ELSI · Electrochemical Silicon Layers Formation in Fused Salts

Electrochemical Silicon Layers Formation in Fused Salts

The world photovoltaic (PV) electricity production has experienced in recent years an exponential growth. Nevertheless, solar energy conversion still remains relatively costly when compared to the power generated from fossil or nuclear fuels. Cost reduction of photo-electricity, therefore, is high on the agenda of PV engineers and materials scientists. Vast majority of the solar cells are produced from silicon. Bare silicon reflects more than 30 % of the incident light. Silicon surface texturing and coating by antireflection coatings helps to increase efficiency of solar energy harvesting. In particular, so-called black silicon promises an effective approach to reduce the light reflection losses. Most of surface techniques recently applied to obtain silicon textures with efficient light absorbance (femto-second laser engineering, atomic layer deposition, etchings) are too costly and technically sophisticated to be applied in silicon mass production. Furthermore, etching involves toxic and aggressive chemicals, such as hydrofluoric acid, and in certain cases-expensive catalysts. In this project, we invented a new method of silicon surface texturing, which is based on electrochemical silicon surface modification in molten salts. At the heart of the invention is electro-deoxidating of thin silica film precursor. Black silicon was created by this method-a material with nano-micro structures, which effectively absorbs light and shows capability of increasing the efficiency of PV devices. Versatile and novel silicon surface architectures, which effectively absorb light in a wide visible region, were created. The architectures were composed of globular nano-micro networks with pores and nano-fibers. Light absorbance was achieved up to 95 % in the solar spectrum region, which is most useful for solar cells. Light absorbance of the obtained surfaces outperforms that of most surfaces formed by conventional etchings or vacuum-deposition. The invented method is quite simple, rapid and does not involve toxic or aggressive chemicals or hazardous emissions. It has also good scaling-up possibilities for industrial applications. Other advantages of the method include energy efficiency and possibility to control silicon surface morphology and structure depending on the operating conditions. The obtained black silicon, as a porous material, is also attractive in many fields where specifically high silicon surface to volume rates are of importance, for instance, electrochemical batteries and as a platform for various sensors-chemical, biological, pressure, temperature and magnetic. This type of silicon is also attractive in solar-driven generation of hydrogen from water, where the photo-efficiency of silicon electrode is limited by light absorption. The method of silicon surface texturing was protected by International patent application and reported to Cambridge Enterprise Limited-a company commercialising University science. The obtained results open the route for cheaper harvesting of solar energy and contribute to the European scenarios to significantly increase part of solar energy in the total European Union electricity market. The project also contributes to increasing of public awareness in the photovoltaic technology as a provider of clean, sustainable and secure energy from the most abundant source, which is free.

Data: CORDIS, © European Union