Numerical Analysis And Structural Optimization Of InGaN Solar Cells

Since the revised bandgap of InN at around 0.7eV, the bandgap of InGaN can be a perfect match with the solar spectrum, the bandgap of InGaN alloys can be varied by changing the compositions of indium, and InGaN has high absorption, high mechanical strength and some other special nature. These makes the study of InGaN become frontier research subject. However, the study of InGaN solar cells is still insufficient. The purpose of this dissertation is to provide a theoretical basis for preparation of InGaN solar cells. The main study contents include the following respects. First, we have simulate single-junction InGaN solar cells and InGaN solar cells inserting graded bandgap layers using the analysis of microelectronic and photonic structures (AMPS). And then, we have used MALTAB software to calculate the maximum efficiency of multi-junction solar cells and research the combination impact on solar cells. Main conclusions and work of this paper are drawn as follows:1,We use AMPS software to simulate InGaN solar cells. When the bandgap is 1.32eV and the doping concentration is 1×10¹⁸cm^-3, the maximum efficiency is 22.63%. When the thickness of p-layer and n-layer are both 200nm, the optimum bandgap is 1.4eV. We simulate a p-GaN/n-InxGa1-xN heterojunction solar cells, when the In content is 0.5, the maximum efficiency is 13.89%. p-GaN/n-In_0.5Ga_0.5N heterojunction has a valence band discontinuity.2,We respective insert many types graded bandgap layers into p-InGaN layer and n-InGaN layer of the homojunction solar cell which the bandgap is 2.3eV, p-GaN/n-In_0.5Ga_0.5N heterojunction solar cells and p-In_0.39Ga_0.61N/n-GaN heterojunction solar cells. Inserting graded bandgap layers not only improve the absorption efficiency of InGaN solar cells, but also constitutes barries and form additional electric field to improve the minority carrier collection and lifetime, reduce the valence band and conduction band discontinuty of the heterojunction solar cells, thereby enchance the conversion efficiency of the solar cells. We respective insert p-type and n-type graded bandgap layers into p-InGaN layer and n-InGaN layer of the homojunction solar cell. The efficiency of solar cells is improved from 11.50% to 14.30%. The efficiency of p-In_0.39Ga_0.61N/n-GaN heterojunction solar cells is only 0.005%. We insert n-type InGaN graded bandgap layers between p-InGaN/n-GaN heterojunction to remove the valence band discontinuity and improve the efficiency to 15.54%.3,We derive the formula of short-circuit current density of double-junction solar cells under recombination processes, then simulate the double-junction solar cells of different bandgap combination under AM1.5 global spectrum. The maximum efficiency is 31.93% when the bandgap combination is 1.74/1.1eV.4,The optimum efficiency of six junction is 38.56%. The efficiency increase with the increased number of sub-cells. The efficiency and J_sc are higher when there is no recombination.