Effects Of Electron Irradiation Degradation In High-Efficiency GaAs Multi-Junction Solar Cells And Optimization Design

Lattice-matched triple-junction solar cells have the advantages of high conversion efficiency,strong irradiation resistance,and good thermal stability,which have completely replaced silicon solar cells and become the most widely used space solar cells.However,for this kind of solar cell,the improvement of begin of life（BOL）and end of life（EOL）is the main problem that needs to be solved.In this work,by using finite element simulation software,combined with related optical performance optimi-zation and irradiation effect simulation software,the lattice-matched triple-junction solar cell was designed and optimized.Based on the optimization results,all samples were prepared by Metal-organic Chemical Vapor Deposition（MOCVD）system,and anti-reflection（AR）coatings were prepared by electron beam evaporation system.1Me V electron irradiation was performed on all samples,and four different fluence points were selected for comparison to explore the irradiation damage effects and mechanism of solar cells and AR coatings.By analyzing the in-orbit environment of spacecrafts,the irradiation resistant reinforcement approach of lattice-matched triple-junction solar cell was proposed,which provides a certain theoretical support and optimization direction.The results in this work show that the lattice-matched triple-junction solar cell model designed by APSYS finite element simulation software has a good agreement with the actual grown solar cells in terms of electrical performance.At the same time,the AR coatings designed by Essential Macleod Program and the actual deposited AR coatings also have a good consistency in optical performance.1 Me V electron irradiation was carried out on the solar cell,the light characteristics,dark characteristics and spectral response of the solar cells after irradiation showed that the degradation of the In Ga As middle cell was the most serious,and it became the current limiting junction of triple-junction solar cell after irradiation.Based on the above measured results,the APSYS was used to establish the multi-junction solar cell high-energy electron irradiation degradation model,and the changes of the energy band,electric field,and minority carrier lifetime after irradiation were analyzed and revealed the degradation mechanism of irradiation.Based on the degradation model of high-energy electrons in multi-junction solar cells,it is found that irradiation will cause damage to the hetero-interface of solar cells,which will further reduce the minority carrier lifetime and reduce the short-circuit current density of solar cells.The damage coefficients of minority carriers in the emitter and base regions of the Ga In P top cell and In Ga As middle cell were also calculated,which were 2.0×10^-6cm²/s、1.3×10^-6cm²/s、8.4×10^-7cm²/s and 1.6×10^-7cm²/s,respectively.It quantitatively shows that in the lattice-matched triple-junction solar cell,the degradation of the In Ga As middle cell is greater than that of the Ga In P top cell.The AR coatings were also subjected to 1 Me V electron irradiation.The refractive index,reflectance and extinction coefficient of all samples after irradiation showed that the damage caused by irradiation is not the same for different materials.For the Ti O₂and Al₂O₃ coating,the refractive index decreases with the increase of the irradiation fluence,however,for the Mg F₂ coating,the refractive index increases with the increase of the irradiation fluence.After irradiation,the average reflectivity of the triple-layer AR coating increases in the short wavelength region and decreases in the medium and long wavelength region,and the central wavelength of the coating was red-shifted.Finally,the geosynchronous orbit（GEO）and the low-earth orbit（LEO）environment were introduced,and the irradiation environment of the spacecraft in different orbit was summarized.Combining the degradation results of solar cells and AR coatings after 1 Me V electron irradiation,two irradiation resistance approaches were proposed:For solar cells in LEO,increasing the BOL can effectively increase the output power of the solar cell array,therefore,the AR coating design and optimization of the solar cells can be used to increase the BOL of the solar cells;For solar cells in GEO,the EOL of solar cells can be increased by optimizing the thickness of the active layer of the In Ga As middle cell.According to the calculation results by APSYS,the EOL of the solar cells has increased from 26.38%to 27.91%.