PVs constitute one of the main technologies to achieve the targets defined by the EU Energy Roadmap 2050, to reduce the greenhouse emissions to 80-95% below 1990 levels, and increase the share of renewables in the energy production mix to 75%. In addition, thin film PV technologies will be of key importance in the future integration of PV in residential and industrial/commercial buildings (BIPV) as well as in the automotive sector (AIPV). Thin film PV production currently uses two raw materials (In and Ga) which are listed as Critical Raw Materials (CRM) in the European Commission’s Review of the list of critical raw materials for the European Union (COM(2014) 297). Therefore, for the consolidation of independent and secure European PV technology, and to meet our greenhouse and energy supply commitments, it is essential to overcome the PV CRM constraint.

Kesterites are formed from low toxicity metals (Cu, Sn, and Zn) which are abundant in the earth’s crust. This offers a secure supply chain because the production of these metals are not controlled by any one country. Kesterites constitute the most rational and realistic option for PV Industry beyond Si-based technologies, because they have demonstrated very good stability at lab scale. Kesterites also have a realistic potential to achieve the efficiency levels required for transfer of the processes to relevant industrial environments in the short term. Kesterite technology is also fully compatible with current Cu(In,Ga)Se2 (CIGS) production lines, ensuring that European producers of CIGS technologies can easily introduce the kesterite technology.

In this frame, STARCELL targets the optimisation of the material processes and the device interfaces to achieve a challenging solar cell efficiency of 18% (16% for a 10×10 cm2 area mini-module) by the end of the project.

Our project allows the definition and demonstration of a European PV technology covering all innovation aspects, from scientific, to those required in the future production of modules.

STARCELL integrates fundamental studies of materials and devices with the most advanced synthesis and characterization techniques, followed by validation of the technology in a relevant industrial environment, and the definition of the steps to reach the market. In short, the project proposes a multidisciplinary working concept based on 4 pillars with an ambitious but realistic efficiency road-map.

STARCELL aims to substitute two critical raw materials (In and Ga) used in conventional thin film photovoltaic (PV) technologies, via the introduction of sustainable kesterite (Cu2ZnSn(S,Se)4 – CZTSSe) semiconductors.

Eliminate all materials classified as CRM from cost effective thin film PV technologies through development and use of earth abundant kesterite materials from Cu, Zn, Sn, S and Se.

Optimise materials, processes and devices to achieve a kesterite solar cell with 18% efficiency (16% at mini-module level) at a competitive cost at TRL5.

STARCELL builds up on the successful foundations of the knowledge and experience of the project partners, all of them with a high level of credibility and commitment. The consortium has been designed with a very good balance between Academy and Industry, and each partner brings to the project unique and highly necessary expertise skills. Moreover, STARCELL was conceived in a circular economy approximation, and from the beginning the consortium was built with the aim to cover the whole value chain; from the more fundamental aspects relying with basic properties of the materials, to the most applied ones solving problems related to PV devices, and finally considering the key aspects of future Exploitation of the technology.

WP1. CRM-free PV absorber materials
WP1 is divided into 5 tasks to address main absorber challenges through the study and modification of the material’s intrinsic properties, improving the current electrical and transport charge parameters toward values comparable to those reported for CIGS. Task T1.1 is dedicated to the optimization of reactive thermal processes; task T1.2 to the analysis of the impact of order/disorder effects and to propose possible technological solutions; task T1.3 is devoted to the analysis of extrinsic doping of the material; task T1.4 deals with the introduction of graded band-gap concepts; and finally task T1.5 gives support to all the previous tasks with the required advanced characterization methodologies. The main targets of this WP are:

Increase the minority carriers life time to values larger than 20 ns
Reduce the deep defect density below 1015 cm-3
Reduce the Urbach Energy below 20 meV
Increase the minority diffusion length to values larger than 5 µm
WP1 Leader contact details:

Dr. Marcel Placidi (IREC)
e-mail: [email protected]
Tel .: +34 933 56 26 15

WP2. Device re-design
WP2 of STARCELL project is divided into 4 tasks to experimentally address materials and processes innovations related to the different parts of the solar cells structure: T2.1 is dedicated to the back contact, while tasks T2.2 is linked to the buffer layer. T2.3 is related to absorber surface passivation and T2.4 is transversal task dedicated to structural characterization of the different interfaces. The main targets of WP2 are:

Device efficiency ≥18% at cell level with Cd-free buffer layer in small area (≥0.5 cm2)
Demonstration of devices with RS < 0.4 Ω.cm-2 and RSh > 4 kΩ.cm-2
VOC deficit at the same level of CIGS high efficiency devices (< 400 mV)
WP2 Leader contact details:

WP3. Materials and devices simulation
The main objective of WP3 is to perform simulations of materials and devices in order to accelerate characterisation and optimisation of kesterite thin-films and provide novel directions for achieving high-efficiency solar cells. WP3 is divided in 2 main tasks, the first one dealing with the simulation of materials and the second one with the simulation of solar cell devices. Both tasks are divided in sub-tasks. A third task is related to closely-linked supporting experimental characterisation of materials and devices.

