In this work, we utilize electrochemical impedance spectroscopy (EIS) to study the electronic characteristics of nanostructured silicon (Si) fabricated using the metal-assisted chemical etched (MACE) process. The nanostructured Si fabricated using the MACE process results in a density graded surface that reduces the broadband surface reflection of Si making it appear almost black, which coins it the name ‘black Si’ (bSi). We study two bSi samples prepared using varying MACE times (20s and 40s) and a reference bare silicon sample using EIS between 1 MHz and 1 Hz frequencies. At an illumination intensity created with the use of a tungsten lamp source calibrated to output an intensity of 1-Sun (1000 W/m2), the impedance behavior at bias potentials in both the forward and reverse bias ranging between -1 V and 1 V are studied. We also study the effect of illumination wavelength by using bandpass filters at 400 nm and 800 nm. The results indicate that the charge transfer resistance (Rct) decreases as the surface roughness of the electrodes increases and as the illumination wavelength increases. We also find that the constant phase element (CPE) impedance of the electrodes increases with increasing surface roughness. These results will guide our future work on high efficiency bSi solar cells.
Wenqi Duan and Fatima Toor, "Surface characterization of nanostructured 'black silicon' using impedance spectroscopy," Proc. SPIE 9927, Nanoengineering: Fabrication, Properties, Optics, and Devices XIII, 992711 (Presented at SPIE Nanoscience + Engineering: August 31, 2016; Published: 15 September 2016); https://doi.org/10.1117/12.2237093.
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