# Recent advances in Si materials for competitive and sustainable TOPCon and Heterojunction solar cells and modules

Mickael Albaric, Sébastien Dubois, Etienne Pihan, Adrien Danel

► To cite this version:

Mickael Albaric, Sébastien Dubois, Etienne Pihan, Adrien Danel. Recent advances in Si materials for competitive and sustainable TOPCon and Heterojunction solar cells and modules. CSSC 12 - 12th International Workshop on Crystalline Silicon for Solar Cells, May 2024, Hangzhou, China. cea-05506206

HAL Id: cea-05506206

https://cea.hal.science/cea-05506206v1

Submitted on 27 Feb 2026

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# Recent advances in Si materials for competitive and sustainable TOPCon and Heterojunction solar cells and modules

S. Dubois, M. Albaric, S. Harrison, B. Martel, T. Desrues, B. Marie, E. Pihan, S. Rousseau

CSSC12 – Hangzhou (China) - 2024

<figure><img src="image_4.png" /></figure>
# Introduction: the amazing growth of solar

## Historical and mid-scenario forecast for global PV installation (GW)

2023: 413 GW of installed module capacity

**Production capacities are approaching the TW level**

<figure><img src="image_5.png" /></figure>

Source: BloombergNEF. Note: MENA is Middle East and North Africa. Details in BNEF's Capacity tool (web | terminal).

Solar is a key lever in the fight against climate change (CO2 emissions reduction)
# Introduction: new challenges for c-Si PV

## TW scale production (yearly)

- Small gains in efficiency & reliability -> Huge reductions in CO₂ emissions

- Push carrier lifetime towards the intrinsic limit

- Increase the efficiency of single-junction devices

- Development of Si-based tandem

- Understand and mitigate degradation & reliability issues related to the new cell/module technologies

## New challenges related to this TW scale manufacturing

- Improved manufacturing:

- ✓ Higher productivity

- ✓ Cost-effective processes

- ✓ In-line characterization, data processing, ...

- Sustainability-related aspects:

- ✓ Critical materials management

- ✓ LCA analyses, Eco-design

- ✓ Carbon footprint reduction

- ✓ Recycling (Si kerf, End-of-life modules, ...)

Developments at both material and device (cell, module) levels are necessary
<figure><img src="image_6.png" /></figure>

Provide two examples of cross-cutting developments from materials to cells/modules

* New approach for the edge passivation of Si HeteroJunction (SHJ) cut cells

* ✓ *PV performance gains*

* ✓ *High TRL development*

* ✓ *Process ready for industrial transfers*

* Sustainable Perovskite/TOPCon tandem cells from Cast-Mono silicon

* ✓ *PV performance gains & Low-environmental impact*

* ✓ *Low TRL development*

* ✓ *On-going studies*
<figure><img src="image_7.png" /></figure>

Provide two examples of cross-cutting developments from materials to cells/modules

## ☐ New approach for the edge passivation of Si HeteroJunction (SHJ) cut cells

* ✓ PV performance gains

* ✓ High TRL development

* ✓ Process ready for industrial transfers

## ☐ Sustainable Perovskite/TOPCon tandem cells from Cast-Mono silicon

* ✓ PV performance gains & Low-environmental impact

* ✓ Low TRL development

* ✓ On-going studies

<figure><img src="image_8.png" /></figure>
# Edge passivation: context, motivation

High effective carrier lifetime required for high efficiency cells -> **surfaces perfectly passivated**

HETEROJUNCTION

<figure><img src="image_9.png" /></figure>

TOPCon

<figure><img src="image_10.png" /></figure>

## The paradox of the PV industry!

* Larger formats of wafers: M10, G12, ...

* Half cells and shingle for advanced module architectures

► « Large » cells have to be cut!

### Shingle-modules

* High perimeter/surface ratio

* Non passivated edges

► Efficiency losses

~1%<sub>abs.</sub> for SHJ shingle!

Edge passivation processes have to be
developed for SHJ and TOPCon cells
# Edge passivation: context, motivation

## Conventional cells cutting approach

* Laser scribe & mechanical cleavage

<figure><img src="image_11.png" /></figure>

Edge cannot be passivated

## Thermomechanical cleavage

* Laser-induced thermal stress to cleave the cell

<figure><img src="image_12.png" /></figure>

Edge compliant with passivation processes
# Edge passivation: CEA approach

## Innovative cutting process

* Modification of the ingot squaring step

Crystallographic cleavage
in the wrong direction

<figure><img src="image_13.png" /></figure>

<figure><img src="image_14.png" /><figcaption>Conventional Cz
ingot squaring</figcaption></figure>

<figure><img src="image_15.png" /><figcaption>Top view</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>Alternative Cz
ingot squaring</figcaption></figure>

<figure><img src="image_17.png" /></figure>

* Purely mechanical crystallographic cleavage (no heating)

* Minimum cell degradation → no laser used

* Compatible with all cell technologies (SHJ which are sensitive to T increase)

Short diamond tip scribe at the edge,
followed by an homogeneous bending
pressure to propagate a crack

<figure><img src="image_18.png" /><figcaption>SHJ shingle cells</figcaption></figure>

<figure><img src="image_19.png" /></figure>
# Edge passivation: CEA approach

Are the 45°-oriented wafers compliant with production lines?

