Light Trapping in Schottky Junction Silicon Inverted Pyramid Array in UV-VIS-NIR Range

Abstract

Silicon exhibits transparency in the infrared (IR) range, with its absorption edge occurring around 1100 nm. It signifies that it does not absorb photons with wavelengths beyond its absorption edge, which typically occurs around 1100 nm. As a result, nearly half of the solar spectrum, consisting of near-infrared (NIR) range photons, remains unabsorbed by silicon based solar cells. If this range of photons can be absorbed by engineering the structure, a huge improvement in the short circuit current density will be achieved and it ultimately increases the efficiency of solar cells. In this report, we engineer the silicon structure in combination with random inverted pyramid arrays and a thin layer of gold to efficiently absorb the NIR solar spectrum. Moreover, harnessing NIR photons for absorption can enhance the efficiency of solar cells beyond the conventional Lambertian limit. To achieve this goal, we employed a novel approach involving arrays of random inverted pyramids on silicon covered with a thin gold film. These structures demonstrated significant light absorption in the IR spectral range, specifically below the bandgap of silicon. We initially optimized the fabrication process for random inverted pyramids using metal-assisted chemical etching. Subsequently, we coated selected inverted pyramid samples with gold films of varying thicknesses. Through thorough UV-NIR analysis, we identified a thin coating of gold can result in a significant reduction of reflectance and increment of absorbance, reaching up to 64% in the NIR range. Furthermore, the short-circuit current density theoretically obtained for this gold coated inverted pyramid sample is ~ 43.8 mA/cm². We also calculated other important parameters of the solar cell and found that the theoretical efficiency can be enhanced by up to 22% without the incorporation of the surface passivation effect. This study demonstrates the effectiveness of utilizing inverted pyramid structures with a thin gold coating to enhance infrared absorption in silicon-based solar cells. The findings pave the way for the development of high-performance solar cells that can harness a broader spectrum of sunlight, leading to improved energy conversion efficiency.