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Periodic Reporting for period 3 - PEDAL (Plasmonic Enhancement and Directionality of Emission for Advanced Luminescent Solar Devices)


Applying photovoltaic (PV) panels to buildings is an important application for wider PV deployment and to achieving our 20% Renewable Energy EU targets by 2020. PEDAL will develop a disruptive PV technology where record increases in efficiency are achieved and costs...


Applying photovoltaic (PV) panels to buildings is an important application for wider PV deployment and to achieving our 20% Renewable Energy EU targets by 2020. PEDAL will develop a disruptive PV technology where record increases in efficiency are achieved and costs dramatically reduced;
(1) Diffuse solar radiation will be captured to produce higher efficiencies with concentration ratios over 3 in plasmonically enhanced luminescent solar concentrators (PLSC). Current LSC efficiency achieved is 7.1%, [1]. This proposal will boost efficiency utilising metal nanoparticles (MNP) tuned to luminescent material type in LSCs, to induce plasmonic enhancement of emission (PI and team have achieved 53% emission enhancement). MNP will be aligned to enable directional emission within the LSC (being patented by PI and team). These are both huge steps in the reduction of loss mechanisms within the device and towards major increases in efficiency.
(2) Plasmonically enhanced luminescent downshifting thin-films (PLDS) will be tailored to increase efficiency of solar cells independent of material composition. MNP will be used, where the plasmonic resonance will be tailored to the luminescent species to downshift UV. MNP will be aligned to enable directional emission within the PLDS layer, reducing losses enabling dramatic increases in a layer adaptable to all solar cells.
(3) These novel systems will be designed, up-scaled and a building integrated component fabricated, with the ability not only to generate power but with options for demand side management.
Previous work has been limited by quantum efficiency of luminescent species, with this breakthrough in both the use of MNP for plasmonic emission enhancement and alignment inducing directionality of emission, will lead to efficiencies of both PLSC and PLDS being radically improved. PEDAL is a project based on new phenomena that will allow far reaching technological impacts in solar energy conversion and lighting.

The objectives are:
• To engineer composites (luminescent species (dye/QD) and MNPs in polymer) for PLSC and PLDS and to determine, validate, and maximize manipulation of the optical properties of luminescent species through modifying the localized electrical boundary condition by exploiting the Plasmonic field.
• To achieve record efficiency in a Luminescent Solar Concentrator by exploiting plasmonic coupling phenomena between metal nanoparticles and luminescent species (dye/QD) to enhance emission and alignment of MNP for directional emission.
• To achieve record efficiencies using Luminescent Downshifting Layers to generate more power from a matched solar cell by exploiting plasmonic coupling phenomena, converting solar radiation outside the bandgap of the cell to within its absorption band, along with alignment of MNP to achieve directional emission.
• To develop the first static building integrated PLSC component capable of achieving a concentration factor of 3 or more in diffuse solar radiation.
• To develop the first static building integrated PLDS layer on a commercial PV module capable of achieving an increase in PV efficiency.
• To investigate the balance of systems options for the building integrated devices to enable compatibility with building demand side energy management.

Work performed

Period covered by the report: from 01/04/2015 to 30/09/2016
Periodic report: 1st
1. Overview of the action\'s implementation for this reporting period
The following section outlines the tasks and deliverables that have been completed as outlined in the PEDAL proposal. It provides a (i) global overview of the implementation of PEDAL as well as presenting (ii) the dissemination and training activities by the PI and her team in the Solar Energy Applications Group (SEAG) at Trinity College. Further to this (iii) problems that have arisen have been outlined and the delays explained. These issues have been resolved and the team continues to work hard to achieve the outputs of PEDAL
(i) Overview of PEDAL implementation
Plasmonic Luminescent Down-Shifting (pLDS) and Plasmonic Luminescent Solar Concentrator (pLSC) are new optical approaches to increase PV device efficiency by using plasmonic coupling between luminescent materials and metal nanoparticles (MNP). The optical properties of fluorescent species can exhibit dramatic spectral changes in the presence of metal nanoparticles. It is therefore proposed to achieve record efficiency in pLDS and pLSC layers by exploiting plasmonic coupling phenomenon to enhance absorption/emission and alignment of MNP for directional emission. The optical response of metal nanoparticles and their interaction with luminescent species can be investigated by optical measurement of absorption and emission. The main challenge, however, is controlling the composite structure to achieve maximum enhancement.
The first phase of this research is to prepare stock solutions of MNP, mainly Silver and Gold Nanorods (Ag NRs, Au NRs) to be used in further step with luminescent materials (BASF Lumogen series of dyes, rare earths complex Eu(tta)3phen) and QDs with high LQE).

