Light Trapping Textures Designed by Electromagnetic Optimization for Sub-Wavelength Thick Solar Cells

TL;DR

This paper uses electromagnetic optimization to design nanoscale surface textures that enhance light trapping in sub-wavelength thin solar cells, achieving significant absorption improvements over random textures.

Contribution

It introduces a computational electromagnetic approach to identify optimal surface textures for sub-wavelength solar cells, surpassing random texturing performance.

Findings

Optimized textures achieve ~39x enhancement factor.

Textures outperform random structures by ~30%.

Enhancement approaches but does not reach the 4n^2 limit.

Abstract

Light trapping in solar cells allows for increased current and voltage, as well as reduced materials cost. It is known that in geometrical optics, a maximum 4n^2 absorption enhancement factor can be achieved by randomly texturing the surface of the solar cell, where n is the material refractive index. This ray-optics absorption enhancement limit only holds when the thickness of the solar cell is much greater than the optical wavelength. In sub-wavelength thin films, the fundamental questions remain unanswered: (1) what is the sub-wavelength absorption enhancement limit and (2) what surface texture realizes this optimal absorption enhancement? We turn to computational electromagnetic optimization in order to design nanoscale textures for light trapping in sub-wavelength thin films. For high-index thin films, in the weakly absorbing limit, our optimized surface textures yield an angle- and frequency-averaged enhancement factor ~39. They perform roughly 30% better than randomly textured structures, but they fall short of the ray optics enhancement limit of 4n^2 ~ 50.