Silicon solar cells with Low Environmental footprint and Advanced interfaces

Project Information

SiLEAN

Grant agreement ID: 101147275

DOI

10.3030/101147275

EC signature date 23 April 2024

Start date 1 May 2024

End date 30 April 2027

Funded under

• Climate, Energy and Mobility

Total cost

€ 3 379 462,50

EU contribution

€ 3 379 462,50

Coordinated by

FORSCHUNGSZENTRUM JULICH GMBH
Germany

Periodic Reporting for period 1 - SiLEAN (Silicon solar cells with Low Environmental footprint and Advanced interfaces)

Reporting period: 2024-05-01 to 2025-10-31

Summary of the context and overall objectives of the project

Project context: SiLEAN project aims at developing a lean process chain for the next generation of SHJ solar cells with a smaller environmental footprint using: 1) epitaxially-grown wafers with lower energy demand, developing; 2) alternatives to the highly absorptive hydrogenated amorphous silicon (a-Si:H) for the passivation and carrier-selective contact, developing; 3) indium-free contact layers, as well as silver-free metallization concepts, and applying a bismuth-free interconnection.
Technical Objectives:
1) Development of epitaxially grown ultra-thin epi-Si wafers from the gas phase with increased quality and advanced light management.
2) Development of novel passivation concepts
3) Demonstration of novel contacts for thin SHJ solar cells with a strong reduction of scarce materials
4) Validation of SiLEAN solution and integration into mini modules, with high potential for high mass production.
5) Assessment and demonstration of reduced environmental impact
Pathway to impact: This new type of solar cell should achieve higher efficiency (>25.5%), lower manufacturing costs (50% cost reduction of Si wafers and 50% cost reduction for both metallization and TCO), and lower environmental impact (up to 75% lower carbon footprint from epitaxial wafers, no or very low amounts of scarce materials thanks to the developed In-, Ag-, and Bi-free solar cell technology), as compared to nowadays available c-Si solar cells. The SiLEAN technology will offer a viable solution enabling TW-scale production.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Most technical WPs have been active during the first reporting period. Main activities performed and achievements have been:
• WP2-Light trapping in ultra-thin wafers: EpiWafer production was successfully optimized, achieving 90 µm ±10 µm thickness and effective measured minority carrier lifetimes >3.5 ms. Initial light-management strategies, including nano-pyramid texturing and black silicon, demonstrated integrated reflectance near 10% for nano-pyramids and as low as 2.7% on MST, with scalability preparations underway.
• WP3-Novel passivation concepts for ultra-thin SHJ solar cells: For TPC structures, an implied Voc of ~740 mV could be achieved in symmetrical TPC samples. The highest Voc in a full cell structure so far is ~720 mV on Cz wafers. For TMO structures, the highest Jsc of 40.88 mA/cm² is achieved in 4-inch-compatible tool.
• WP4-Developments of novel contacts for ultra-thin SHJ solar cells: For In-free solar cells, a new transparent conductive oxide based on SnOx is showing very promising conductance similar to that of Al-doped zinc oxide but with higher transparency and stability in air. For Ag-free cells, a first reduction in Ag contents is demonstrated with a mixed Cu/Ag paste, showing excellent module reliability. For carbon-based contacts, the first generation of low-temperature screen-printing-dedicated pastes with graphene is now available for testing.
• WP6 -Demonstration of reduced environmental impact: Calculation of improve energy yield has been completed and the evaluation of safety of supply and LCA activties are ongoing

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

A preliminary analysis of market interest and technology overview has been reported in D7.3-Exploitable Results and exploitation routes. We report here the main parts
The PV manufacturing sector is the first target for SiLEAN innovations. Within this ecosystem, three sub-sectors are particularly relevant: wafer production, cell manufacturing, and module assembly.
In wafer production, NexWafe (NXW) leads the development of EpiWafers — ultra-thin, kerf-less wafers grown via gas-phase epitaxy. These wafers offer up to 75% lower carbon footprint and 50% cost reduction compared to traditional Cz wafers. Their use case is clear: replacing Cz wafers in high-efficiency SHJ cell lines, especially where sustainability and material efficiency are strategic priorities. SiLEAN’s material-efficient architecture offers a pathway to local manufacturing independence and cost-effective deployment, making it a strategic fit for regions aiming to scale solar sustainably.
In cell manufacturing, partners like TUD, FZJ, and IMEC are developing SHJ cells using copper-based metallization, TMO passivation, and indium-free TCOs. These cells are ideal for premium product lines and sustainable manufacturing, as described previously. IMEC’s TWILL interconnection technology and GET’s graphene-based inks further support low-cost, low-impact cell designs. These innovations can be scaled through pilot integration with existing SHJ lines, followed by licensing and industrial partnerships.
Module assembly benefits from simplified interconnection and lamination processes. 3SUN, as a leading European module manufacturer, is best placed to integrate SiLEAN technologies into its production lines. The TWILL approach enables low-stress, Bi-free multiwire interconnection, reducing material usage and streamlining module fabrication. Modules based on SiLEAN technology, with their reduced use of silver, indium, and bismuth, can meet these criteria and gain preferential access
Short-term actions include demonstrating compatibility with industrial tools and securing IP protection. Mid-term actions include engaging equipment suppliers for process certification and leveraging EU funding (e.g. IPCEI, Horizon Europe) for infrastructure build-out. On the long-term, the goal is to position SiLEAN technologies as the standard for sustainable SHJ production.