar cells is crucial for further development. In this study, these characteristics were examined through current matching and external quantum efficiency measurements. External quantum efficiency was assessed by measuring the short-circuit current at specific wavelengths under defined light bias conditions. The quantum efficiencies for a GaAs-based 5-junction solar cell were determined using this method, demonstrating agreement with simulated results.
The short-circuit current density values of the subcells generally matched well, except for the bottom cell, which exhibited a notably lower value. This discrepancy was also observed in current matching measurements for the GaAs-based 5-junction cell. This confirms the assumption that optimizing the bottom cell is the most challenging among the subcells and thus remains a primary focus in research. Additionally, minimizing voltage losses through material optimization could further enhance efficiency up to 50%. However, the initial demonstrations of 5- and 6-junction structures show promise for future development.
Characterizing individual subcells in series-connected multijunction solar cells poses challenges due to their interdependence. The use of various measurement methods together enables a reliable and comprehensive overview of the solar cell's operation. Isolating the electrical properties of individual junctions and identifying potential defects are fundamental steps in advancing next-generation multijunction solar cell technologies.
The performance of 5- and 6-junction solar cells can be assessed using various characterization methods. In this work, the current-voltage characteristics and external quantum efficiency of multijunction solar cells were analyzed. The objective was also to examine the performance of individual junctions since each junction has a direct impact on the overall performance of the multijunction solar cell.
The measurement results indicated that the open-circuit voltage of the multijunction cell is nearly directly proportional to the number of junctions. Efficiency was also expected to increase with the number of junctions, but the measurement results did not exhibit a linear growth due to various loss mechanisms. Measurements with concentrated light indicated a linear increase in current with intensity for both 5- and 6-junction cells up to 600 suns. The influence of temperature on the open-circuit voltage was evident when comparing the modeled and measured values.
Precisely evaluating the electrical characteristics of individual subcells in multijunction solar cells is crucial for further development. In this study, these characteristics were examined through current matching and external quantum efficiency measurements. External quantum efficiency was assessed by measuring the short-circuit current at specific wavelengths under defined light bias conditions. The quantum efficiencies for a GaAs-based 5-junction solar cell were determined using this method, demonstrating agreement with simulated results.
The short-circuit current density values of the subcells generally matched well, except for the bottom cell, which exhibited a notably lower value. This discrepancy was also observed in current matching measurements for the GaAs-based 5-junction cell. This confirms the assumption that optimizing the bottom cell is the most challenging among the subcells and thus remains a primary focus in research. Additionally, minimizing voltage losses through material optimization could further enhance efficiency up to 50%. However, the initial demonstrations of 5- and 6-junction structures show promise for future development.
Characterizing individual subcells in series-connected multijunction solar cells poses challenges due to their interdependence. The use of various measurement methods together enables a reliable and comprehensive overview of the solar cell's operation. Isolating the electrical properties of individual junctions and identifying potential defects are fundamental steps in advancing next-generation multijunction solar cell technologies.