基于分布式布拉格反射器结构的空间三结砷化镓太阳能电池抗辐照研究

Anti-radiation of space triple-junction solar cell based on distributed Bragg reflector structure

根据电子辐照条件下的常规三结砷化镓太阳能电池光谱响应以及电池电流的损伤特征,确定电池衰减的物理机理:中电池在电子辐照后形成的辐照损伤缺陷,使得基区少子扩散长度被大幅缩短,影响了光生载流子的收集.针对中电池衰减的物理机理,设计不同的基区厚度,验证辐照后扩散长度缩短至1.5μm左右.为提升中电池抗辐照性能,消除辐照后扩散长度缩减带来的影响,对中电池外延结构进行设计,将中电池基区减薄至1.5μm,并在其下方嵌入分布式布拉格反射器,对特定波段光反射进行二次吸收,弥补中电池减薄的影响.通过TFCalc光学模系设计软件模拟出的中心波长为850 nm,15对Al_(0.9)Ga_(0.1)As/Al_(0.1)Ga_(0.9)As的分布式布拉格反射器,实际测试最高反射率大于97%,高反带宽94 nm,能够满足设计要求.此基础上进行了新结构电池的外延生长与辐照测试对比.实验结果表明:新结构太阳能电池辐照后短路电流衰减比原结构降低了50%,效率的剩余因子提升2.3%.

At present,solar cells are the main sources for spacecrafts.For a long time the bulk of the space power installations has been the solar arrays based on single junction silicon and gallium arsenide solar cells.In recent years a trend has been the active use of triple-junction Ga As solar cell with higher efficiency instead of single junction solar cells.One of the most important characteristics of solar cells used in spacecrafts is the resistance to radiation damages caused by high energy particles of the near-Earth space.According to the spectral response of triple-junction Ga As solar cell and the damage characteristics of the current under the condition of electron irradiation,the physical mechanism of cell attenuation can be determined：the current degradation originates mainly from the Ga In As subcells.These damages form additional centers of nonradiative recombination,which results in the reduction of the minority charge carrier diffusion lengths and in degradation of the solar cells photocurrent.The radiation damage caused by the electron irradiation will shorten the diffusion length of the base region and affect the collection of photo generated carriers.The ways of improving absorption of long wavelength light in Ga In As subcells with a thin base in using the distributed Bragg reflector can be investigated by the mathematical simulation method based on calculating the light propagation in a multilayer structure by means of the TFCalc software which can design optical structure.To estimate the validity of these methods for solar cells structures with distributed Bragg reflector,the spectral dependences of the photoresponse and the reflection coefficient with different base thickness values are calculated and compared with experimental results.Based on the physical mechanism of the degradation,the thickness of middle subcell base layer is reduced,and an appropriate structure of the distributed Bragg reflector is simulated by the TFCalc software.As a result,the new structure solar cells are that the thickness of the base layer is 1.5 μm compared with the different middle subcell thickness values,and the distributed Bragg reflector structure with 15 paris of the Al0.1Ga0.9As/Al0.9Ga0.1As with 850 nm central wavelength is embedded in the middle subcell of the base layer,the distributed Bragg reflector has a highest reflectivity of more than 97% in the actual test,and a bandwidth of 94 nm,which can satisfy design requirement.After irradiating the new structure of solar cells,the decay of its short-circuited current is reduced by 50% compared with that of the original structure,and the remaining efficiency factor is increased by 2.3%.