(b) Incidence-angle-dependent reflectance as a function of AOI and wavelength for the Si nanostructures fabricated using condition (i). Figure 7a shows the photographs of bulk Si (left) and antireflective black Si (right) fabricated using the optimum MaCE condition. The bulk Si reflects the background image due to its high surface reflection. In contrast, the antireflective black Si does not reflect anything due to its excellent antireflection characteristics. Figure 7b shows the photographs of water droplets with

a contact angle (θ c) on the surface of bulk Si (left) and antireflective black Si (right). The contact angles of a water droplet were measured using a contact angle measurement system (Phoenix-300 Touch, SEO Co., Ltd., Suwon, South Korea). The bulk Si exhibited a hydrophilic surface with the contact angle of approximately 31°, whereas the antireflective black Si exhibited a hydrophobic surface with the contact angle of approximately KU-60019 102°. These surface wetting results may be explained by the Cassie-Baxter model [23]. It is known that the hydrophobic surface provides a H 89 in vitro self-cleaning function, leading to the removal of accumulated dust particles from the surface of solar cells in real environments [19]. Therefore, the Si solar NSC23766 supplier cells with antireflective

nanostructures fabricated by the Si MaCE process can achieve much improved efficiency and maintain their early efficiency longer than one with a flat surface. Figure 7 Photograph and water droplets with a contact angle. Masitinib (AB1010) (a) Photograph and (b) water droplets with a contact angle for bulk Si substrate (left) and antireflective Si (right) fabricated by an optimum Si MaCE condition, respectively. Conclusions We investigated the influence of Si MaCE conditions, including the concentration of HNO3, HF, and DI water as well as etching temperature, on the morphologies and optical properties of the fabricated Si nanostructures to achieve the optimum Si MaCE condition, resulting in desirable antireflective Si

nanostructures with self-cleaning function, for practical solar cell applications. The optical properties of the fabricated Si nanostructures were strongly correlated with Si MaCE conditions. The Si nanostructures fabricated by an optimum MaCE condition demonstrated the extremely low SWR of 1.96% and an angle-dependent SWR of <4% up to an AOI of 60°, compared to that of bulk Si (SWR, 35.91%; angle-dependent SWR, 37.11%) in the wavelength range of 300 to 1,100 nm, as well as a hydrophobic characteristic with a water contact angle of approximately 102°. These results provide improved understanding of Si MaCE and guidelines to achieve desirable antireflective Si nanostructures with self-cleaning capability for high-efficiency c-Si solar cells. Acknowledgements This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MEST) (no. 2011–0017606). References 1.