Growth rate of AL2O3 Thin Film by Liquid Phase Deposition as an Anti-reflection Coating Layer on Crystalline Silicon for Solar Cell Applications

Abstract

The fabrication of photovoltaic (PV) device requires that surface reflectance of solar cells has to be minimized to achieve higher photo-conversion efficiency (PCE). Antireflection coating layer is deposited on the surface of a p-type crystalline silicon material to reduce the surface reflections of solar radiation and increase its absorption for efficient solar cell application. In this work, aluminum oxide thin film by liquid phase deposition (LPD-Al2O­3) is synthesized from combined solution of aluminum sulfate octadecahydrate (Al2(SO4)3·18H2­O) and sodium carbonate (NaHCO3) with pH of 3.1. Some samples of p-type (100) crystalline silicon (c-Si) wafers of resistivity 1 – 10 mΩ were immersed inside the growth liquid of LPD-Al2O­3 thin film for 1hr – 2.5 hours. This is followed by annealing the samples at a temperature of 450oC, the deposition rate is faster in the range 1 – 1.5 hours is about 35nm/hr. As the growth time increases, the growth rate of the film decreases and remains nearly constant at about 10 nm/hour at 1 – 2 hours. When the growth time exceeds 2 hours, the film thickness remains unchanged showing that the liquid has lost in growth ability. The weighted average reflection (%) of planar c-Si is reduced from 44.9 % to 29.6 % after deposition of the LPD-Al2O­3 for 2.5 hours growth time, indicating a 34.1 % reduction in reflection within wavelength region of 300–1100 nm. While the root means square (RMS) surface roughness of 36.5 nm was also recorded at the highest growth time of 2.5 hours. This shows the effect of thicker LPD-Al2O­3 thin film layer increases the anti-reflecting coating property of the material.