Optimization Design And Performance Research Of High-Efficiency Semiconductor Solar Cells

Currently,the major faced difficulty in photovoltaic power is still how to effectively reduce the power generation cost.Improving the photoelectric conversion efficiency of solar cells and reducing the usage of semiconductor materials,which are effective ways to reduce the cost of photovoltaic power generation.The research of new battery materials and battery structures has always been a hot topic in the field of photovoltaics.Among all types of solar cells,mono-crystalline silicon solar cells,with relatively high conversion efficiency,low cost and attenuation,are the earliest photoelectric conversion device putting into real application,and have been occupying the high market share of ground photovoltaic cells.Besides,GaAs-based ?-? triple-junction solar cells always have taken the leading position in photoelectric conversion efficiency due to their large optical absorption coefficient and excellent spectral response characteristics.In this paper,we mainly focus on the structure optimization and performance research of those two types of solar cells under different working conditions.The specific research results are as follows:1.We have explored a series of computational code in the framework of Matlab to simulate the performance of single-junction and multi-junction solar cells.In the design of the algorithm framework,both realistic structural-dependent quantum efficiency and the recombination current in the depletion region have been considered.By tuning various device parameters according to different semiconductor materials,the code can be widely applied to single-junction,multi-junction compound semiconductor solar cell device model.2.Since the radial p-n junction is perpendicular to the incident light and has periodicity and symmetry on the structure,we extend the traditional planar solar cell device model to the cylindrical coordinate system,and build the physical model suitable for the radial p-n junction solar cell structure optimization.Furthermore,a structural unit of radial p-n junction mono-crystalline silicon solar cells is optimized based on this model.Our calculation demonstrates the optimum theoretical efficiency of 33.11%can be achieved as that the radius of n+-Si core is 1?m,the radius of cylinder is 40 ?m,and the height of cylinder is 100 ?m,which is 5%higher than the theoretical conversion efficiency of conventional planar mono-crystalline silicon solar cells.Finally,based on the above optimization results,a preparation scheme of radial p-n junction mono-crystalline silicon solar cells is proposed.3.According to the spectral response of triple-junction GaAs solar cells and the damage characteristics of the current under the condition of electron irradiation,the current mismatch between the subcells can be determined,which results in degradation of the solar cell perform.In this paper,we can improve the radiation resistance of the Ga0.51In0.49P/In0.01Gao.99As/Ge triple-junction solar cells by optimizing the thickness of the triple-junction solar cells under different electron irradiation conditions and a thin base in using the distributed Bragg reflector(DBR).Based on the physical model of multi-junction solar cell devices,combined with the radiation damage mechanism of solar cells for space,the subcell thicknesses in triple-junction GaAs solar cells with and without DBR are simulated and optimized for different electron irradiation fluence to achieve current matching among the subcells.Our optimization results show:under irradiation with 1 MeV electrons at a dose of 1×1015 and 3×105 cm-2,the theoretical efficiency of the triple-junction solar cells without DBR is 35.47%and 33.82%,in comparison to optimization before,increased by 1.6%and 2.7%,respectively.The new triple-junction solar cells with DBR raised 1.8%and 3.2%,respectively.4.For the Ga0.51In.49P/In0.01Ga0.99As/Ge triple-junction solar cells,it is difficult to further improve the efficiency due to the limited bandgap combination.Therefore,an inverted metamorphic(IMM)triple-junction solar cell is designed by replacing the Ge subcell with the adjusted bandgap InxGa1-xAs subcell.Our optimization shows the nominal theoretical efficiency 45.91%can be achieved as that the bandgap of InxGa1-xAs bottom subcell is 1.0 eV,the subcell thickness combination is 2.04,4.40,and 3.79 ?m.Base on the optimized results above,we have fabricated the IMM GaInP/GaAs/In0.31Ga0.69As triple-junction solar cells using InxAl1-xAs step-graded buffer layer.The efficiency of the designed cell with an area of 30.25 mm2 is 33.02%under 1-sun,AM1.5D(1000 W/m2)spectrum,25 ? conditions.5.Following the similar routine,we have also designed the inverted triple-junction tandem device with two metamorphic junctions,namely GalnP/In0.02Ga0.98As/In0.33Ga0.67As,of nominal theoretical efficiency 46.68%with the optimal subcell thickness combination of 7.92,6.41,and 10.97 ?m.Based on the model of minority lifetime introduced dislocations,we have further studied this misfit-induced dislocation on the performance of inverted triple-junction tandem solar cells with one and two metamorphic junctions.Our simulation shows that the GaInP/In0.02Ga0.98As/In0.33Ga0.67As inverted triple-junction solar cell achieve from 0.20%to 0.37%efficiency improvement in comparison to the GaInP/GaAs/In0.31Ga0.69 solar cell,when the bottom subcell dislocation density is controlled between 3.68×105 cm2 and 8.70×106 cm-2,providing the useful guideline for the relevant device fabrication.