Investigation Of Process For Surface Texture Of Multi-crystalline Silicon

Recently the increasing serious environment pollution and energy crisis prompt the rapiddevelopment of solar energy. Crystalline silicon （c-Si） is a material commonly used byterrestrial photovoltaics （PV） industry because of non-toxicity and abundance （25%of theEarth’s crust）. In recent years, the multi-crystalline silicon （mc-Si） has become one of themost important substrate materials for solar-cell applications. It is known that texturizationtechnology can reduce the reflection losses thus overall efficiencies on mc-Si solar-cellapplications can be improved. There has been growing interest in the development of surfacetreatment to enhance light-trapping cells by several methods, such as the use of physicalanti-reflection sputter, reactive ion etcher（RIE）, laser process and acid etching. Among thesemethods, the acid etching for texturing the surface is the major industrial process because ofits low-cost, high etching rate and large-area uniformity. This paper reports the optimizedcondition for crystalline silicon solar cell fabrication, which easily meets the requirement foroptical and electrical performance of solar cells. The main results are as following.（1）The etching rate decreased at first but increased later on with the HNO₃being added. InHF-rich system，low reflectivity surface texture could be obtained, while it was difficult toprint the electrode on the grain boundary when it is deep. In HNO₃-rich system, the surfacereflectivity obtained was higher.（2）There was large difference for reaction rate affecting by temperature as ratio changed inHF-HNO₃-H₂O system. Low-temperature acid etching had more advantages compared toroom-temperature acid etching. Good result was obtained as the HNO₃content decreased atlow-temperature acid etching. The optimum technique for textured structure onmulti-crystalline silicon was as following: HF:HNO₃:H₂O=1:4:2, temperature at3℃andetching rate was2.6μm/min,（3）The acid etching occurred at crystal boundary when activation energy was low. Theetching pit had a large H（depth）/R（width） when the reflectivity reached the minimum. Then H decreased and R increased, the surface morphology tended to be smooth. The reflectancedecreased at first, increased later on. Ultimately it tended to be stabilized.（4）In HNO₃-rich system, stable textured surface and production could be obtained byadjusting the temperature and time to control corrosion weight in a certain range. Worm-liketextures could easily meets the requirement for optical and electrical performance of solarcells, which could achieve the best efficiency. The applied was successfully used in25MWproduction line of multi-crystalline silicon solar cell.