Presentation Information
[O12-P89]Development of wavelength-conversion materials for solar cells in space and stratospheric enviroments
*Haruto Hisazumi1 (1. Tomiokanishi High School)
Keywords:
Solar cell,Wavelength-conversion materials,Space,Stratosphere
1. Background and Purpose
The demand for solar cells for satellites is currently growing; however, existing cells cannot sufficiently utilize deep ultraviolet (UV) light present in space and stratospheric environments for power generation. This study aims to synthesise fluorescent materials that convert deep UV light into visible light, thereby improving the power generation efficiency of solar cells for satellites.
2. Methods of Experiment 1
Fluorescent materials Y2O3:Eu3+ and VYO4:Eu3+ were synthesised, applied to silicon solar cell surfaces, and their excitation and fluorescence spectra were measured (Fig. 1). Four types of cells were prepared-including untreated normal solar cells and Y2O3-coated non-fluorescent solar cells-and launched into the stratosphere together with a current measurement device (Fig. 2) to measure changes in current values from the ground to an altitude of approximately 27,000 meters(m).
3. Results and Discussion of Experiment 1
The current values of fluorescent material-coated solar cells at each altitude band were compared as relative values (Fig. 3). Fluorescent material-coated cells remained at approximately 30% of the normal solar cell value near the ground, and approximately 40% in the stratosphere. The primary cause is considered to be excessive visible light blocking due to the overabundance of fluorescent material. Insufficient luminescence efficiency due to non-optimized composition and uneven coating are also considered contributing factors. On the other hand, increases in current values were observed in VYO4:Eu3+-coated cells at altitudes of 10,000-15,000 m, and in Y2O3:Eu3+-coated cells at altitudes above 20,000 m. This is thought to result from differences in the excitation spectra of the two materials, leading to efficient absorption at different altitudes as UV levels increase. Furthermore, the reversal of the relative current values depending on altitude indicates that the optimal selection of fluorescent material depends on the operating altitude.
4. Methods of Experiment 2
Based on the results of Experiment 1, priority was given to improving visible light transmittance, and a method of placing fluorescent glass on the solar cell was adopted. Eu3+-doped fluoroborosilicate glass (50MgF2-33.3BaO-16.7B2O3-1Eu2O3), which excels in visible light transmittance and luminescence efficiency, was selected, synthesised, and characterized (Fig. 4). The fluorescent glass was then placed on the solar cell surface, and the current values under UV irradiation were measured (Fig. 5). The expected increase in current in a space environment was also estimated by theoretical calculation (Fig. 6).
5. Results and Discussion of Experiment 2
The visible light transmittance of the fabricated fluorescent glass was approximately 70%, an improvement over Experiment 1 (Fig. 4). However, prior research has achieved higher transmittance, and further improvement is expected through optimization of the synthesis process.The current value of the fluorescent glass-mounted solar cell under UV irradiation increased approximately 1.4-fold compared to the unmounted cell (Fig. 5), demonstrating that fluorescent glass can improve the current output. On the other hand, the current value in a space environment is expected to be approximately 26% lower than that of currently mainstream satellite solar cells (Fig. 6). The primary cause is insufficient visible light transmittance, and further improvement of both transmittance and luminescence efficiency remains a challenge.
6. Conclusion
High visible light transmittance of the fluorescent material is essential for improving the current output of solar cells. Glass forms are more advantageous than powdered forms in terms of ensuring transmittance. Furthermore, the optimal selection of fluorescent material depends on the operating altitude, requiring selection that accounts for the UV environment at each altitude.
7. Acknowledgments
The authors wish to express their sincere gratitude to Professor Osamu Sahara and Professor Toshihiro Moriga of Tokushima University, Professor Tomoya Konishi of Anan National College of Technology, GOCCO Co., Ltd., and Mr. Yoshiyuki Murakami of JAXA for their cooperation in this research.
8. References
(1) "Emission and Excitation Spectra of Europium-Activated Rare Earth Phosphors," Hitachi Review, May 1967, Ryuji Ozawa, Hisako Minegishi.
