Design, Manufacture And Properties Of The Bionic Light Trapping Functional Sufrace

The optical loss is one of the major obstacles to improve its efficiency of solar cells. Toreduce its surface reflection, there are mainly two ways: one is the use of anti-reflection film; thesecond is the use of light trapping structures. At the same time, as a necessary part of the solarradiation on earth, the ultraviolet (UV,200-400nm) is essential and necessary for life on earth.But exposing in too much UV radiation, then the body will be suffered fatal injuries. Theadvantages and disadvantages of the UV radiation strongly inspired the research interest ofmany research teams to explore and develop the light trapping functional surfaces of spaceequipment. By using reflection, refraction and scattering, light trapping structures scattered theincident light to various angles and thereby increasing the light path in the solar cell, resulting inthe light absorption efficiency is increased significantly. To date, various antireflective structures,such as “honeycomb” surface, sinusoidal grating texture, self-ordered dimple patterns, periodicpyramids, and binary gratings have been extensively studied and developed to enhanceexcellent antireflective efficiency of optical devices. Yet, these optical structures have notachieved an ideal light trapping effect. So, looking forward the ideal light tapping functionalsurface is the hot and difficult areas of photovoltaic research.Inspired from nature, butterfly wings were chosen as a natural model and its features forlight trapping effect were revealed. These butterflies live in a high altitude and high latituderegions, which is a low-temperature of strong ultraviolet environment. It was found that the lighttapping effect is closely related to the ultrahierarchical structures of wing scales. In this paper,three kinds of butterflies with obvious structural color were chosen as natural model. Alcoholdiscoloration experiment determines its structural color characteristics. Using a spectrophoto-meter, the butterfly species with excellent light trapping properties were screened out. Itsmicro-scale structure and light trapping properties were then studied. The optimized3Dconfiguration of the coupling structure was determined using SEM and TEM data. The lighttrapping mechanism of butterfly scales was studied. An optical model was created to check theproperties of this light trapping structure. The simulated reflectance spectra are in concordancewith the experimental ones. Also, the perfect combination of three-dimensional ultrastructure ofbutterfly wings and the complex refractive index of corneum is beyond the capability of currentmanufacturing technology. Although the physical mechanism of light trapping property ofbutterfly wings is well understood, it remains a challenge to create artificial replicas of thesenatural functional structures. Here, a SiO2inverse replica of a light trapping structure in butterflywing scales was synthesized using a method combining a sol-gel process and subsequent selective etching. Using this simple process, the original structures of bio-templates were wellinherited by the structures of the inverse replica. The entire hierarchical structure of butterflywings was successfully retained. These works provide the necessary support for further study ofthe coupling effects between precise structure and the optical effect. In turn, it is possible todesign the high-performance optical components.This paper is divided into seven chapters. The first chapter is an introduction. The majorneeds of the light trapping structures were introduced. Close relations between biologicalfeatures and the surface structures and the latest progress of bionic were also introduced. Allthese introductions fully demonstrated the importance and necessity of the works in this article.The second chapter is the light trapping surface of butterfly and its optical test. The detailedthree-dimensional structure parameters were obtained. Chapter three was the mechanism of theoptical functional surface of butterfly scales. First, the optical model of the light trappingstructure was established using experimental data obtained previously. From the perspective ofthe relationship between the surface structures of the unique features of biology, the opticalmodel was analyzed. Using photonic crystals and diffraction grating theory, the light trappingmechanism of butterfly scales was studied. Chapter four is manufacturing the light trappingfunctional surface by using sol-gel method. A composite sample obtained using sol-gel process.The light trapping surface structure was achieved tunable by external stimulus. Chapter five isthe fabrication of the bionic light trapping surface using the butterfly wings as the bio-template.The intricate light trapping structure was replicated in three steps by a synthetic methodcombining a sol-gel process and subsequent selective etching. The detailed and carefulparametric comparison of the morphology, dimensions and distributions of the extremelysimilar textured micro-structures between the original template and the inverse replica isachieved. Afterwards, it is conformed that the original structures of bio-templates are wellinherited by the structures of the inverse replica. Chapter six is the light trapping study ofreplicated samples. The parametric comparisons of the morphologies and structures between theoriginal template and the replica were carefully conducted, and it was found that the originalstructures of bio-templates were well inherited by the structures of the inverse replica. Chapterseven is the conclusions.Studies of the bionic light tapping surface in this paper will provide a new way ofdesigning new efficient light trapping structures. If this bionic light tapping surfaces could beused in the optical trapping design of solar cells, it is expected to reduce the optical loss, whichhas important application value in improving the light use efficiency of solar cell.