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Advanced Thin-Film Technologies for Cost Effective Photovoltaics

Final Report Summary - ATHLET (Advanced Thin-Film Technologies for Cost Effective Photovoltaics)

The main objective of the ATHLET project was to accelerate the decrease of the cost versus efficiency ratio in the use of thin film photovoltaic modules. Such modules have a great potential for cost effective production in the technology of scale; however the relevant alternatives are not yet sufficiently developed.

ATHLET focused on technologies based on amorphous, microcrystalline and polycrystalline silicon as well as on I-III-VI2-chalcopyrite compound semiconductors. The project target unit cost was 0.50 euro/Wp. The value chain was examined in order to improve efficiencies and scale-up existing technology. Lab scale cells with higher efficiencies were demonstrated and module aspects relevant to all thin film solar cells were investigated. The analysis and modelling of materials, processes and devices was an important project component. Sustainability assessments of the proposed solutions were elaborated, to facilitate conclusions on successful implementation strategies of the developed technologies.

ATHLET had numerous scientific and technological objectives, among which the most important were:
1. to improve front and back contacts and the related deposition methods so as to achieve long-term stability, conductivity and transparency;
2. to optimise semiconductors, interfaces and specific buffers aiming at stable and highly efficient solar cells;
3. to optimise encapsulation materials as well as processes based on glass and flexible non-glass materials;
4. to develop high band gap alloys and explore cost-effective tandem devices;
5. to scale-up novel, economically viable processes;
6. to set up a virtual laboratory for device analysis and solar cells modelling, develop analytical methods for materials and devices and produce modelling tools for performance optimisation;
7. to identify machinery requirements for production and focus on improvement of yield, quality and cost of such machinery;
8. to identify and solve performance related problems arising from both the rigid glass and the flexible substrates;
9. to identify suitable in-line compatible patterning methods for super modules and substrate modules as well as to develop alternative monolithic series interconnection methods;
10. to identify potentials for the reduction of energy consumption, material usage and waste and to develop improvement strategies;
11. to assess social benefits and risks from large-scale technology implementation and to elaborate strategies towards an increase of sustainable energy production and
12. to provide training and promote mobility of students and young scientists.

The project activities were structured in six different, interconnected subprojects (SPs), namely:
1. high efficiency solar cells, which focused on increasing the efficiency of the project technologies in comparison to the currently applied alternatives. One of the main issues addressed by this SP was the impact of light trapping. Solar cells were examined for low, intermediate and high growth temperatures.
2. thin film module technology, which examined modular aspects, such as isolated substrates, contact technologies, encapsulation, serial interconnection and demonstration. Experiments on mechanical terminal contacting were performed, in order to select the most viable options for practical use and two innovative methods were developed.
3. chalcopyrite specific heterojunctions, which aimed to optimise large area modules in terms of materials and efficiency. Alternatives were evaluated for probable application in production lines; however several limitations and uncertainties impeded the direct application of the developed solutions at the end of the project.
4. thin film silicon large area modules on glass, which developed suitable machinery for large area modules. The substrate costs proved to be an important limiting factor in the overall cost reduction; nevertheless the SP concluded that the target value of approximately 0.50 euro/Wp was feasible in the medium term.
5. device analysis and modelling, which developed optical, electrical and structural analysis techniques so as to thoroughly understand the cells properties and to develop a data base for the project. The SP led to an increased insight into the solar cells physics, to the understanding of the performance limits of the present technologies and to the development of strategies for cells improvement. The modelling work was available to the other SPs in order to help them characterise and improve the developed cells throughout the project.
6. sustainability, training and mobility, which supported the other SPs by monitoring the environmental and social impact of the proposed technology and focused on the training and mobility of the involved scientists. An environmental screening tool was developed, which also addressed health and safety issues and facilitated options evaluation. Environmental impact analyses were carried out for fully developed production processes and a methodology was developed for considering this impact during the research stage. In addition, the factors influencing market share of thin film technologies were investigated in order to provide an insight into strategic decisions in thin film manufacturing.

The advantages of thin film approaches for photovoltaic modules proved to be related both with cost and reduced environmental impact, as a result of lower material requirements and lower cost manufacturing processes than for the crystalline silicon approach. ATHLET developed alternative solutions which turned out being both environmental friendly and commercially viable, thus accelerating further research towards future large scale applications of the thin film technology in the photovoltaic field.

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