The effect of etching time of porous silicon On solar cell performance

Silicon is one of the most useful and low cost semiconductor material among others and its technology is the most advanced material, well-developed and least expensive compared to the technology of complex other semiconductor and it is one of the most widespread surrounding materials and one of the most common [1]. Silicon based nanocrystallines/nanoporous are some new photoelectronic and informational materials developed rapidly in recent years. For a long time, silicon has been considered unsuitable for optoelectronic applications because bulk silicon emits hardly any useful light due to its indirect band gap nature [2]. This opinion was deeply changed after the discovery of bright emission from porous silicon (PSi) and nanocrystals [3]. PSi was first discovered in 1956 by Uhlir [4] during silicon electropolishing experiments. Since then not much attention was paid to this PSi layer but from the 1990s it has been under extensive investigation after the discovery of the light emitting properties of nano Psi in the visible region by L. Canham [5], who showed room-temperature photoluminescence of an anodized p-type silicon wafer [6] Porous silicon (PS) layers based on crystalline silicon (c-Si) n-type wafers with (1 0 0) orientation were prepared using electrochemical etching process at different etching times. The optimal etching time for fabricating the PS layers is 20 min. Nanopores were produced on the PS layer with an average diameter of 5.7 nm. These increased the porosity to 91%. The reduction in the average crystallite size was confirmed by an increase in the broadening of the FWHM as estimated from XRD measurements. The photoluminescence (PL) peaks intensities increased with increasing porosity and showed a greater blue shift in luminescence. Stronger Raman spectral intensity was observed, which shifted and broadened to a lower wave numbers of 514.5 cm_1 as a function of etching time. The lowest effective reflectance of the PS layers was obtained at 20 min etching time. The PS exhibited excellent light-trapping at wavelengths ranging from 400 to 1000 nm. The fabrication of the solar cells based on the PS anti-reflection coating (ARC) layers achieved its highest efficiency at 20 13th Annual Electrochemistry Seminar of Iran Materials and Energy Research Center (MERC), 22- 23 Nov, 2017 236 min etching time. The I–V characteristics were studied under 100 mW/cm2 illumination conditions.