Optical Insights into Enhancement of Solar Cell Performance Based on Porous Silicon Surfaces

Abstract

The amount of light reflection from the surface is the main obstacle in efficient solar cell performance because reflection is related to the refractive index of the material. For instance, the silicon (Si) refractive index is 3.5, (which can rise by up to 35%), which prevents an electron-hole pair from being generated and could reduce the efficiency of photovoltaic converters. Antireflection coatings ARC are able to reduce surface reflection, increase conversion efficiency, extend the life of converters, and improve the electrophysical and characterization of photovoltaic converters [1]. Porous Si (PS) is attractive in solar cell applications because of its efficient ARC and other properties such as band gap broadening, wide absorption spectrum, and optical transmission range (700–1000 nm). Furthermore, PS can also be used for surface passivation and texturization [2–6]. The potential advantages of PS as an ARC for solar cells include surface passivation and removal of the dead-layer diffused region. Moreover, PS is able to convert higher energy solar radiation into spectrum light, which is absorbed more efficiently into bulk Si [7]. The vibrations, electronic, and optical properties of PS have been studied using various experimental techniques. Of these, the electrochemical etching process is a promising technique for fabricating PS [8–11]. According to the quantum confinement model, a heterojunction can be formed between the Si substrate and porous layers because the latter has a wider band gap (1.8–2.2 eV) compared with crystalline Si (c-Si) [12]. Recently, Ben Rabha and Bessais [13] used chemical vapor etching to perform the front PS layer and buried metallic contacts of multicrystalline silicon solar cells to reduce reflectivity to 8% in the 450–950 nm wavelength range, yielding a simple and low-cost technology with 12% conversion efficiency. Yae et al. [14] deposited fine platinum (Pt) particles on multicrystalline nSi wafers by electroless displacement reaction in a hexachloroplatinic acid solution containing HF. The reflectance of the wafers was reduced from 30% to 6% by the formation of porous layer. Brendel [15] performed electrochemical etching of PS layer into the substrate based on homoepitaxial growth of monocrystalline Si films, yielding a module efficiency of 10%. The present work aims to investigate the effect of PS on performance of Si solar cells. Optical properties such as refractive index and optical dielectric constant are investigated.