Preparation Of Single Crystal Silicon Suede For Solar Cells

In order to manufacture the high efficiency of silicon solar cells, the light reflectivity of silicon surface of should be reduced to a minimum. Surface morphology of silicon wafer fully reduced surface reflectivity. The surface reflectivity of Solar cells is an important factor of affecting solar cells light conversion efficiency. This structure can enhance the efficiency of the solar cell because using anisotropic etching silicon surface results in the increase of the absorptivity of incidence light. Therefore, the silicon surface corrosion have the important meaning.to increase solar cells'efficiency.Most people who come from domestic and foreign researched that alkaline solution etch monocrystalline silicon surface. Such as Xi zhenqiang' sodium phosphate, Yang zhiping'sodium silicate, Nishimoto'sodium carbonate and sodium bicarbonate'intermixture, You'solution TMAH and so on.but the experimental reproducibility is poor, meanwhile, there have the insufficiency of high cost and big pollution. For the polysilicon, it is etched with acid etching solution, but the ratio of the acid solutions and different reaction conditions. Therefore, the silicon surface corrosion research has been attracted great attention.In this thesis, by changing the concentration of chemical additive isopropyl alcohol solution, studying the surface morphology'influence on the silicon wafer, it discovered that the isopropyl alcohol solution takes as the chemical additive of sodium hydroxide sculpture solution, it is important to the etch crystalline silicon solar cell surface, the conventional solution of NaOH+IPA (isopropyl alcohol) etch crystalline silicon wafer by adding 0.5wt% and 0.3wt% CH3COONa solutions,Na2Si03 solutions,Na2CO3 solutions, respectively. Sodium acetate solution corrose the single crystal silicon solar cells. The main work summary is as follows: (1) The surface of p-type (100) oriented crystalline silicon wafer are texturized to reduce the surface reflectance. The mixed solution with a concentration of 3wt% sodium hydroxide (NaOH) and adding different concentration of isopropyl alcohol (IPA) were used to etch the surface of crystalline silicon wafer at 80℃for 40 min in our experiments. The results showed that we obtain the best surface morphology with a sufficient low reflectivity of 10.42% when adding 8wt% IPA to 3wt% NaOH solutions between 700 and 900nm. Under the above conditions, a average reflectivity of 11.22%and 14.27% were obtained by adding 0.5wt% and 0.3wt%Na2CO3 solutions, respectively. By adding 0.5wt%Na2CO3 solution, the change of the reflectivity was very small. But, when adding 0.3 wt%Na2CO3 solution, the average reflectivity of texturing surface has a bigger increase, and it was not good to form a pyramid surface morphology.(2)This text based on orthogonal experimental optimation of surface texturization of monocrystalline silicon for solar cell which obtained the optimative theory plan of surface etching,with experimental verification.the most superior theory plan is:the mixed solution with a concentration of 1.5wt%sodium hydroxide(NaOH) and adding a concentration of 5wt% isopropyl alcohol and the concentration of 4wt%sodium silicate were used to etch the surface of crystalline silicon wafer at 85癈 for 25 min in the experiments, and obtain the best surface morphology with a sufficient low reflectivity of 11.07%.By using experiment to verify its theory, it obtain the best surface morphology with a sufficient low reflectivity of 12.98%, this experiment was permitted in error to the extent consistent with the basic theory. In addition, the mixed solution with a concentration of 3wt%sodium hydroxide (NaOH) and adding a concentration of 8wt%isopropyl alcohol (IPA) were used to etch the surface of crystalline silicon wafer at 80癈 for 40 min in our experiments. Under the above conditions, by adding 0.3wt%and 0.5wt%sodium silicate, the results discovered that it can obtain evenly reduces the reflection fabric surface, and compared with adding sodium silicate solution with no flock produced more surface morphology, found that the presence of sodium silicon has provided more starting point for the experimental response, and the fabric surface arrangement is closer. But 0.5wt% sodium silicate solution can provide the more coring beginnings point compared with 0.3wt% sodium silicate solution in the experiment, the arrangement is more closer.(3) The surface of p-type (100) oriented crystalline silicon wafer are texturized to reduce the surface reflectance. In this experiment, a new type of etchant, sodium acetate (CH3COONa) solution, which is used to corrose the single crystal silicon solar cells. In our experiments, by changing temperature and corrosion time, the different concentration of sodium acetate (CH3COONa) solution etch crystalline silicon wafer. The experiment discovered that it can form the good surface morphology by etching crystalline silicon wafer with sodium acetate (CH3COONa) solution. we obtain the best surface morphology with a sufficient low average reflectivity of 12.14% between 700 and 1000nm when adding 20wt% sodium acetate (CH3COONa) solution at 95℃for 40 min in our experiments. Considered from experimental results and cost, this etchant has a lot of advantage, such as low cost, no pollution and good reproducibility, so it is suitable for the large-scale industrial etching.(4) The surface of p-type crystalline silicon wafers in the<100> direction were texturized to reduce the surface reflectance for solar cells. In this experiment, we investigated different texturing process by adding low concentrations CH3COONa, Na2Si03, Na2CO3 solutions to conventional solutions of NaOH+IPA (isopropyl alcohol), respectively. As a result of experiments, we found that by adding CH3COONa and Na2CO3 solutions to mixing texturing solutions of NaOH+IPA, respectively, the average reflectivity of texturing surface do not decrease,but by adding Na2SiO3 solution, the average reflectivity of texturing surface reduces and achieve a regularly shaped pyramid surface morphology. Therefore, a better surface texturing method was found by adding a low concentration of Na2SiO3 solutions to the conventional mixing solutions of NaOH+IPA with a low surface reflectivity and best surface morphology for Si solar cells.