Lifetime and efficiency improvement of organic luminescent solar concentrators for photovoltaic applications
Chapters 4, 5, 6 and 7 are not available in this version of the thesis
In order to achieve the goal of zero net-energy consumption in residential and commercial buildings, substantial research has been devoted to developing methods for energy harvesting from window glass that is capable of passing visible light through the windows of buildings while converting the unwanted invisible solar radiation into electricity. Research has focussed on two particular aspects, namely (i) the integration of thin-film technology for solar radiation transmission control and (ii) light guiding structures for solar radiation routing towards the edges of the glass window.
Recently, photovoltaic (PV) solar cells have been investigated and promoted as products for converting solar energy into electricity. Due to the increased demand for renewable energy sources, the manufacture of PV panels’ arrays has advanced considerably. However, they cannot compete with fossil fuel or nuclear energy, due to the high cost of inorganic solar cells and their low power conversion efficiency (PCE).
To lower the cost per installed capacity ($/Watt) and to use the complete solar spectrum, new PV technologies have been developed, such as solar concentrators. Among the many kinds of concentrators, luminescent solar concentrators (LSCs) have significant industry application potential. Materials used in LSCs are inexpensive, the solar cell size is reduced and no tracking of the sun is required.
In an LSC, the incident sunlight is absorbed by luminescent species, such as fluorescent dyes, quantum dots or rare-earth ion embedded in the active layer (organic or inorganic), which re-emits light in random directions usually at longer wavelengths. In an ideal LSC, all the re-emitted light can be routed towards the edges, where the attached small-area solar cells harvest the light and convert it into electricity.
In this thesis, several contributions are made toward the development of organic LSCs. The first contribution is related to the design and development of multilayer thin film structures containing dielectric and metal layers, using physical vapour deposition, for the control of thermal and solar radiation propagated through glass windows. Measured transmittance spectra for the developed thin-film structures are in excellent agreement with simulation results. For the second contribution, a cost-effective, long-life-time organic LSC device with UV epoxy as a waveguide layer doped by two organic materials is developed. A PCE as high as 5.3% and a device lifetime exceeding 1.0×105 hrs are experimentally achieved.
The third contribution of the thesis is the development of a general method for encapsulating organic LSCs, based on employing three optically transparent layers, (i) an encapsulating epoxy layer and (ii) two insulating SiO2 layers that prevent the dye dissolving into the epoxy layer. The encapsulated organic LSCs demonstrate an ultra-long lifetime of ~ 3.0×104 hrs and 60% transparency when operated in an ambient environment, of around 5 times longer than that of organic LSCs without encapsulation.
Finally, the last contribution of the thesis is the development of a new LSC architecture that mitigates the reabsorption loss typically encountered in LSCs. Experimental results demonstrate significant reduction in photon reabsorption, leading to a 21% increase in PCE, in comparison with conventional LSCs.