Influence of fractal and multifractal morphology on the wettability and reflectivity of crystalline-Si thin film surfaces as photon absorber layers for solar cell

Abstract

Crystalline Si films incorporated with Al are important for applications in microelectronics and solar cells. In this paper, we report on the morphology of crystalline Si surfaces in Al/amorphous-Si bilayer thin films under ion beam irradiation at 100 °C. Micro-Raman and transmission electron microscopy studies show that best crystallization is achieved at a fluence of 1 × 1012 ions cm−2. The contact angle of Si surfaces (after chemically etched unreacted Al), referred to as absorber surfaces, decreases with increasing ion fluence. These surfaces are hydrophobic in nature and the hydrophobicity decreases with increasing ion fluence. Fractal and multifractal analysis of atomic force microscopy images, along with system energy/unit cell and Laplace pressure calculations, supports our observations. Moreover, the calculated multiple scattering cross sections of light, along with reflectivity measurements, indicate that absorber surfaces of best crystalline films have the lowest reflectivity. The present results suggest that such surfaces having low optical reflectance and a hydrophobic nature can be used as photon absorber layers for advanced solar cell devices.

Micro‐morphological investigations on wettability of Al‐incorporated c‐Si thin films using statistical surface roughness parameters

“…The ion irradiation on c‐Al/ a ‐Si films resulted the crystallization of Si in bilayer films, and the top unreacted Al layer were chemically etched off by wet selective etching. The crystallization of Si in c‐Al/a‐Si system under ion irradiation at temperature 100°C and the formation of Al‐incorporated c‐ Si or homogeneous c ‐Si thin film (i.e., absorber layer) were confirmed by transmission electron microscopy (TEM) and electron‐dispersive x‐ray (EDX) analysis, which are discussed in our previous work 28–30 . The crystallization process can be discussed via diffusion mechanism.…”

“…The crystallization process can be discussed via diffusion mechanism. During ion irradiation, the Si atoms diffused along the grain boundary of the, Al layer and after a sufficient accumulation of Si atoms at the grain boundary, the nucleation started and growth occurred 28–30 . In the following sections, we are presenting a new level of topographical understanding and wettability property of the absorber surfaces with the help of 3D surface topography, statistical parameters analysis, and contact angle measurements.…”

“…In order to prepare c‐Al/ a ‐Si interface, 50‐nm thin Al films were deposited on the top of a ‐Si films using thermal evaporation without breaking the vacuum. The as‐prepared Al (50 nm)/ a ‐Si (150 nm) bilayer films were then irradiated at a temperature of 100°C by 100 ‐MeV Ni +7 ions with different fluences of 1 × 10 12 ions‐cm −2 , 5 × 10 12 ions‐cm −2 , 1 × 10 13 ions‐cm −2 , and 5 × 10 13 ions‐cm −2 using 15 UD Pelletron accelerator facility of Inter University Accelerator Center (IUAC), New Delhi, after estimating the range of ions by Stopping and Range of Ions in Matter (SRIM) simulation code 28–31 . The ion irradiation resulted the crystallization of Si in bilayer films and the top unreacted Al layer were chemically etched off by wet selective etching using “Aluminum Etchant‐Type A” (Sigma‐Aldrich) solution.…”

“…The 3D surface topography of thin films possesses only statistical self‐similarity, which takes place only in a restricted range of the spatial scales 10 . In our previous work, we have studied the surface properties of Al incorporated c ‐Si and/or homogeneous c ‐Si layer (such as absorber layer for solar cell) produced at low temperature by a selective way of ion beam irradiation followed by chemical etching in the light of fractal and multifractal concept 28 . However, the statistical parameter's dependent wettability property of these absorber surfaces with the help of 3D surface topography, statistical parameters analysis, and contact angle may give new insight of the subject.…”

“…In order to obtain this absorber layer, the as‐prepared c ‐Al (50 nm)/ a ‐Si (150 nm) (i.e., pristine) thin films are irradiated at a temperature of 100°C using 100‐MeV Ni +7 ions with the fluences of 1 × 10 12 ions‐cm −2 , 5 × 10 12 ions‐cm −2 , 1 × 10 13 ions‐cm −2 , and 5 × 10 13 ions‐cm −2 . The ion irradiation on c ‐Al (50 nm)/ a ‐Si (150 nm) leads to the crystallization of Si in bilayer film 28–30 . In order to expose the absorber layer, remaining Al from the top layer of the bilayer samples is selectively etched‐off.…”