The Research On Ag-Catalyzed Chemical Etching And Its Application In Silicon Splar Cells

Photovoltaic(PV)technology is a clean and green energy technique which can convert the sunlight into the electricity.With the increasing concern on global warming and fossil fuel depletion,PV technology is attracting more and more attention in both academic and industry communities.Silicon-based solar cells are the most mature and the largest-scale cell products in the PV market.At present and for the foreseeable future,silicon-based solar cells continue to dominate the global market for PV generated electricity.Improving efficiency and lowering cost are still the main theme of the development of silicon-based solar cell development,but also the driving force of PV generated electricity to reach grid parity.Improving the optical properties of solar cells is one of the important ways to achieve a high conversion efficiency.In recent years,with the large-scale application of diamond wire sawing(DWS)technology,the cost of silicon wafer has been greatly reduced.However,the DWS multicrystalline silicon(mc-Si)wafer,due to the less surface saw damages and the existence of directional saw marks,is difficult to be textured to obtain an effective trapping texture for its large-scale application.Recently,metal-catalyzed chemical etching(MCCE)technology has been rapidly developed in the PV industry due to its ability to effectively texture the surface of the DWS mc-Si wafers,and the method is simple and the cost is controllable.However,the application of MCCE technology in silicon solar cells still faces many challenges,such as difficult process control,high chemical consumption,unclear internal reaction mechanism,and how to effectively apply it to monocrystalline silicon(mono-Si)solar cells.In this dissertation,controlled etching of silicon surface microstructures based on AgMCCE is systematically studied.Firstly,the internal reaction mechanism and reaction kinetics of Ag-MCCE were presented by studying the characteristics of electroless Ag nanoparticles(AgNPs)deposition on the wafer surface and the characteristics of Ag-MCCE in H2O2/HF system.Then,based on the internal reaction mechanism of Ag-MCCE,a novel idea and reaction kinetics of complementary etching and ozonated deionized water(DIO3)as a hole injection agent were proposed and studied,and the optimized submicron-texture was successfully prepared.Finally,based on the reaction characteristics of Ag-MCCE,the new ways for the preparation of micro-nano hybrid structure and heteroface microstructures were proposed.Most of these research results have been verified and applied in the mass production of multi-and mono-Si solar cells.The main achievements in this research are summarized as follows:1.The characteristics of electroless AgNPs deposition on the wafer surface were studied.the morphologies and influencing factors of AgNPs deposition on wafer surface under different conditions were studied.The results show that low concentration,low temperature,relatively short reaction time and proper amount of HF are more favorable conditions for uniform deposition of AgNPs.Thus,the process based on trace Ag-MCCE is proposed and the cost is greatly reduced.2.The reaction kinetics of Ag-MCCE in H2O2/HF system was studied.The ratio between H2O2 and HF concentration(defined a p value)indicates the process of oxidation and dissolution of Si on the wafer surface,and the reaction kinetics of Ag-MCCE is significantly different under different p systems.The results show that the surface morphology and reflectance of the silicon wafers etched by Ag-MCCE in H2O2/HF system are strongly related to the p value,reaction temperature,etching time,etc.3.Complementary etching behavior between Ag-MCCE and alkali etching was studied.Due to the existence of grains with different orientations on mc-Si surface,either alkali etching or Ag-MCCE leads to obvious differences in both reflectance and appearance on different grains.In this work,a complementary etching technique is proposed to solve the problem,so as to realize the preparation of mc-Si solar cells with no obvious grains in appearance.The results show that the color difference among the grains can be eliminated and the appearance of the mc-Si solar cells is uniform by using the optimized complementary etching process.In addition,the cells fabricated using this texturing method and as-prepared module have better electrical properties and higher outdoor power yield.4.DIO3 instead of H2O2 as a hole injection agent in Ag-MCCE process was studied.Through the optimization on DIO3/HF system,the average efficiency of the as-fabricated mc-Si PERC cells was 0.58%abs higher than those with the conventional acid-textured micron-texture.The results show that it is feasible in principle and technology to use DIO3 instead of H2O2 as an oxidative agent in Ag-MCCE process.In particular,the plasma discharge technology is used to prepare DIO3 in real time,which is simple,low cost and has the potential for large-scale application.5.The application of Ag-MCCE technology in mono-Si silicon cells was studied.The main purpose of this study was to fabricate the nano-scaled structures on alkali-textured micron-scaled pyramid-structures by Ag-MCCE technique.The deposition characteristic of Ag nanoparticles on micron pyramid-structures and its influence on the uniformity of nanostructure were studied,as well as on performance of the mono PERC solar cells.The results show that the distribution uniformity of Ag nanoparticles deposited on the micron pyramid-structures can be improved by using polyvinylpyrrolidone(PVP)as an additive.The prepared nanostructures were uniformly distributed on the micron pyramid-structures.The average efficiency of the as-fabricated mono-Si PERC cell was 22.22%,which was 0.46%abs higher than that of the control group without the additive.The all-angled light trapping property for silicon solar cells can be realized by forming the unique nano-onmicron texture(NOM-texture).6.A solid strategy to realize heteroface microstructures for mono-Si wafer was studied.In order to meet the requirements of mass production in PV industry,a patented Ag-MCCE technology based on back-to-back wafers lamination was proposed and developed.We have successfully fabricated heteroface microstructures on mono-Si wafer,in which a honeycomb-structured light-trapping texture was formed at the front while a polished surface was formed at the back.The results show that the average efficiency of the as-fabricated mono-Si PERC cells is 0.12%abs higher than that of the conventional mono-Si PERC cell,which is mainly due to better rear passivation effect and lower recombination loss in the space charge region.In addition,the honeycomb-structured texture is less sensitive to the incidence angle of the light,and also has a good full-angled light-trapping performance.