The role of front and back electrodes in parasitic absorption in thin-film solar cells

Mathieu Boccard,Michael Stuckelberger,Fanny Meillaud,Matthieu Despeisse,Peter Cuony,Franz-Josef Haug,Simon Hänni,Christophe Ballif

doi:10.1051/epjpv/2014006

Mathieu Boccard, Michael Stuckelberger + Show 6 more

Open Access

https://doi.org/10.1051/epjpv/2014006

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Abstract

When it comes to parasitic absorption in thin-film silicon solar cells, most studies focus on one electrode only, most of the time the substrate (in n -i -p configuration) or superstrate (in p -i -n configuration). We investigate here simultaneously the influence of the absorption in both front and back electrodes on the current density of tandem micromorph solar cells in p -i -n configuration. We compare four possible combinations of front and back electrodes with two different doping levels, but identical sheet resistance and identical light-scattering properties. In the infrared part of the spectrum, parasitic absorption in the front or back electrode is shown to have a similar effect on the current generation in the cell, which is confirmed by modeling. By combining highly transparent front and back ZnO electrodes and high-quality silicon layers, a micromorph device with a stabilized efficiency of 11.75% is obtained.

Highlights

Minimizing the absorption of non-photoactive layers is of crucial importance for most solar cell technologies
When it comes to parasitic absorption in thin-film silicon solar cells, most studies focus on one electrode only, most of the time the substrate or superstrate
We focus in the following on micromorph tandem cells, which consist of a hydrogenated amorphous silicon (a-Si:H) top cell and a hydrogenated microcrystalline silicon bottom cell

Summary

Introduction

Minimizing the absorption of non-photoactive layers is of crucial importance for most solar cell technologies. In the case of thin-film silicon technology, parasitic absorption due to non-active layer has been identified as a major limitation for present devices [6, 7]. We separate the influence of parasitic absorption in the front and back electrodes by using ZnO in both cases. Two different doping levels are compared for both electrodes, leading to four possible combinations of front and back electrodes. The sheet resistance is kept identical in all cases, and the light-scattering properties of all front electrodes are identical as well. Both electrodes are shown to have similar influence in the NIR spectrum range, which is confirmed by simulations

Experimental details

Results and discussion

Modeling

Conclusion