(2) "Effect of Mg2+ and fluorine on the network and highly efficient photoluminescence of Eu3+ ion in MgF2-BaO-B2O3 glasses," Shinozaki K, Sukenaga S, Shibata H, Akai T. The American Ceramic Society. 2019;102:2531-2541.
The demand for solar cells for satellites is currently growing; however, existing cells cannot sufficiently utilize deep ultraviolet (UV) light present in space and stratospheric environments for power generation. This study aims to synthesise fluorescent materials that convert deep UV light into visible light, thereby improving the power generation efficiency of solar cells for satellites.
2. Methods of Experiment 1
Fluorescent materials Y2O3:Eu3+ and VYO4:Eu3+ were synthesised, applied to silicon solar cell surfaces, and their excitation and fluorescence spectra were measured (Fig. 1). Four types of cells were prepared-including untreated normal solar cells and Y2O3-coated non-fluorescent solar cells-and launched into the stratosphere together with a current measurement device (Fig. 2) to measure changes in current values from the ground to an altitude of approximately 27,000 meters(m).
3. Results and Discussion of Experiment 1
The current values of fluorescent material-coated solar cells at each altitude band were compared as relative values (Fig. 3). Fluorescent material-coated cells remained at approximately 30% of the normal solar cell value near the ground, and approximately 40% in the stratosphere. The primary cause is considered to be excessive visible light blocking due to the overabundance of fluorescent material. Insufficient luminescence efficiency due to non-optimized composition and uneven coating are also considered contributing factors. On the other hand, increases in current values were observed in VYO4:Eu3+-coated cells at altitudes of 10,000-15,000 m, and in Y2O3:Eu3+-coated cells at altitudes above 20,000 m. This is thought to result from differences in the excitation spectra of the two materials, leading to efficient absorption at different altitudes as UV levels increase. Furthermore, the reversal of the relative current values depending on altitude indicates that the optimal selection of fluorescent material depends on the operating altitude.
4. Methods of Experiment 2
Based on the results of Experiment 1, priority was given to improving visible light transmittance, and a method of placing fluorescent glass on the solar cell was adopted. Eu3+-doped fluoroborosilicate glass (50MgF2-33.3BaO-16.7B2O3-1Eu2O3), which excels in visible light transmittance and luminescence efficiency, was selected, synthesised, and characterized (Fig. 4). The fluorescent glass was then placed on the solar cell surface, and the current values under UV irradiation were measured (Fig. 5). The expected increase in current in a space environment was also estimated by theoretical calculation (Fig. 6).
5. Results and Discussion of Experiment 2
The visible light transmittance of the fabricated fluorescent glass was approximately 70%, an improvement over Experiment 1 (Fig. 4). However, prior research has achieved higher transmittance, and further improvement is expected through optimization of the synthesis process.The current value of the fluorescent glass-mounted solar cell under UV irradiation increased approximately 1.4-fold compared to the unmounted cell (Fig. 5), demonstrating that fluorescent glass can improve the current output. On the other hand, the current value in a space environment is expected to be approximately 26% lower than that of currently mainstream satellite solar cells (Fig. 6). The primary cause is insufficient visible light transmittance, and further improvement of both transmittance and luminescence efficiency remains a challenge.
6. Conclusion
High visible light transmittance of the fluorescent material is essential for improving the current output of solar cells. Glass forms are more advantageous than powdered forms in terms of ensuring transmittance. Furthermore, the optimal selection of fluorescent material depends on the operating altitude, requiring selection that accounts for the UV environment at each altitude.
7. Acknowledgments
The authors wish to express their sincere gratitude to Professor Osamu Sahara and Professor Toshihiro Moriga of Tokushima University, Professor Tomoya Konishi of Anan National College of Technology, GOCCO Co., Ltd., and Mr. Yoshiyuki Murakami of JAXA for their cooperation in this research.
8. References
(1) "Emission and Excitation Spectra of Europium-Activated Rare Earth Phosphors," Hitachi Review, May 1967, Ryuji Ozawa, Hisako Minegishi.
(2) "Effect of Mg2+ and fluorine on the network and highly efficient photoluminescence of Eu3+ ion in MgF2-BaO-B2O3 glasses," Shinozaki K, Sukenaga S, Shibata H, Akai T. The American Ceramic Society. 2019;102:2531-2541.