Optimization of the Surface Structure on Black Silicon for Surface Passivation

Anti-Reflectance Optimization of Secondary Nanostructured Black Silicon Grown on Micro-Structured Arrays

Owing to its extremely low light absorption, black silicon has been widely investigated and reported in recent years, and simultaneously applied to various disciplines. Black silicon is, in general, fabricated on flat surfaces based on the silicon substrate. However, with three normal fabrication methods-plasma dry etching, metal-assisted wet etching, and femtosecond laser pulse etching-black silicon cannot perform easily due to its lowest absorption and thus some studies remained in the laboratory stage. This paper puts forward a novel secondary nanostructured black silicon, which uses the dry-wet hybrid fabrication method to achieve secondary nanostructures. In consideration of the influence of the structure's size, this paper fabricated different sizes of secondary nanostructured black silicon and compared their absorptions with each other. A total of 0.5% reflectance and 98% absorption efficiency of the pit sample were achieved with a diameter of 117.1 μm and a depth of 72.6 μm. In addition, the variation tendency of the absorption efficiency is not solely monotone increasing or monotone decreasing, but firstly increasing and then decreasing. By using a statistical image processing method, nanostructures with diameters between 20 and 30 nm are the majority and nanostructures with a diameter between 10 and 40 nm account for 81% of the diameters.

An Investigation on a Crystalline-Silicon Solar Cell with Black Silicon Layer at the Rear

Crystalline-Si (c-Si) solar cell with black Si (b-Si) layer at the rear was studied in order to develop c-Si solar cell with sub-band gap photovoltaic response. The b-Si was made by chemical etching. The c-Si solar cell with b-Si at the rear was found to perform far better than that of similar structure but with no b-Si at the rear, with the efficiency being increased relatively by 27.7%. This finding was interesting as b-Si had a large specific surface area, which could cause high surface recombination and degradation of solar cell performance. A graded band gap was found to form at the rear of the c-Si solar cell with b-Si layer at the rear. This graded band gap tended to expel free electrons away from the rear, thus reducing the probability of electron-hole recombination at b-Si and improving the performance of c-Si solar cell.

Optical and Electrical Characteristics of Silicon Nanowires Prepared by Electroless Etching

Silicon nanowires (SiNWs) were fabricated by the electroless etching of an n-type Si (100) wafer in HF/AgNO₃. Vertically aligned and high-density SiNWs are formed on the Si substrates. Various shapes of SiNWs are observed, including round, rectangular, and triangular. The recorded maximum reflectance of the SiNWs is approximately 19.2%, which is much lower than that of the Si substrate (65.1%). The minimum reflectance of the SiNWs is approximately 3.5% in the near UV region and 9.8% in the visible to near IR regions. The calculated band gap energy of the SiNWs is found to be slightly higher than that of the Si substrate. The I-V characteristics of a freestanding SiNW show a linear ohmic behavior for a forward bias up to 2.0 V. The average resistivity of a SiNW is approximately 33.94 Ω cm.