Texture engineering of mono-crystalline silicon via alcohol-free alkali solution for efficient PERC solar cells

Control of texture structures is an effective method to reduce surface reflectivity and enhance the efficiency of solar cells. In this paper, pyramid structures are prepared on mono-crystalline silicon wafers by cyclodextrin as surfactant to slow down the etching rate in alcohol-free alkali solution. Compared with volatile alcohol surfactant (e.g. isopropanol, IPA), the cyclodextrin not only possesses a relative high boiling point (1534.4 ℃), but displays non-toxic and biodegradable properties. Furthermore, the surface morphology, average reflectivity, surface recombination of mono-crystalline silicon wafers were studied in detail. The results show that cyclodextrin can decrease the size and depth of pyramid structures, and thus a lower average reflectivity of 7.5% was obtained. In addition, ray tracing simulation was performed to calculate the photo-generated carrier concentration of PN junction with different sizes of pyramids, and the conclusion is that the carrier concentration of small pyramids is much higher than that of large pyramids. Finally, the average efficiency of large-area mono-crystalline silicon PERC solar cells fabricated by cyclodextrin surfactant was 22.69%, which was 0.43% absolutely higher than that of conventional IPA surfactant.