<figure><img src="image_20.png" /><figcaption>Tests on CEA
SHJ pilot line</figcaption></figure>

<figure><img src="image_21.png" /><figcaption>Tests on KalyonPV
PERC production
line</figcaption></figure>

<figure><img src="image_22.png" /></figure>

<figure><img src="image_23.png" /></figure>

No significant influence on efficiency and breakage rate
# Edge passivation: CEA approach

## Focus on the edge morphology

<figure><img src="image_24.png" /></figure>

* No structural defects

* Edge compliant with surface passivation steps

But... SHJ cells do not withstand T above 250°C

Development of specific passivation processes were needed

## Combination of AlOx (ALD) & Light-Soaking

<figure><img src="image_25.png" /></figure>

B. Martel et al, SolMat (2023)

<figure><img src="image_26.png" /></figure>

AlOx -> conformal deposition

Cost-effective & high throughput process

Up to 80% efficiency losses recovery
# Edge passivation: CEA approach

## Advanced investigations

B. Martel et al, SolMat (2023)

<figure><img src="image_27.png" /></figure>

Interfacial layer that would improve the chemical passivation

Edge passivation assessed by complementary techniques (e.g., PL, LBIC)

<figure><img src="image_28.png" /></figure>
# Edge passivation: CEA approach

## Integration into SHJ shingle modules -> Efficiency gain preserved

S. Harrison et al, SiliconPV (2024)

## But reliability issues due to parasitic AlOx on metal grid!

<figure><img src="image_29.png" /></figure>

<figure><img src="image_30.png" /></figure>

<figure><img src="image_31.png" /></figure>

Specific protocols developed to avoid AlOx deposition on the interconnected areas -> **Reliability preserved**

**Overall procedure ready for industrial transfers**

<figure><img src="image_32.png" /></figure>

<figure><img src="image_33.png" /></figure>
<figure><img src="image_34.png" /></figure>

Provide two examples of cross-cutting developments from materials to cells/modules

☐ New approach for the edge passivation of Si HeteroJunction (SHJ) cut cells

✓ *PV performance gains*

✓ *High TRL development*

✓ *Process ready for industrial transfers*

☐ Sustainable Perovskite/TOPCon tandem cells from Cast-Mono silicon

✓ *PV performance gains & Low-environmental impact*

✓ *Low TRL development*

✓ *On-going studies*

<figure><img src="image_35.png" /></figure>
# PK/Si tandem cells: context

* Si single-junction cells feature performances approaching the theoretical limit (29.4%)

* 2T Perovskite (PK) on Silicon (Si) tandem cells -> efficiency values higher than 35% achievable via cost effective approaches

<figure><img src="image_36.png" /></figure>

## Record devices:

* From FZ or Cz wafers

* Recombination junction usually based on In-rich layers

* « Low-T processed » bottom cell -> limitations in the selection of the HTL material and related deposition processes

* Complex fabrication process

**Goal:** development of an alternative approach for sustainable PK/Si tandem solar cells
# PK/Si tandem cells: alternative approach

## Double side poly-Si/SiOₓ passivated contacts (TOPCon²) bottom cell

<figure><img src="image_37.png" /></figure>

<figure><img src="image_38.png" /></figure>

<figure><img src="image_39.png" /></figure>
# PK/Si tandem cells: alternative approach

## TOPCon² bottom cell fabrication process

T. Desrues et al, 48th IEEE PVSC (2021).

### LPCVD route

- Surface preparation

- SiOₓ-Poly-Si (i) LPCVD

- Ph ex situ doping (implant)

- B ex situ doping (implant)

- Co-annealing

- Rear TCO

<figure><img src="image_40.png" /></figure>

- Ultra-simplified fabrication process

- Ultra-thin poly-Si layers limiting optical losses while providing high surface passivation (700+ mV)

## 3x3 cm² Tandem solar cells with 25% efficiency (FZ Silicon, CMP surfaces)
# PK/Si tandem cells: Cast-Mono as alternative?

<figure><img src="image_41.png" /><figcaption>« Subgrain-free » lab-scale n-type Cast-Mono ingot</figcaption></figure>

* ✓ **Strong gettering effect** developed by thin n- & p-type **poly-Si** layers

* ✓ n-type poly-Si gettering equivalent to the conventional phosphorus diffusion gettering

T. Desrues et al, in AIP Conference Proceedings (2022).

« Subgrain-free » Cast Mono wafers compliant with high efficiency PK/Si tandem cells!
# PK/Si tandem cells: Cast-Mono as alternative?

## First integration of Cast-Mono TOPCon² BC in PK/Si tandem

Solvant-based process for the PK Top Cell processing

➤ CMP required

<figure><img src="image_42.png" /></figure>

- Striations observed only for Cast-Mono

- Could be related to SiC or SiN inclusions within the materials

Top Cell process non-optimized for « thin » (PV) wafers (cell cutting & current matching issues)

<figure><img src="image_43.png" /></figure>

CEA PK Top-Cell baseline: record @ 28.4% (9 cm² FZ CMP wafers)

<figure><img src="image_44.png" /></figure>

<table><thead><tr><td>Material</td><td>Efficiency (%)</td></tr></thead><tbody><tr><td>Cz</td><td>21.7</td></tr><tr><td>Cast-Mono</td><td>21.5</td></tr></tbody></table>

- Low η differences bw Cz & Cast-Mono

- Paths for η improvements identified
# Conclusion

Silicon cells production capacity at the TW level:

* Even small gains in efficiency & reliability matter

* Sustainable technologies have to be developed

Developments at both material and device (cell, module) levels are necessary

Two examples of cross-cutting developments from materials to cells/modules

* ☐ New approach for cell cutting and edge passivation, validated at module level

* ☐ First PK/Si tandem cells prepared from Cast-Mono wafers
<figure><img src="image_45.png" /></figure>

Thank you

Acknowledgment to European Union through the funded projects IBC4EU (Grant Agreement no. 101084259

Acknowledgment to Clean Energy Transition Partnership through the funded projects EPOBOC.