# Disordered nanostructures for light trapping in tandem solar cells

Laura de Almeida, Inès Revol, Jean Baptiste Doucet, Mathieu Arribat, Guilhem Almuneau, Stéphane Collin

► To cite this version:

Laura de Almeida, Inès Revol, Jean Baptiste Doucet, Mathieu Arribat, Guilhem Almuneau, et al. Disordered nanostructures for light trapping in tandem solar cells. Journées Nationales du Photo-voltaïque, Dec 2024, Dourdan, France. 2024. [hal-04958286](https://hal-04958286v1)

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Submitted on 20 Feb 2025

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# Disordered nanostructures for light trapping in tandem solar cells

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L. DE ALMEIDA¹, I. REVOL¹, J-B. DOUCET¹, Mathieu ARRIBAT¹, G.ALMUNEAU¹, S. COLLIN²

¹LAAS-CNRS, Laboratoire d'analyse et d'architecture des systèmes, 31400 Toulouse, France

²C2N, Centre de Nanoscience et de Nanotechnologie, 91120 Palaiseau, France

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C2N

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## Nanostructuration and disorder

Light trapping is an important pathway in photovoltaic devices development that aims to maximize the absorption of light in a material. Increasing the optical path length of light in a material increases the probability of absorption.

As an alternative to light trapping using periodic nanostructures, disordered correlated or amorphous nanostructures have proven to improve diffusion at various angles, to promote light trapping and allow to reduce production cost by increasing tolerance to fabrication defects.

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Absorption spectrum of two-dimensional structures of a-Si layer of 100 nm
The absorption of the **amorphous** structure is better than the absorption of the **periodic** and **random** structure at certain wavelengths. (see reference [1])

## Objectives

**My PhD:** Nanostructure Si cell and understand disorder impact on optical and electrical parameters

**O1:** Low-cost and large surface process
→ Colloidal lithography

**O2:** Understanding the impact of disorder on optical properties of thin silicon films

**O3:** Integrating disordered light trapping strategies in tandem cells

## O1: How to fabricate correlated disorder nanostructures?

### Colloidal lithography process

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**Step 1:** Beads deposition

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SEM image of CL16 sample after beads deposition

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**Step 2:** Deposition of the etch mask
Mask selection depends on etching, here 50 nm titanium for dry etching

**Step 3:** Colloidal removal
Adhesive tape and acetone

**Step 4:** Pattern transfer to substrate
by ICP-RIE etching

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SEM cross-section image of ET-Si-08 after etch mask removal

## O2: How do we characterize disorder?

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**Structure factor**
Describe the arrangement of the structure

$$S(q) = \frac{1}{N} \sum_{m} \sum_{n} \exp\{iq \cdot (r_m - r_n)\}$$

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**Pair correlation function**

$$g(r) = \left\langle \frac{1}{\phi^2} \sum_{m} \sum_{n \neq m} \delta(r_m) \delta(r_n - r) \right\rangle$$

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## Outlook

**NOW**
Colloidal lithography

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* Understanding the importance of the substrate charges

* Fabricating other geometries of etching profile with wet etching (inverted pyramid)

* Exploring more complex pattern (mix of beads sizes)

How does the pattern impact the optical performances?

**Integration on silicon thin-film (≈20 µm)**

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* Validating an increase in absorption

* Comparison of the optical performance of these structures with periodic references and correlated disorder fabricated by polymer blend lithography.

* Understanding the impact of disorder on the optical and electrical performances

How does the pattern impact the global performances of a tandem cell?

**FINAL GOAL**

Integration in tandem solar cell

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* Solar cell integration

* Simulation of patterned tandem cells

## References

[1] Vynck, K., Burresi, M., Riboli, F. et al., Nature Mater 11, 1017-1022 (2012). https://doi.org/10.1038/nmat3442

[2] Massiot, I., Cattoni, A. & Collin, S., Nat Energy 5, 959-972 (2020). https://doi.org/10.1038/s41560-020-00714-4

[3] Terao, T., Nakayama, T., Phys. Rev. E 60, 7157 (1999). https://doi.org/10.1103/PhysRevE.60.7157

## Acknowledgement

The authors acknowledge the support of the French Agence Nationale de la Recherche (ANR), under grant ANR-22-PETA-0005 (PEPR TASE, project IOTA).

This work is also partly supported by LAAS-CNRS micro and nanotechnologies platform, member of the French RENATECH network.

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Laboratoire conventionné avec

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