物理学报2016，Vol.65Issue(13)：138801-1-138801-7,7.DOI:10.7498/aps.65.138801
硅锗量子阱结构在硅异质结太阳电池中应用的数值模拟∗
Numerical simulation of silicon hetero junction solar cells with Si/Si1-xGex quantum wells
摘要
Abstract
Heterojunction with intrinsic thin-layer (HIT) solar cells attract attention due to their high open circuit voltage and stable performance. However, short circuit current density is difficult to improve due to light losses of transparent conductive oxide and hydrogenated amorphous silicon passivation (a-Si:H) layer and low absorption coefficient of crys-talline silicon (c-Si). Silicon germanium alloy (Si/Si1−xGex) quantum wells and quantum dots are capable of improving low light utilization by strong optical absorption in the infrared region. In this article, opto-electrical performances of the HIT solar cells integrated with Si/Si1−xGex quantum wells (HIT-QW) as a surface absorber are investigated by numerical simulation with Technology Computer Aided Design (TCAD). The influences of germanium content on the electrical performances of HIT solar cells with long carrier lifetimes of Si1−xGex layers (τ∗p ) and defect-free a-Si:H/c-Si interface are investigated at first. The simulation results indicate that optical utilization in the infrared region is enhanced with the increase of germanium fraction, while open circuit voltage degrades due to the decreasing of the en-ergy band gap of Si1−xGex, radiative recombination and auger recombination mechanism in the Si/Si1−xGex quantum wells. And the conversion efficiency reaches a maximum value at a germanium fraction of 0.25 then drops distinctly. When the germanium fraction increases from 0 to 0.25, the short circuit current density increases from 34.3 mA/cm2 to 34.8 mA/cm2, while the open circuit voltage declines from 749 mV to 733 mV. Hence, the conversion efficiency in-creases from 21.5% to 21.7% due to the fact that the enhancement of short circuit current density compensates for the reduction of open circuit voltage. When the germanium content increases to more than 50%, a serious open circuit voltage loss of more than 130 mV associated with the energy band gap loss of Si1−xGex arises in the HIT-QW solar cells, which indicates that the dominating carrier transport mechanism changes from shockley diffusion to recombination in the Si/Si1−xGex quantum wells. Subsequently, the influences of interface defects at a-Si:H/c-Si interface and bulk recombination centers in the Si/Si1−xGex quantum wells are discussed. Both interface holes at a-Si:H/c-Si interface and bulk holes in Si1−xGex quantum wells can be recombined through the interface defects at a-Si:H/c-Si interface and bulk recombination centers in the Si/Si1−xGex quantum wells, respectively, which restricts the position of hole fermi level in the open circuit condition. When the germanium fraction increases, the influence of interface defects at a-Si:H/c-Si interface becomes weak on the degradation of open circuit voltage compared with the significant influence of the bulk trap centers. Moreover,τ∗p of longer than 5 × 10−5 s is necessary for the retention of electrical performance of HIT-QW solar cells by the simulation. Based on this research, high-efficiency HIT solar cells can be achieved by incorporating high-quality Si/Si0.75Ge0.25 quantum wells, which also requires the impactful passivation of a-Si:H/c-Si interface.关键词
Si/Si1-xGex量子阱/异质结太阳电池/界面复合/a-Si:H/c-SiKey words
Si/Si1-xGex quantum wells/heterojunction with intrinsic thin-layer solar cell/interface recombination/a-Si:H/c-Si引用本文复制引用
张晓宇,张丽平,马忠权,刘正新..硅锗量子阱结构在硅异质结太阳电池中应用的数值模拟∗[J].物理学报,2016,65(13):138801-1-138801-7,7.基金项目
国家自然科学基金(批准号:61204005)资助的课题.* Project supported by the the National Natural Science Foundation of China (Grant No.61204005) （批准号:61204005）
