Length Scale Dependence of Periodic Textures for Photoabsorption Enhancement in Ultra-thin Silicon Foils and Thick Wafers

TL;DR

This study identifies a universal 1000 nm period inverted pyramidal grating that maximizes photo-absorption in silicon solar cells across various thicknesses, supported by simulations and experimental validation.

Contribution

The paper demonstrates that a 1000 nm periodic grating optimizes photo-absorption in silicon wafers of different thicknesses, enabling uniform fabrication of high-efficiency solar cells.

Findings

A 1000 nm grating period enhances photo-absorption across silicon thicknesses.

Experimental results confirm simulation predictions about reflectance reduction.

The universal grating period simplifies manufacturing of efficient silicon solar cells.

Abstract

In this paper, we simulate a front surface inverted pyramidal grating texture on 2 to 400 micron thick silicon and optimize it to derive maximum photocurrent density from the cell. We identify a one size fits all front grating period of 1000 nm that leads to maximum photo-absorption of normally incident AM1.5g solar spectrum in silicon (configured with a back surface reflector) irrespective of the thickness of the crystalline silicon absorbing layer. With the identification of such universally optimized periodicity for the case of an inverted pyramidal grating texture, a common fabrication process can be designed to manufacture high-efficiency devices on crystalline silicon regardless of wafer thickness. In order to validate the results of the simulation, we fabricated high resolution inverted pyramidal textures on a 400 micron thick silicon wafer with electron beam lithography to compare the reflectance from submicron and wavelength scale periodic textures. The experimental reflectance measurements on textures confirm that a 1000 nm period grating texture performs better than a 500 nm period texture in reducing reflectance, in agreement with the simulations.