Design And Performance Of Si-based Micro/Nano Structure Solar Cells

After decades of development,silicon-based(Si-based)solar cells have become the mainstream products in the photovoltaic market.In the face of diversified photovoltaic application scenarios,such as miniaturization,light transmission,flexibility,lightweight and low-cost applications in micro energy self supply,building integration and so on,it is necessary to develop new Si-based photovoltaic to meet the current application needs.This dissertation takes Si Micro/Nano structure solar cells as the research object,focuses on the optical design of Micro/Nano structure and the photoelectric performance of devices,and provides theoretical support for the flexibility,light transmission and low cost of Si-based photovoltaic.The main research work is as follows:(1)Simulation of photoelectric performance of solar cells based on single Si nanowire(SiNW).A trilobal SiNW with multiple equivalent scales is designed.One equivalent scale corresponds to a specific spectral response range,and the wide spectral response of a single SiNW is realized.Each equivalent scale has a vertical distance equal to the height of the SiNW,which ensures the intensity of the response peak and enhances the light capture ability of a single SiNW.Then,it is proved that trilobal SiNWs have good tolerance to the angle and polarization direction of incident light,and are suitable for photovoltaic field.The simulation results show that the apparent short-circuit current density(Jsc)of a single trilobal SiNW solar cell can reach 487.21 mA·cm-2 and the apparent conversion efficiency(η)is 207.49%.Trilobal SiNWs improved the narrow response spectrum of a single SiNW,and have the potential of photovoltaic miniaturization.(2)Research on SiNW morphology design of SiNW array solar cells.Using discrete dipole approximation theory,it is found that the extinction performance of SiNWs is related to the scale of SiNWs in the polarization direction of incident light.According to this discovery,five kinds of SiNWs were designed,and finally a trilobal SiNW with top view was obtained,which improved the extinction ability of a single SiNW by 85%,which is suitable for SiNW arrays most.In addition,according to the comprehensive equation of spectral response of SiNWs,a kind of helical SiNW is designed.The influence of tree independent and controllable characteristic scales in SiNWs on the scattering spectrum is further studied,and the double response peaks with adjustable position are obtained,which can realize the full coverage of the optical band gap of Si materials.A translucent helical SiNW array solar cell with PEDOT:PSS/SiNW array-PDMS/ITO structure is designed.Compared with the cylindrical SiNW array solar cell,the average absorptivity is increased by 40.02%,ηincreased by 54.38%.This provides SiNWs with excellent performance and design ideas for SiNW array solar cells.(3)Optimization design of PEDOT:PSS film in Si-based hybrid solar cells.PEDOT:PSS is an important material to form undoped heterojunction with Si.which has an important impact on light absorption and heterojunction performance.Based on the theory of optical admittance and equivalent interface formula,the solar cell is managed by adjusting PEDOT:PSS film.The maximum effective light absorption is realized by using the periodic variation of reflectivity with wavelength and considering the influence of parasitic absorption of PEDOT:PSS film.By optimizing the photoelectric performance of PEDOT:PSS/Si heterojunction,the light loss is reduced to 18.6%,and the best carrier separation efficiency is achieved at PEDOT:PSS/Si interface.In the steady state,the hole concentration at the heterojunction interface is adjusted to 8.33 ×1012 cm-3,and the optimal η is 12.349%.On this basis,the SiNW arrays were prepared.PEDOT:PSS and SiNWs were studied as composite films,and the changes of open circuit voltage(VOC),Jsc and filling factor(FF)of solar cells were explored.This provides a theoretical basis for the performance regulation of PEDOT:PSS/Si heterojunction and the preparation of Si-based hybrid solar cells.(4)Research on the flexibility of ultra-thin Si wafer and the photoelectric characteristics of solar cells.The law of mechanical flexibility of ultra-thin Si wafer is obtained in the experiment.Through Kirchhoff hypothesis and finite element simulation results,it is proved that PDMS film can effectively reduce the stress concentration on the Si surface and reduce the probability of Si wafer rupture caused by surface stress.The equivalent refractive index of PDMS film with Micro/Nano structure is analyzed by using the equivalent medium theory.It is proved that PDMS film can effectively reduce the reflectivity of Si surface.The calculation model of ultra-thin Si solar cell is constructed,and the mechanical,optical and electrical performance parameters are obtained.The simulation results show that the PDMS film with moth-eye structure can reduce the maximum surface stress of ultra-thin Si solar cell by 33.4%,increase the total light absorption by 42.3%.and the conformal PDMS film can reduce the maximum surface stress of Si pyramid by 71.19%.and η is 19.04%.This theoretically solves the compatibility between flexibility and light absorption of ultra-thin Si solar cells.