External Quantum Efficiency Measurements and Outdoor Characterisation for PV Luminescent Downshifting Devices

摘要

As part of the European Union energy and climate goals, 20% of the final energy consumption should come from renewable technology, and by 2030 the target has been set to 27%. Harvesting solar energy has the potential to reduce carbon emissions and to provide clean energy contributing to sustainable development. The solar spectrum received at the Earth surface covers a wide range of wavelengths from 290 nm to 3790 nm. In an ideal situation, the absorption spectrum of PV materials should perfectly match the entire solar spectrum in order to convert the maximum photons from solar radiation to electricity. However, there is a large mismatch between the solar emission spectrum and the absorption properties of the present PV materials. At short wavelengths, each photon has a large energy, and therefore the ratio of photons to power is reduced. Any energy in excess of the band gap energy of the solar cell materials is not utilised by the solar cell and instead goes to heating the solar cell and is therefore wasted. Loss mechanisms in photovoltaic represent a practical limit to the solar cell efficiency, and the potential remains to make a better use of the short wavelength radiation. In order for high efficiencies to be achieved in PV technologies, energy loss mechanisms must be reduced. Luminescent downshifting (LDS) layer is a method which aim to convert nonabsorbable solar radiation in the UV (290-400 nm) into absorbable incoming radiation in the visible (400-700 nm) via florescence phenomena, hence increasing the solar optical response for short wavelength radiation. It has been proposed in the late 1970s when Hovel et al. realised that instead of concentrating sunlight high-energy photons could be converted to low energy to overcome the poor solar cell performance in UV, blue light. It involves a luminescent species that is applied in a transparent polymer/glass host material on top of the PV cell.