Next-generation interdigitated back-contacted silicon heterojunction solar cells and modules by design and process innovations

Periodic Reporting for period 2 - NextBase (Next-generation interdigitated back-contacted silicon heterojunction solar cells and modules by design and process innovations)

Okres sprawozdawczy: 2018-04-01 do 2019-09-30

It is generally accepted that PV will play a major role in the renewable energy mix which needs to take the globe to zero net CO2 emission by 2050. Current PV mainstream technology is based on crystalline silicon solar cells and research and development in this field are mainly oriented towards the improvement of the energy conversion efficiency and the reduction of module production costs. However, despite record solar cell efficiency, the IBC approach is seldom considered as an option for mainstream c-Si technology due to the high production costs. The NextBase project aimed to demonstrate that IBC-SHJ solar cells and modules with higher efficiencies are competitive with the existing PV devices. The 4 main objectives and the obtained results of NextBase project are listed below:
1) Demonstrate IBC-SHJ solar cells with efficiency > 26.0%
Up to 25.4 % efficiencies were demonstrated on 25 cm2 FZ wafers and 92 cm2 industrial Cz wafers. These results are the European record to date for such solar cell technology.
2) Demonstrate IBC-SHJ solar modules with efficiency > 22.0%
A certified 1-cell laminate with 23.82% efficiency (97.2% CTM), a 22% efficient mini-module, and a 60 cell proof-of-concept module are demonstrated.
3) Develop an industrial prototype PECVD reactor for IBC-SHJ solar cells
An industrial prototype PECVD reactor for IBC-SHJ solar cells is developed at MBR with a whole process to manufacture tunnel IBC SHJ solar cells.
4) Develop processes that allow IBC-SHJ solar module cost of <0.35 euro per watt peak (€/Wp)
The CoO for SHJ-IBC modules is projected to be 0.275 €/Wpk. The SHJ-IBC concept only needs an increase of 0.5% absolute cell efficiency to be competitive with standard SHJ solar modules.

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/Ohm.cm
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
Processing of IBC-SHJ devices with efficiency > 26.0 %
Tool related tasks:
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
Characterization and modeling related tasks:
Numerical device simulation and optimization
Reliability assessment and failure modes analysis
Performance and energy yield assessment with light soaking and outdoor measurements
Cost and life cycle analysis related tasks:
Technology scale-up impact analysis: cost scenario for IBC-SHJ production plant (500 MWp)
1.2.2 Main results and their exploitation and dissemination
Demonstrated 25.4 % champion efficiency of IBC-SHJ on a cell level and a 24.2% on a full area wafer at the R&D stage.
Demonstrated a 22% efficient mini-module and assembled a 60-cell proof-of-concept module
Development of a lean industrial process for > 25 % efficiency tunnel IBC-SHJ device
A full 60-cell bifacial IBC-SHJ module using the SmartWire Contacting Technology
A dedicated characterization tools for IBC-SHJ using Raman based optical profilometry and large-area photoluminescence (PL) imaging.
A competitive Cost of ownership for IBC-SHJ module

The NextBase project has achieved progress beyond the state of the art. A summary is given below:
Advanced silicon wafer preparation is achieved using a novel Multi Ingot-Pulling technique.
Novel layers and contact materials enabling the fabrication of a 26%-efficient IBC were demonstrated.
The leanest process flow is developed for > 25 % efficiency IBC-SHJ devices.
IBC-SHJ process integration for mass production
The developed small area lab scale process is successfully transferred to a large-area prototype tool with high efficiencies up to 25.4%.
Module encapsulation and interconnection of IBC-SHJ devices
The NextBase project demonstrated a full 60-cell bifacial IBC-SHJ module using SmartWire Contacting Technology.
1.3.2 Expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)
The main topics that are advanced by NextBase are listed:
Definition of an industrial technological route for IBC-SHJ
NextBase identified challenges and limitations of various approaches for thin-film material, patterning, light management, interconnection and encapsulation, on which basis a most cost-competitive industrial route for high-efficiency IBC-SHJ cells and module production was defined.
Significantly increased mass production potential of IBC-SHJ
With the demonstration of a prototype PECVD reactor capable of producing high-efficiency IBC-SHJ solar cells on industrial wafer size and suitable interconnection technology for IBC-SHJ modules, the TRL of the IBC-SHJ technology was increased to a level, where the PV community becomes aware of the unfolded potential of IBC-SHJ technology to become a next generation PV mainstream.
Reducing life-cycle environmental impact
NextBase provides a thorough LCA analysis of SHJ-IBC technology. The results here show that the process flow developed by NextBase has a very low impact.
Contributing to solving the global climate and energy challenges
NextBase projected an LCOE ranging between 36-60 Euros/MWh for IBC-SHJ PV systems in Europe.
Nurturing the development of the industrial capacity
The NextBase project provides support to NC in defining wafer specification and testing wafer quality, which was essential for NC to make the market driven transition from p-type to high quality multi-pulling n-type ingot growth. MBR gained know-how from the NextBase consortium to pursue the realization of the PECVD reactor prototyping and to overcome process technological boundaries.
Contributing to the strengthening the European industrial technology base
A successful demonstration of the objectives within this project can open the door for a European industry for high efficiency solar cells and modules at all the value chain (up to new installation approaches) and can fill the gap of high efficiency modules for rooftop applications. NextBase will permit maintaining further the European leadership position of PV tool manufacturer by offering a new generation of high technology tool and processes.
Decreasing operation and maintenance costs, hence creating new business opportunities
The project demonstrated that relatively low CoO could be achieved despite the process additional complexity of IBC-SHJ architecture.

Overall NextBase approach

Periodic Reporting for period 2 - NextBase (Next-generation interdigitated back-contacted silicon heterojunction solar cells and modules by design and process innovations)

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