Theoretical Simulation Of Trapping Structure Of Silicon-based Thin Film Solar Cells

With the serious aggravation of energy shortage and environmental pollution,more and more people begin to devote themselves to the development of solar cells.Crystalline silicon cell is the most important part of the photovoltaic market,the cost of conventional crystalline silicon cell is high due to the thick absorption layer.In order to reduce the production cost and save resources,people begin to design and develop ultra-thin crystalline silicon cell,nano-structure crystalline silicon cell and perovskite/crystalline silicon laminated solar cell.Therefore,how to reduce the optical absorption loss of each layer of the cell,improve the light absorption and achieve high intensity photocurrent density and high photoelectric conversion efficiency is an urgent problem to be solved.In view of the above problems,this paper studies in the following aspects:First,we designed and simulated the ultrathin crystalline silicon cells with single-sided pyramid texture and double-sided pyramid texture,revealing the dependence of trap structure on incident Angle.By adjusting the shape of pyramids,the maximum photocurrent densities reach 36.23 and 37.71 mA/cm² for the cells with front pyramids and double-sided pyramids,respectively.The reflectivity spectrum indicates that the double-sided pyramidal architecture remarkably suppresses light escape and then enhances the light absorption in long wavelength range,which makes the absorption of this kind of cell approach the Yablonovitch limit.The calculated conversion efficiencies of the planar reference cell,the cells with front and double-sided pyramids are 16.94%,19.65%and 20.45%respectively.Additionally,the difference between randomly and periodically textured cells was investigated and the results show that although the random front pyramid texture has a better light absorption in the range of 900?1200 nm than the periodic front texture,the periodic double-sided pyramids texture exhibit almost the same light absorption in the whole range as the random double texture.Besides,the solar cells with double-sided pyramids show extremely low angular dependence of incident light compared with only front textured cells.Thus,the double-sided light trapping structure designed in the present work provides an alternative pathway to improve the performance of ultrathin c-Si cells.Secondly,the finite difference time domain?FDTD?method is used to design and simulate the composite nano-texture silicon cell with the secondary texture based on the nano-cylinder texture.Firstly,the surface of the nanocylindrical texture cell was optimized to obtain the best nanocolumn structure.The photocurrent density of the cell was 72.8%higher than that of the planar reference cell.Next,cylindrical and conical cavities are dug on the basis of the nanocolumn structure,on the basis of comparison,found that nano column combined with conical holes of composite structure can increase the photocurrent density,compared with nano cylindrical structure in the wavelength of 300 nm to 700 nm range on improves the optical absorption of the cell,in comparison with plane reference cell photocurrent density increased by 86.8%.It is proved that the composite structure can significantly improve the optical absorption of ultra-thin crystalline silicon cell within a certain range of parameters,and the distribution of electric field in the cell can be known that the composite structure is more conducive to the transmission of long wavelength incident light to the bottom of the cell.Then,we propose and simulate a perovskite solar cell with a nanoconical and pyramidal antireflective coating texture,and enhance the photocurrent density of the cell through photon management.Through the simulations and optimizations,the achieved maximum photocurrent densities are 24.95 and 24.52 mA/cm² for pyramidal and conical nanotextures made of SiO₂ material,which are 9.3%and 7.5%higher than that of the planar reference cell,respectively.In contrast,when the material of the two nanostructures is replaced with Si₃N₄,the photocurrent densities of the pyramidal and conical nanotextures are enhanced by 12.2%and 12.5%.It is further found that the solar cells with the surface of nanostructures show extremely low angular sensitivity of photocurrent density,which is beneficial to practical applications without the need of sun-tracking installment.Finally,perovskite and crystalline silicon cells with the best parameter structure simulated above are connected in series to construct two kinds of stacked cells.By optimizing the stacked cells,it is found that when the thickness of perovskite absorption layer is 55 nm,the top and bottom cells can achieve a matching photocurrent density of 16.55 mA/cm² and 16.36 mA/cm²,respectively.From the absorption spectra,it can be seen that the top perovskite mainly absorbs sunlight in the short-wave band of 300-800 nm,while the bottom crystalline silicon mainly absorbs sunlight in the long-wave band of 800-1200 nm.The stacked cell designed by us is composed of ultra-thin perovskite absorption layer and ultra-thin crystal silicon absorption layer.It not only reduces the cost of cell manufacturing,but also reduces the content of toxic elements in perovskite absorption layer.It is a main direction for the development of stacked cell in the future.