WP3 Leader contact details:

WP4. Scale-up, test, validation
To successfully bring kesterite technologies to the commercial level, efficient transfer from academia to industrial partners is required. The transfer from laboratory scale to industrial prototype is usually a time consuming step that mainly consists of process uniformity improvement (both thin-film deposition and thermal treatments) to drastically lower the performance gap between small and industrial-size devices. This step has been challenging for CIGS solar cells and is still subject to intensive research and development with a significant performance level difference between laboratory scale cells and minimodules, in the order of 4 to 5% [1]. WP4 of STARCELL involves 3 main tasks, the combination of which will lead to an efficient kesterite technology up-scale. T4.1 is dedicated to the up-scale of the processes to mini-module size, with the fabrication and optimization of 10×10 cm2 mini-modules and 12.5×12.5 cm2 solar cells. T4.2 is focused on encapsulating and testing solar modules based on devices produced in T4.1 and assessing their viability in real and simulated operating conditions. T4.3 is dedicated to the systematic analysis of the proposed strategies to improve the kesterite absorber from the current baseline knowledge and device quality using the Failure Mode and Effect Analysis (FMEA) method to provide constant feedback and improvement leads to the partners.

With this in mind, the main objectives of WP4 is the transfer of the knowledge developed in WP1 and WP2 for the rational scale-up of the kesterite technology to demonstrate:

Large scale lateral uniformity both, at the material (composition, thickness, <5% deviation) and at the device (spatially resolved PL/EL and thermography analysis, less than 8% in PL/EL/tomography absolute intensity variation) level with careful design of interconnection strategies for mini-modules and medium-size module fabrication.
Demonstration of high degree of durability under real operating conditions: the target is less than 10% efficiency loss after 6 months of operation under real conditions.
10×10 cm2 monolithically integrated mini-modules and 12.5×12.5 cm2 cells based on CZTSSe absorbers with efficiencies up to 16%.
WP4 Leader contact details:

WP5. Recycling/reuse, LCA
In WP5 we will set-up and optimize at the laboratory scale different physical and chemical processes, which will be integrated into an optimized and scalable recycling process. The proposed recycling strategy has been conceived to recover main elements in the kesterite absorbers, and taking into account the cost and scalability of the process.

Besides, A LCA of STARCELL technology will be performed, which will analyse greenhouse gas (GHG) emissions, use of resources (incl. energy, minerals, water and land), and the impacts on human health and on ecosystems. It will be carried out following appropriate methodologies (e.g. CML, IMPACT 2002+), and according to the ISO standards 14040 and 14044, to the Product Environmental Footprint (PEF) Guidelines developed by the EC and the International Life Cycle Data System (ILCD) Handbook (EC JRC-IES 2010). LCA will be carried out in two steps. In a first step (T5.5), the LCA of the reference technology will be performed. At the end of the project, the LCA of the technology developed during the project will be performed (T5.6). The comparison of the environmental impacts of the reference technology with the project’s solution will be conducted to conclude on the fulfilment of the environmental objectives of the project, particularly in relation to the reduction in the use of CRM and the improvement of technology’s sustainability. Then, the overall objective of this WP is to develop, optimize and demonstrate an effective recycling process for STARCELL technology, which will be developed at the laboratory scale. Besides, this WP aims also to quantitatively assess the environmental progress provided by the technological developments conducted during this project. Specific objectives for this WP include:

To develop a laboratory scale process for the recovery of Se from kesterite cells
To evaluate and compare the efficiency of different recycling paths for the recovery of metals in kesterite absorbers (Cu, Zn and Sn). To investigate different potential recycling methods, including electrochemical separation, and extraction with organic solvents.
To define, optimize and validate a recycling process for kesterite cells, considering both scalability and cost aspects. To achieve an efficiency of 75% in the recovery of Se, with a purity higher than 95%.
To provide a LCA of a reference PV technology (most probably CIGS), and of the PV technology developed during the project
To validate that the final STARCELL design reduces the exposure to CRM, and improves the sustainability
WP5 Leader contact details:

WP6. Dissemination and exploitation
The main goal of WP6 is to implement the dissemination, communication and exploitation strategy described in section 2.2, to implement the strategy for raising public awareness about the project throughputs and to promote and manage exploitation of the project results according to the Exploitation and Business Plan of STARCELL. Dissemination, communication and exploitation measures will address the full range of potential users (Stakeholders) including research, commercial, investment, social, environmental, policy making, setting standards, skills and educational training. These activities will be coordinated by the Exploitation & Innovation Board, in collaboration with the Advisory Board.

WP6 Leader contact details:

WP7. Coordination and management
The main objectives of WP7 are:

Management of the administrative and financial aspects of the project;
Coordination and set-up of the organizational structure and decision-making mechanisms of the project;
Management of the communication between the partners, and between the consortium and the EC;
Monitoring, evaluating and documenting the progress of the action.
WP7 Leader contact details: