Design, Fabrication And Reliability Study Of Concentrator Multi-junction Solar Cells

Since the global energy crisis and environmental pollution are increasingly serious, it is vital for the sustainable development of human society to explore renewable energy. Recently, photovoltaic technology has attracted increasing attention, which can convert sunlight into electricity. Concentrator photovoltaic with its special advantages, such as higher efficiency and lower cost, has been recognized to be the most promising power generation technology for terrestrial application. Concentrator multijunction solar cell is the key of concentrator photovoltaic, and has the highest photoelectric conversion efficiency, good temperature characteristic, superior radiation-resistant property, and long lasting lifetime span, and so on. This work is mainly divided into three parts, cell design, device fabrication and reliability study for the III-V compound semiconductor concentrator multi-junction solar cells, and the main achievements are summarized as follows:1. The theoretical study on concentrator GaInP/GaAs/Ge triple-junction solar cell was carried out. Firstly, by changing the doping concentration of p-and n-layer, interface recombination and carrier mobility, and so on, the characteristics of three subcells from concentrator GaInP/GaAs/Ge triple-junction solar cell, GalnP top cell, GaAs middle cell and Ge bottom cell, were investigated. Secondly, in order to achieve high efficiency under high concentration, the subcell structures, especially emitter structure of GaInP top cell, were designed and optimized. Finally, by complying with current matching of subcells, high-efficient concentrator Ga0.5In0.5P/GaAs/Ge triple-junction solar cell was obtained with efficiency of 38.1%at 1000 suns.2. The key techniques of growing concentrator GaInP/InGaAs/Ge triple-junction solar cell were studied. By exploring the MOCVD growth process, we solve the problems for expitial growth, such as anti-phase domains, lattice-matching, and ordering in GalnP semiconductor, and achieve the epitaxial growth of high-quality and high-efficient single-junction subcells, Ga0.51In0.49P top subcell, In0.01Ga0.99As middle subcell and Ge bottom subcell. By optimizing the growth condition for high-doping and ultrathin epitaxial layer, high-performance GaAs tunneling junction with peak tunneling current density of 150A/cm2 was obtained. And epitaxial growth of high quality triple-junction solar cell with lower surface defect was achieved. Then, investigating into the influence of the ratio of electrode width and space on characteristics of multijunction solar cells, the optimal electrode pattern was obtained. By designing and optimizing antireflection film structure, the optimal Al2O3/TiO2 dual-layer film shown superior performance, enhancing short-circuit current of solar cell by 33.3%. Finally, the high-performance GaInP/InGaAs/Ge triple-junction solar cell was obtained with efficiency of 39.2%at 1000 suns.3. Reliability of concentrator multi-junction solar cell was studied. First, by 3-D equivalent circuit model, the characteristics of surface defect of multi-junction solar cells were studied under illumination and external constant current source, respectively, and it was found that the power degradation of multijunction solar cell with surface defect is greater under external constant current source than that under illumination. Then, according to IEC 62108 standard the accelerated aging tests of cell samples with good surface and defective surface were carried out, and the aging results showed that the performance degradation of all samples was within 8%, meeting the requirement of IEC 62108 standard.4. The theoretical study on the novel III-V compound semiconductor solar cells was carried out. Firstly, the characteristics of strain-compensated multi-quantum well GaAs solar cells with different molar fraction In1-xGaxAs/GaAsyP1-y multi-quantum wells were simulated, and in contrast with GaAs control sample, strain-compensated multi-quantum well GaAs solar cells showed higher short-circuit current, but lower open-circuit voltage, fill factor, and efficiency. In addition, the novel strain-compensated multi-quantum well AlGaAs/GaAs solar cell was studied, and shown higher short-circuit current and open-circuit voltage, but the lowest fill factor. Secondly, considering the special structure of metamorphic GaInP/InGaAs/Ge triple-junction solar cell, the influence of dislocation density on performance parameters of solar cell was studied, and it was found that solar cell efficiency shows visual degradation with more than 106/cm2 of dislocation density. In addition, investigating into efficiency dependence of metamorphic GaInP/InGaAs/Ge triple-junction solar cell on sun concentration, the highest efficiency was obtained at 300 suns. Finally, the theoretical study on the novel InGaN solar cell was carried out, and the higher efficiency of 20.8%was obtained by using n-on-p device structure. By investigating into the influence of dislocation density on the characteristics, the greater stability and durability of InGaN solar cell was shown compared with GaAs solar cell.