Constructing Of Nanostructured Metal Electrodesand Their Applicationsto Solar Cells

The first generation silicon solar cells were fabricated and achieved by the production processing method at the expense of environmental pollution,high energy consumption,despite their high efficiency,they are in disadvantageous state in market competition Compared with the traditional fossil energies due to high power generation cost.Cost reduction is the key whether or not the first generation silicon solar cells obtain competitive advantage in the market.Second generation solar cells have characteristic of mass production in order to reduce costs.Thin film solar cell can not only reduce the use of the absorption material amount,which is suitable to mass production,but also be conducive to the separation and collection of photogenerated carriers,improve the photoelectric conversion efficiency.But the second generation solar cells still have the problem of insufficient light absorption.The third generation solar cells are mainly based on nanostructured solar cells.Some new physical mechanisms are introduced to increase the solar energy conversion efficiency by means of low cost processing or use of low quality absorption material,or some nanostructures etc.The development process of solar cells from bulk materials,film or thin film material to nanostructured materials is also a process to realize the roll-to-roll mass production and production cost reduction.Many problems in the process are essential to resolve.One problem is a bendable transparent conductive electrode compatible with the roll-to-roll mass production;another problem is the insufficient light absorption problem of film or thin film solar cells.According to the above problems,this thesis consists of three aspects:1.The drawbacks of traditional ITO films such as its brittleness and strong absorption in the UV/blue spectral range make them unsuitable to the roll-to-roll mass production in solar cells and LEDs;Nanostructured metal square mesh electrode have favorites such as high optical transparency,good electrical conductivity,mechanical flexibility,easy machining and compatibility with the mass production style.by using the finite-difference time domain method,the effects of the period,linewidth and height of Au square mesh electrode on the spectrum transmittance were firstly analyzed and then Au square mesh TCEs with the 500 nm in period,70 nm in height and line width ranging from 60 to 100 nm were fabricated by using EBL technique.The measured results showed that the optical transmittance of the TCEs is about 70% in the 350-700 nm wavelength range and over 80% in the 700-1000 nm range,which accord with the theoretical simulation results.Optical transmittance is affected by localized surface plasmon resonance?LSPR?,surface plasmon polarizations?SPPs?and the reflection of Au nanostructures.The measured surface resistivity of the TCEs with the 500 nm in period,50 nm in height and 50 nm in linewidth is about 74.5 ?/m2 due to fabrication drawbacks.2.A novel nanostructured Ag crossing grid-ITO composite front electrode with plasmonic light absorption enhancement is designed to resolve inadequate light absorption problem in ultrathin film c-Si solar cells.In this structure,the ultrathin ITO layer is mainly used to collect charge and Ag crossing grids work as a charge transportation path and an optical absorption enhancer.According to the defined absorption enhancement factor G,structural parameters,such as ITO film thickness,linewidth,height and period of Ag grid,were systematically optimized using finite-difference time-domain stimulations,and absorption enhancement mechanisms were analyzed.A 61% light absorption enhancement is observed for the c-Si solar cell with Ag crossing grid in composite front electrode compared to that without Ag crossing grid.Four types of resonance modes such as Fabry–Perot modes,waveguide,localized surface plasmon resonances and surface plasmon polaritons are supported by the designed structure.FP modes may be excited in bare c-Si SCs,but the inclusion of 2D Ag crossing grid introduces waveguide sandwiched by Ag grids and Ag back electrode,SPPs and LSPR modes that lead to enhanced light absorption.3.Nanostructured metal back electrode can couple vertical incident light into surface plasmon polaritons mode with the lateral propagation path and enhance light absorption.In this part,Au regular hexagonal ridge arrays are fabricated using EBL method and are used as nanostructured metal contact electrodes for the Cu₂O-ZnO solar cells in order to enhance light absorption of thin Cu₂ O film.The introduction of nanostructure in back metal contacts results in the deteriorating interface quality so that open circuit voltage cut down.The Only optimized metal nanostructures may be beneficial to LSPR absorption enhancement in thin Cu₂ O absorber.In this structure,SPPs coupling of incident light occur at wavelength larger than 650 nm and do not contribute to the effective absorption of Cu₂ O.According to the existing problems in novel thin film solar cells,one is a technology of the design and fabrication of flexible transparent electrode suitable for the large-scale production;another is the inadequate absorption enhancement in thin film solar cells.Firstly,the theoretical calculation and experimental research are launched on a metal nanostructured transparent electrode.And on this basis,a novel nanostructured Ag grid-Indium Tin Oxide?ITO?film composite front electrode with plasmonic light absorption enhancement is designed through the FDTD calculations.A regular hexagon convex metal nanostructure was prepared by the method of electron beam lithography and their light absorption enhancement in the Cu₂ O solar cells were investigated in details.Optical theory simulation and experiment combination are the main innovation points of this thesis.