Research On Degradation Of GaAs Solar Cells In Space Radiation Environment

GaAs solar cells are the main energy source for various spacecraft in space.The improvement of process and structure makes photoelectric conversion efficiency improve continuously,so solar cells are more and more widely used in space.However,the performance of solar cells will suffer degradation as the space radiation which will threaten the safety of the spacecraft.Therefore,it is essential to study the mechanism of radiation damage for solar cells in space.In the study,the mechanism of performance degradation of muti-junction III-V Ga As solar cells was analyzed and the 1MeV electron and 10 Me V proton experiments were carried out.After that,two different model were established to analyze the experimental data.(1)An empirical model was established by using the flux analysis method.The results showed that under the condition of electron irradiation,the solar cell performance begins to decline when the flux is larger than 1013/cm~2,but for proton irradiation,the solar cell performance begins to decrease when the flux is larger than 10~10/cm~2.(2)Based on the defect analysis method,the correlation between material defects and radiation environment was studied.Firstly,molecular dynamic(MD)method was used to simulate the characteristics of defects caused by primary know-on atom(PKA).And the main results were as follows: collision cascade can be divided into three stages and "displacement spike" appeared at about less than 1ps;atom displacement threshold energy is about 12.5eV;the number of defects in stable state and “displacement spike” agree with simple Kincin-Pease theory;the radiation damage would be more serious with the increasing energy of PKA;the defects distributed in a sphere region with a radius of 100?.In addiation,the influence of PKA direction and temperature on the number of steady Frenkel pairs had also been researched,the number of Frenkel pairs is insensitive to PKA direction,but had a trend to elevate firstly and then decrease with the temperature increasing,the critical temperature is 750 K.The number of defects is lager when the PKA is Ga.For energy of PKA and temperature,the percentage of interstitial is higher than vacancy defect in clusters,while vacancies tend to form larger clusters.Then monte carlo(MC)simulation and molecular dynamic was carried out to simulate the defect density after irradiation.And a microscopic method was established based on the defects density parameter.It can conclude that the critical defect density which lead to the degradation of three-junction Ga As solar cells performance is ~ 1017 /cm3 after both electron and proton irradiation.According to this,degradation of solar cell performance can be predicted only by defect density,not a large number of experimental data or the type of radiation particles.In addition,the proton radiation has more serious effect on the performance of solar cell than electron radiation.But the degradation caused by proton radiation is more serious,it is due to different PKA spectra for proton and electron radiation,and the evolution of defect is different.