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NextBase Report Summary

Project ID: 727523
Funded under: H2020-EU.3.3.2.

Periodic Reporting for period 1 - NextBase (Next-generation interdigitated back-contacted silicon heterojunction solar cells and modules by design and process innovations)

Reporting period: 2016-10-01 to 2018-03-31

Summary of the context and overall objectives of the project

Among the different types of renewable energies, photovoltaics (PV) is considered as one of the most mature technologies. Current PV technology is based on crystalline silicon (c-Si) solar cells and research and development in this field is mainly oriented towards improvement of the energy conversion efficiency and the reduction of module production costs. The NextBase project aims to demonstrate that IBC-SHJ solar cells and modules with higher efficiencies than existing high-efficiency PV devices can be produced at competitive costs. In summary, the NextBase project will realize the following 4 concrete objectives linked to the development of IBC-SHJ devices:
Demonstrate IBC-SHJ solar cells with efficiency > 26.0%.
Demonstrate IBC-SHJ solar modules with efficiency > 22.0%.
Develop an industrial prototype plasma-enhanced chemical vapor deposition (PECVD) reactor for IBC-SHJ solar cells.
Develop processes that allow IBC-SHJ solar module cost of <0.35 euro per watt peak (€/Wp).

The expected outcome of this project is to realize IBC-SHJ solar cells with efficiency above 26.0% and corresponding solar modules with efficiency above 22.0%. Hence, the NextBase project is aiming to lay the foundations for a new PV system value chain in Europe based on innovative next-generation c-Si technology.

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

As planned, we have been working on the following tasks from the beginning to the end of the period:
Wafer related tasks:
Production of low-cost Si wafers with lifetime over resistivity ratio > 2 ms/
Evaluation of thermal processes impact on Si wafer characteristics (finished)
Si wafers chemical texturing for double- or single-side textures
Development of advanced modulated wafer surface texture
Film related tasks:
Advanced a-Si:H and μc-Si:H based materials and TCO/metal stacks
Development and optimization of novel TMOs for selective contacts
Novel FSF and passivation materials for the front side of IBC-SHJ devices
Development of plating for IBC-SHJ devices
Cell process tasks:
Investigation of various patterning schemes
Investigation of light management (finished)
Processing of IBC-SHJ devices with efficiency > 26.0 %
Tool related tasks:
Development of a tool featuring built-in patterning method (finished)
Tooling and SHJ cell fabrication (finished)
IBC-SHJ pilot cell fabrication
Module related tasks:
New generation of interconnection technologies for IBC-SHJ devices
Light management at module level by novel ARCs
Liquid encapsulation process
Characterization and modeling related tasks:
Assessment of loss mechanisms in IBC-SHJ devices (finished)
Investigation of the patterned fingers shapes & their link to the device parameters (finished)
Numerical device simulation and optimization
Development of dedicated IBC-SHJ cell efficiency measurement (finished)
Reliability assessment and failure modes analysis
Cost and life cycle analysis related tasks:
Cost Assessment of the technology (finished)
Technology scale-up impact analysis: cost scenario for IBC-SHJ production plant (500 MWp)

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)

Advanced silicon wafer preparation
In order to reach Voc > 740 mV and Jsc > 42 mA/cm2 the following is done: (i) the production of mono-c-Si ingots through a low-cost multi-pulling process with various resistances and wafer thicknesses, targeting lifetime > 3 ms and oxygen content < 15 ppma; (ii) systematic evaluation and monitoring of thermal treatments to further improve n-type wafer characteristics; (iii) the texturing of either front side or both front and rear side of the wafer for finding the best compromise between optical potential, fabrication process and passivation properties; (iv) the deployment of modulated surface texture at the front side of the wafer for achieving broad-band light in-coupling and light scattering while keeping the flat back side.
Novel layers and contact materials
The reduced size of both electron and hole contacts in IBC-SHJ solar cells can become a critical issue, determining FF and performance limitations due to increased transport losses. A major task of NextBase is the development and assessment of suitable contact stacks, for optimized transport and contact passivation.
High-efficiency IBC-SHJ devices processing
One of the main issues preventing a wider spread of the IBC-SHJ devices to date is their delicate and lengthy processing. A major task is therefore to develop a cost-effective patterning scheme for the rear side of IBC-SHJ devices compatible with the mass production of 6-in devices. Special effort will be dedicated to gain deeper insights into the patterned features characteristics (shape, thickness, surface coverage) that govern the final device efficiency. Moreover, the light management at device level will be optimized, aiming to fully exploit the available sunlight. This will eventually allow the fabrication of IBC-SHJ devices with efficiency > 26.0% on full 6-in wafers, which is well beyond the current state-of-the-art for such devices, both in terms of efficiency and device area.
IBC-SHJ process integration for mass production
A new generation of plasma tool featuring built-in masks option is needed to validate the concept of silicon layer patterning with a potential of high throughput. This project is dedicated to designing the tool, its tooling and the manufacturing of large area IBC-SHJ solar cells. The tool design is oriented to be able to provide high quality, uniform a-Si:H or c-Si:H doped layers on 4 to 6 wafers per carrier with a throughput between 10-20 wafers per hour.

Expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)
The NextBase objectives are to develop industrially relevant technologies enabling for the production of competitive high performance silicon wafer based solar cells and modules, yielding solar cells based on IBC-SHJ architecture with efficiency above 26% and corresponding solar modules with efficiency above 22%.

Significantly increased technology performance
Combining the IBC and SHJ concepts that ensures high Jsc due to omitted front metal contact and high Voc thanks to the excellent surface passivation by amorphous silicon with beyond state-of-the-art low resistivity electron and hole collecting film stacks and additional improvement of wafer quality, light management and transparent front layer stacks.

Reducing life-cycle environmental impact
NextBase developments will be conducted at technological steps with full LCA to ensure that a positive environmental impact is achieved with the developed technologies. Environmental impact studies will be realised at device level and prospected at the production level by industrial partners (500 MWp scenario).

Reducing renewable energy technologies installation time and cost and/or operational costs, hence easing the development of renewable energy sources within the energy mix
Increasing the efficiency of PV cells and modules by application of low temperature processes resulting in reduced module costs of < 0.35 €/Wp. Detaile

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