CORDIS - EU research results

Towards Solution-Processable Near-IR and IR Reflective Coatings and Mirrors for Improved Heat and Light management

Final Report Summary - SPIRCAM (Towards Solution-Processable Near-IR and IR Reflective Coatings and Mirrors for Improved Heat and Light management)

Project Summary:
In recent years, rising energy costs have driven the strong need for the development of novel materials systems that promote energy conservation and reduce unnecessary emissions in the building and construction sector as well as in the automotive area. For instance, for both cars and trains, growing concerns about, e.g. pronounced urban heat-island effects; have drastically accelerated the demand for intelligent solar heat management solutions. Since heat is most often a direct consequence of infrared radiation incident on an object, with the heat-producing region being between 750 – 1200 nm, one obvious strategy to reduce heat – and thus the need for excessive air conditioning – is the deployment of IR high reflecting coatings. As a practical requirement, these coatings must retain high transparency over the visible wavelength regime and, ideally, not interfere with the operation of electronic devices.

The coatings and mirrors developed in this project, based on novel organic-inorganic hybrid materials, are an industrially-relevant solution; the project delivered versatile, low-cost and easy-to-process systems that provide various advantages of current state-of-the-art technologies. These coatings and mirrors, which consist of novel organic-inorganic hybrid materials, were aimed at improving heat and light management due to their excellent near-IR (NIR)/IR reflectivity, high transparency in the UV-Visible wavelength regime, and their tunable index of refraction (n).

To achieve this aim, following objectives were set:
1. To develop and characterize the properties of novel hybrid materials, which consist of organic-inorganic blends, with the purpose of providing improved heat and light management for existing and next-generation commercial products
2. To develop multi-layer hybrid material-based photonic structures to be used for NIR/IR operation.
3. To investigate the active control of the optical response for novel photonic structures consisting of electrochromic layers between the developed NIR filters.
4. To incorporate the developed hybrid materials and photonic structures into next-generation plastic electronic devices for improved heat and light management

I set out to meet these project objectives through a well-planned research methodology and approach, and I fully delivered by performing the following research activities: (a) development of hybrid polymer:inorganic hybrids, (b) incorporation of photonic structures in polymer:metal oxide hybrid films, (c) investigation of the active control of the optical response in switchable photonic structures, and (d) incorporation of the hybrid materials into plastic electronic devices for improved heat and light management.

Results of Research Activities and Conclusions

Development of hybrid polymer:inorganic hybrids. Hybrid materials consisting of polymer poly(vinylpyrrolidone) PVP and ZnO, a inorganic transition metal oxide, were developed. Developing a blend of ZnO and PVP is advantageous for plastic electronic and photonic device application, such as improving light management in plastic electronic devices or heat management in commercial buildings.

The optical properties of coatings consisting of the ZnO:PVP hybrids were characterized up to the NIR. It was found that the hybrids showed high optical transmission from 300 to 1400 nm when dried in air or not anneal, while annealing of the blends produced films with the highest optical reflection in the same wavelength range. In addition, the optical transmission can be further enhanced via optimization of the PVP concentration in the blend. In addition to the optical properties of the blend, a structural characterization of the films was conducted via optical and scanning electron micrographs.

Incorporation of photonic structures in polymer:metal oxide hybrid films via micro-moulding techniques. A simple, yet novel approach for introducing photonic structures into our hybrid films was developed. By utilizing solution micro-molding techniques, photonic structures were imprinted onto the surface of the hybrid film. The nano-structured surface, based on either a regular periodic structure or a randomized corrugated structure, could scatter and diffract light of various wavelengths. The films were characterized via scanning electron micrographs and absorption spectroscopy. It was demonstrated that the novel ZnO:PVP hybrid films could be customized with a number of photonic nano-patterns (e.g. lines, triangle gratings, small features (pillars, holes and lines with diverse features, periods). The features that have been successfully imprinted onto our ZnO:PVP hybrid films vary in size and shape, demonstrating the versatility of the process. By altering the surface structure of the hybrid through the developed imprinting process, it is possible to tune the diffraction wavelength to meet the requirements of any optoelectronic device.

Investigated the active control of the optical response in switchable photonic structures. By introducing electrochromic polymers on the developed hybrid materials, active control of the optical response could be demonstrated. The first demonstration of this approach was developed in our laboratories using commercially available electrochromic polymers and ionic liquids. To expand our approach to a solid-state system, bi-layer structures consisting of imprinted ZnO:PVP hybrid films and electrochromic polymers were solution processed with the help of our collaborators. This work is still on going, but will lead to impactful results in very near future.

Incorporation of hybrid materials into plastic electronic devices for improved heat and light management. The ZnO:PVP hybrid films imprinted with photonic structures were incorporated into plastic electric devices, such as polymer solar cells and organic light-emitting diodes. Baseline devices using ZnO-PVP as an interlayer in inverted polymer solar cells were prepared. In first attempts to imprint the hybrids, we found that larger polymer concentrations were required for an effective imprint. Careful optimization of the mechanical and semiconducting properties of the blends is still ongoing, in an attempt to maximize efficiency while ensure good light management.

Potential Impact and Use

The results of this work will be submitted for publication in high-impact functional materials and photonics-related journals. The development of these hybrids for heat and light management is novel, and will lead to exciting exploration into the development of new solution processed coatings and mirrors for NIR activity. In addition, the processing protocols established in this work are entirely adaptable to a large-scale manufacturing process. As such, the work is industrially relevant and competes well with existing technology, and I expect the coatings and photonic structures developed in this work to be easily incorporated into different technologies and products, such as windows for home and commercial buildings.