Study On Surface Light Trapping Structures For Crystalline Silicon Solar Cells

As a clean and inexhaustible reproducible green energy, photovoltaics (PV) is an important part of the utilization of solar energy and has drawn extensive attention. PV market and corelative application increased drastically. In China, a world-shaking growth of PV industry has been witnessed. The output had been the first in the world since 2007. However, domestic studies on relative science are still short and technology accumulations are relatively devoid. The lack of technology hinders the further development of PV industry. Therefore, basic studies on PV have imperative scientific significance and application value.Presently, crystalline silicon solar cells which accounts for more than 90% of all kinds of solar cells are the dominator of PV market. According to a matter of speculation, crystalline silicon solar cells will still be the dominator of PV market before 2020. Because of the high cost of silicon materials, silicon wafers are getting thinner and thinner for effective cost reduction. Utilization of thin wafer increases the request for light absorption and surface passivation. Light absorption is imperative to keep the property of silicon solar cells stable and to improve conversion efficiency. We have studied influence of subsurface damage on texturing of monocrystalline silicon wafers for solar cells; fabrication of PS layer and control the morphology of PS layer; designation and optimization of porous-pyramid structure. The conclusions are the following:1. "Pyramid" grew irregularly during the texturing process when the subsurface damage is serious. Otherwise, "Pyramid" grew regularly when the subsurface damage is light. Silicon wafer can show fine reflected property when it was textured 60 min in 3wt% KOH and 8vol% IPA alkali solution after reacted at 80℃for 40s in 20wt% KOH solution. The subsurface damage can be removed completely. Reduction of dissipating silicon can be carried out in the chemical etch process.2. Disordered porous silicon layer was obtained on silicon wafer by stain etch in 5 M (M = mol L-1) HF and 0.14 M Fe (NO₃)₃ solutions at 50℃±1℃. Corrosion pits which filled with porous silicon was gained by increasing the etchant to 10M HF and 0.2M Fe (NO₃)₃. Porous silicon changes to pillar-like structures which will increase reflectivity of silicon wafer when oxidant increases from 0.2M to 0.4M.3. Addition of AgNO₃ to HF / Fe(NO3)₃ solution can remarkably improve the uniformity and covering scale of PS layer on silicon wafer because of the deposition of silver particles on silicon surface can attract electrons and accelerate the cathode reaction. Silver particles link with each other will results in formation of silicon nanowires. PS layers were obtained when silver particles are dispersed.4. Both PS layer and SiN_x film can work as anti-reflection coating and reduce surface reflectivity of polycrystalline silicon. PS layers were uniform at wide range of polycrystalline silicon surface. While orderly deep porous texture was formed at the neighborhood of grain boundaries. It's difficult to form uniform PS layers on polished silicon surface without metal catalyst.5. Pyramids were reserved and reflectance property was fantastical when second etching time is 30min during the fabrication process of porous-pyramid texture. Effective lifetime of silicon wafers reduces gradually as etching time increases. After textured for 60 min in KOH/IPA solution, the optimal etching time for silicon wafer is 30 min in 10M HF/0.2M Fe (NO₃)₃ solutions when both reflectance and effective lifetime are considered.6. Pyramid textured silicon wafer etched in HF/Fe (NO₃)₃/AgNO₃ solutions can accelerate the etching reaction and improve the uniformity of PS layers. The reflectivity of porous-pyramid textured silicon is small. The reduction of reaction time can effectively reduce iron contamination.