Synthesis of Ag NRs:
• Preparation of Ag NRs stock solution
Plasmonic coupling with an optical emitter molecule is a function of several parameters and one of them is the surface plasmon resonance (SPR) frequency of the MNPs, which is a function of size and shape. Therefore it is required to synthesize Ag NRs/Au NRs with precise control over shape & size consequently the aspect ratio to investigate & optimize the Plasmonic coupling. The bottom up approach synthesis procedure was used to synthesize Ag NRs. In this process, Hexadecyltrimethyl Bromide (CTAB) was used as a template to facilitate the growth of NRs at room temperature. The procedure was a seed mediated approach and a similar recipe will be used in the future to synthesize Au NRs. Silver ions were reduced with strong reducing agent (sodium borohydride) in the presence of trisodium citrate, as capping agent stabilizer. Then, the prepared seeds were added to a solution containing more metal salts (Na OH), a weak reducing agent (ascorbic acid) and to the CTAB.
• Optimisation of Ag NRs growth solution
Getting a stable and high yield of Ag NRs is crucial as it insures lesser amount of impurities in the solution. Temperature, pH, size of the seeds, impurities are some of the factors that influence the aspect ratio and yield of the NRs. Optimisation of Ag NRs has been achieved through optical measurements and Microscopic measurements. UV-Vis spectrometer was used to measure the absorbance of Ag NRs. Figure 1 shows UV-Vis spectra for Ag NRs prepared in water. The graph in the left shows UV-Vis spectra for Ag NRs grown with 60 µl seed solution and has a longitudinal peak at 700nm but the yield of NRs is quite low as can be seen by the intensity of the longitudinal peak of the NRs. The graph on the right however, shows UV-Vis spectra of Ag NRs after optimisation of the synthesis procedure, with a higher yield of the NRs. The peak at 440 nm in both graph spectra are attributed to the presence of spherical or/and triangles spheres.

The morphology and size distribution of the Ag NRs were characterised by SEM images using ZEISS Ultra PLUS at an accelerating voltage of 5 kV. After the

Final results

During PEDAL, the intrinsic properties of the solar cells will not be modified. Indeed, PEDAL will only allow the development of a new technology that will improve the performance of these solar cells by matching the solar emission with their absorption band. PLSC and PLDS can be considered as photon conversion techniques and are optimized as an independent optical process, dissociated from the particular physical properties of the operating semiconductor material or solar cell architecture. As a result, the photon conversion devices may be combined with all existing solar cells devices. The optical option is much more versatile, allowing independent and unique research; a method of PV system improvement, lowering of thermalisation and easy implementation at industrial level.

This proposal is a completely new approach (based on plasmonics and directional emission in luminescent devices) for solar cell efficiency improvement, which will require long-term and high quality research. Not only is the underlying physical phenomena highly novel and unconventional, but PEDAL also avoids changing the composition of the PV materials, which would be the standard approach to this problem.

The final products of this project will be new, completely portable, adaptable building component (PLSC) or as an efficient plastic matrices (PLDS) that will be suitable for their adaptation onto all types of solar panels.

PEDAL is an ambitious and, at the same time, realistic project, with clear and specific goals both in the scientific and engineering aspects. The solutions suggested by this project will mean not only a radical improvement of solar cell performance, but also an ambitious research at the basic level with a view to industrial applications. The approach of this project represents a great challenge both for the scientific, technological and engineering fields.

In summary, this project will enable highly significant scientific advances in the field of photon energy conversion processes due to its originality, high scientific content and its expected results. Moreover, PEDAL is a project based on new phenomena that will allow very high technological impacts in terms of solar energy conversion. The progress beyond the state of the art are multiple: new knowledge, new advances for Science and new concrete results for plasmonic enhancement of emission in both PLSC and PLDS systems as well as the alignment of MNP enabling directional emission, as well as improved building integrated devices.

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