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Double side contacted cells with innovative carrier-selective contacts

Periodic Reporting for period 2 - DISC (Double side contacted cells with innovative carrier-selective contacts)

Reporting period: 2018-04-01 to 2019-09-30

The DISC project addresses the need to reduce the consumption of fossil fuels by developing key technologies for the next generation of high-performance photovoltaic (PV) solar cells and modules. The DISC project approach is to focus on the only way to fully exploit the potential of silicon to its maximum: through the use of so-called passivating contacts or carrier selective contacts and junctions, which allow the carrier to cross without recombination. Such contacts allow for simple device architecture, a reduction of Si wafer thickness, an enhancement of the energy yield, which will be key elements for achieving very low electricity costs.

Objectives – Sustainability
- Apply a life cycle thinking approach to assess the environmental, social and economic impacts and benefits across the entire value chain ==> Provide a platform for long term growth and to enhance the viability and attractiveness of the prototypes
- Extending the life time of the installations through improvements to the reliability and durability of the PV modules ==> Addressing the cost and expertise often needs to fix and maintain PV modules once in place

Objectives – Technological
- Develop prototype double-side contacted Silicon solar cells with carrier selective junctions, targeting efficiencies
o >= 25.5 % on cell area >100cm2 , and
o > 22 % at module level, compatible with low manufacturing costs

Objectives – Scientifically
- Increase knowledge on the different layers and interfaces, in particular on the understanding how the carrier selective junctions operates (CSJ), - and analyse their interaction with transparent conductive oxides (TCOs) and metallization

Objectives – Costs, manufacturing readiness
- Take into account already from the beginning a reduction of the material consumption and the transferability of processes to production equipment at low costs of 0.40 $/Wp on module level with mid-term potential of 0.33 - 0.35 $/Wp
- Targeted high module efficiency will imply lower Levelized Costs of Electricity between 0.04 – 0.07 $/kWh
- Demonstrate pilot manufacturing readiness at a competitive cost by cost assessment of the entire value chain from wafer to module level

Objectives – Market perspective
- Strengthen the PV industry in Europe by
o Help partners ECOSOLIFER and TOTAL (solar cell and PV module producers) to increase efficiency, reliability and durability of their modules and thus help to improve their market position, in particular for inner-European market.
o Improve portfolio of equipment manufactures VON ARDENNE, MEYERBURGER and MECO based on the new technologies developed in DISC for their export-oriented business.
o Results created within DISC also interesting for other solar cells technologies and module makers in Europe, including new actors ==> Repositioning EU at the forefront of PV technology development.
During the first period, the development of single components has been successfully finalized by completing WP1 (CSJ formation) and WP2 (TCO deposition). In addition, the most tasks of the WP3 (metallization) are ending while all technical targets are achieved so far.
The best components of each work packages have been integrated into solar cells within the WP4 (high efficiency solar cells and modules). By involving four different partners in three different countries, solar cell efficiencies up to 21.2% has been achieved, although each component are not optimized yet. The detailed analysis performed in WP6 (characterization and modelling) pointed out that TCO is the limiting component that needs to be improved to achieve higher cell efficiency. This is because the surface passivation quality of poly-Si based CSJ layers suffers significantly during the TCO deposition step, caused by sputter damage.
The consortium has decided to continue the project work with following three routes:
1. Development of TCO deposition techniques with low sputter damage by keeping same cell design. The additional investigation in WP2 showed that the hydrogen in TCO and the post-annealing step at elevated temperature are the key to recover the sputter damage. By applying these knowledges, the cell efficiency could be increased up to 22.2% with indium-free TCO and silver-free metallization on industrial size wafers.
2. Neglecting the TCO layers by direct metallization on the poly-Si based CSJ layers. The metallization is realized with a lithography step. The proof of the concept has been demonstrated with a cell efficiency of 20.8%, but the radiation damage during the metallization step affected Voc and hence final cell performance strongly.
3. Solar cells featuring poly-Si based CSJ only on the rear side has been evaluated and cell efficiencies up to 22.5 % has been achieved. This cell architecture presents excellent transparency resulting in higher current, however the front side, with no CSJ, appears to be the limited components for the Voc.

The module development has been performed separately with a different cell design in combination with single components developed within DISC project. Optimized encapsulation process on Meyer Burger’s smart-wire technology for half-cells enabled the module power of 322W. Accelerated aging test performed at Meyer Burger on module made with SHJ cells from CEA-INES is so far passing more than 3 times IEC standards.
As part of WP5 (Economical assessment, LCA and social acceptance), the life cycle analysis has been performed by comparing the common cell design with industrial standard PERC and HJT solar cells. The LCA shows that DISC cells with 25% cell efficiency has lower CO2 impact than PERC+. In addition, SHJ has the lowest CO2 impact due to its high cell efficiency and bifacial energy gain. The sensitivity analysis regarding cell production in China versus Europe shows that the production in Europe is advantageous across all categories, except for equal performance for freshwater eutrophication and metal depletion.
WP7 (Dissemination and Exploitation) was focused on disseminating the results from other WPs and support it with communication actions, based on project webpage updates, Research Gate updates, newsletter release and institutional e-mail lists. A common exhibition booth at the EUPVSEC 2019 and a common workshop with Nextbase and Ampere are carried out successfully.
Although the target cell efficiency of 25.5 % has not been achieved within the project’s duration, the excellent single components (which ones) developed within the DISC project are also compatible with SHJ technology as recently demonstrated by CEA-INES with 24.4 % SHJ solar cell. Furthermore, the DISC project contributed to strengthening the PV industry in Europe, since the industry partners like Meyer Burger, Von Ardenne and Meco successfully exploited the project outcomes to their equipment or production plant.

DISC has the potential to contribute significantly to direct and indirect job creation in Europe. There is greater potential for job creation in the downstream sector than the upstream sector as downstream activities are more labour intensive. DISC, with its focus on innovation, has the potential to contribute to gross value added (GVA) in the PV industry, as well as other associated technologies, such as manufacturing, energy storage and recycling.

The synergies, bilateral cooperation and results created within DISC will be also interesting for other solar cells technologies and module makers in Europe, including new actors.
DISC-Organization