This is because of enhanced injection of positive holes (h+) into Si and removal of oxidized Si with the increasing etchant concentration [11, 15]. As shown in the insets of Figure 4b, ARS-1620 in vitro the Si nanostructures

fabricated using high etchant concentration (e.g., 33%) exhibit severely rough morphology due to excessively high etchant concentration. Although the Si nanostructures fabricated with etchant concentration higher than 25% exhibited a low SWR value of <3% in the wavelength range of 300 to 1,100 nm, the rough morphology is not favorable for practical solar cell applications [10]. From this point of view, the etchant concentration is also very important for obtaining a desirable surface morphology and height of Si nanostructures. Therefore, the etchant concentration of 20% is considered as a potential candidate to produce Si nanostructures for solar cell applications because this condition

can produce Si nanostructures with smooth etching profile and a low SWR value of 6.39% in the wavelength range of 300 to 1,100 nm. Figure 4 Measured hemispherical reflectance spectra of Si nanostructures and estimated average height and calculated EX 527 in vitro SWRs. (a) Measured hemispherical reflectance spectra of the corresponding Si nanostructures fabricated using different etchant concentrations from 33% to 14% in an aqueous solution. (b) Estimated average height and calculated SWRs as a function of the concentration of etchant. The insets show 45° tilted-view SEM images for etchant concentrations of 20%, 25%, and 33%. The etching temperature of MaCE is also an important parameter for obtaining Si nanostructures with proper morphology and etching rate. Figure 5 shows the antireflection JNK-IN-8 order properties of Si nanostructures as a function of etching temperature. The insets exhibit 45° tilted-view SEM images of the corresponding Si nanostructures. In this experiment, an aqueous solution containing HNO3, HF, and DI water (4:1:20 v/v/v) was used. The average height of the

Si nanostructures SPTLC1 increased from 308 ± 22 to 668 ± 94 nm by elevating the etching temperature from 23°C to 40°C. This result originates from the promotion of carrier diffusion, oxidation, and dissolution during the Si MaCE process at elevated temperature [11, 15]. It is observed that the morphology of Si nanostructures is more rough as the etching temperature elevates over 30°C. Although the hemispherical reflectance spectra of the Si nanostructures fabricated using an etching temperature higher than 30°C exhibited lower reflectance and SWR (<1.10%) than the one with an etching temperature of 23°C, they are undesirable for solar cell applications because of their rough morphology. Therefore, careful attention to the etching temperature for Si MaCE is required to produce proper Si nanostructures for device applications. Figure 5 Hemispherical reflectance spectrum measurement of Si nanostructures.