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CHROMTISOL Report Summary

Project ID: 638857
Funded under: H2020-EU.1.1.

Periodic Reporting for period 2 - CHROMTISOL (Towards New Generation of Solid-State Photovoltaic Cell: Harvesting Nanotubular Titania and Hybrid Chromophores)

Reporting period: 2016-09-01 to 2018-02-28

Summary of the context and overall objectives of the project

The issue being addressed is the lack of solar cell technology fulfilling stringent criteria of efficiency, stability, low prize, flexibility, transparency, tunable cell size, esthetics.
This project therefore develops a new solar cell concept and it therefore it falls in the field of photovoltaics.

The society needs such research and concepts (technologies) to boost the solar-to-electricity conversion efficiency and to power so far unpowerable devices and objects.
The CHROMTISOL solar cell concept bears a large potential to outperform existing thin film photovoltaic technologies and concepts due to unique combination of materials and their complementary properties.

Main Objectives of the CHROMTISOL project include:
• Introduction of new type of solar cell with fast and loss-reduced photo-generated carrier

The research focus is given to a new physical concept of a solar cell that explores extremely promising materials, yet unseen and unexplored in a joint device, whose combination may solve traditional solar cells drawbacks (carrier recombination, narrow light absorption). It features a high surface area interface (higher than any other known PVs concept) based on ordered anodic TiO2 nanotube arrays, homogenously infilled with nanolayers of high absorption coefficient crystalline chalcogenide or organic chromophores using different techniques, yet unexplored for this purpose. After addition of supporting constituents, a solid-state solar cell with an extremely large incident area for the solar light absorption and optimized electron pathways will be created.

• Development of advanced techniques for infilling of high-aspect ratio nanotubular TiO2 arrays with inorganic and organic chromophores

The filling method of the first choice (for CIGS, CdS, ZnO and ITO layers inside nanotube arrays) is the Atomic Layer Deposition (further noted as ALD).
However, there are at least 3 other methods to be researched and employed in the project (electrodeposition, solution processing, in-situ synthesis).

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

Workpackage 1: Development and Synthesis of TiO2 Nanotube layers
Development of nanotube layers suitable for their employment in the proposed solar cells concept was carried out already. In particular, uniform nanotube layers with different aspect ratios were realized using new anodization protocols allowing to tailor tube diameters, lengths, wall. We have also understanding how crystalline structures (obtained by various treatments) influences the nanotube properties. The developed nanotube layer are used in WP3.
In the remaining time, we plan to scale up of the nanotube production by synthesis of developed anodic TiO2 nanotube arrays on rigid titanium as well as flexible substrates (PET foils or similar) of different sizes, dimensions and formats.

Workpackage 2: Development of Chromophores
Development of chromophores suitable for the purpose of the deemed solar cell concept was carried out. Two classes of materials were developed - inorganic crystalline semiconductors and organic push-pull sensitizers. They have shown sufficient light absorption capability, optimized HOMO-LUMO fit with TiO2, good anchorage to TiO2 and reasonable stability. Chromophores are chemically and thermally compatible with other constituent creating deemed solar cell. The as-synthesized chromophores are used in WP3.

Workpackage 3: Nanotube Infilling Routes
Deposition of a range of chromophores developed in WP2 inside the TiO2 nanotubes synthesized in WP1 was carried out. For that a broad range of deposition techniques has been employed including Atomic Layer Deposition (ALD), electrochemical deposition, spin-coating and direct in-situ synthesis. For the purpose of homogenous nanotube coating/ infilling, especially ALD was used to a great extent for the first time. During these efforts, some specific challenges connected with the filling efforts had to be overcome. However, due to significant drive of the whole team and efforts spent on this topic, we are ready to proceed to infill inside the nanotubes all necessary parts of the futue solar cells – topic of WP4.

Workpackage 4: Creation of the Solar Cell
Samples produced in WP 3 will receive remaining elements to function as the solar cell. Solar cells prepared in the laboratory will be tested on the photovoltaic performance by photocurrent measurements and solar cell simulator. Strong feedback on the materials development (WP1-2) and filling routes (WP3) is expected that will influence optimization of all components towards solar cells with highest conversion efficiency and stability possible.

For the first three WPs, numerous publications in highly ranked international peer-reviewed journals were published - see the relevant section of this report, please.
Many other are in the preparation. The whole team will for remaining 2 years of the project focus on the realization of the solar cells, i.e. mainly WP4.

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)

Progress beyone state of art:

1) We have shown such a perfect degree of TiO2 nanotube modification than anyone before.This is beacuse
we can perfectly deposit virtually any material inside the nanotubes and significanly alter the properties of the nanotubes.

The ALD tool (purchased partially from the ERC funds and installed at the hosting institution) is a key instrument for it. See attached photograph.
But itself it would not be enough. The team had to built significant skills and develop unique know-how, how to use the technique for the purpose of the project.
This was very succesfull and we plan to utilize / develop it even more and stronger.

It is not just ordinary ALD tool, because it has been equipped with special functionalities to allow deposition
into a high aspect ratio materials, such as nanotube layers in this work. The whole CHROMTISOL team very benefits from this tool,
as it allows really well to coat nanotubes with secondary materials (see illustrative image attached), towards the new solar cells concept.
Noone else in the world has managed and shown, what we did.
The combination of know how on nananotubes and now also ALD seem key for succescull realization of this project.

The results published so far attracted significant attention. This is beacuse we are pushing the limits in the deposition of chalcogenide and other materials to highly porous matrices.
Based on the number of papers, presentations given at conferences (and invitations to conference especially in recent times),
one can state that we became world leaders in the deposition of various materials into high aspect ratio nanostructures.
This knowledge is liked and we are increasingly asked to participate to take a leading role in some complementary activities to this ERC project.

2) We have published new findings on the growth of nanotube layers and aided by modern characterization techniques, we showed for the first time aspects and features not know before.
E.g. we have shown the relationship between the microstructure of the substrates and the nanotube growth.

Expected results
We undertake all steps to realize fully functional solid-state solar cell according to the propose design until the end of the project.
This will be the main result. We will disseminate it via publications, eventually patent application (still not decided) and conference participations.

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