Impact of the refractive index on coupling structures for silicon solar cells

Laura Stevens,Oliver Höhn,Mario Hanser,Claas Müller,Benedikt Bläsi,Stefan Glunz,Nico Tucher

doi:10.1117/1.jpe.11.027001

Abstract

Structured surfaces are used to reduce reflection and enhance light-trapping in silicon solar cells. In this simulation study, we investigated the relationship between the refractive index of front-side coupling structures on top of planar wafer-based crystalline silicon solar cells and the light-trapping performance of the structures. A crossed diffraction grating with a period of 1 μm and random pyramid structures with varying refractive indices were considered. Simulations were carried out both at the cell level and at the complete module stack level. It is shown that the single pass light path enhancement factor (LPEF) only provides a rough estimate of the light-trapping properties. The light-trapping behavior can only be reliably assessed in the complete system level and these results deviate from the estimated single pass LPEF. It can also be shown that the refractive index of the structure strongly influences the light-trapping behavior.

Highlights

The enhancement of light absorption in wafer-based crystalline silicon (Si) solar cells can be achieved by reducing the reflection and by increasing the light-trapping in the solar cell
We focus on the influence of the refractive index of the structured layer on the light-trapping behavior of wafer-based crystalline silicon solar cells and modules
E.g., at the Lambertian scatterer the single pass light path enhancement factor (LPEF) doubles in the refractive index range from 1 to 3.5, and the system LPEF increases in this range by a factor of 20

Summary

Introduction

The enhancement of light absorption in wafer-based crystalline silicon (Si) solar cells can be achieved by reducing the reflection and by increasing the light-trapping in the solar cell. The state-of-the-art technique for reducing the reflection and induce light-trapping in solar cells involves a combination of a coupling structure with an antireflection coating on the front side of the device.[1] These coupling structures are mostly realized by wet chemical etching, which results in random pyramids on monocrystalline silicon solar cells[2] and in the so-called isotexture[3] on multicrystalline silicon solar cells. An alternative to etching a coupling structure into silicon is the patterning of another material on top of the planar wafer. An optically structured but electrical planar front side of a solar cell has advantages such as less recombination losses, while achieving nearly the same optical performance. Using a high-index material for pillar-like coupling structures on top of a planar silicon substrate was among others presented by Spinelli et al.[7,8]

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Conclusion