Luminescent Lanthanide Layers for Enhanced Photovoltaic Performance (LEAP)

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It is now widely accepted that the world's increasing reliance on fossil fuels over recent centuries is causing drastic changes in the Earth's climate. Renewable energy technologies - such as solar, wind and wave energy - offer a pathway for the generation of clean energy. This project concerns photovoltaic (PV) technology - the conversion of sunlight to electricity - and, in particular, involves the application of luminescent materials to PV modules. Shipments of PV modules have been increasing at a steady rate of >40% per annum since 1994 and continued strong growth of 20-30% predicted for the next few years. However, efficiency and price are still the main barriers to reducing the cost of solar electricity.This project seeks to develop a new class of PV devices and modules, based on todays semiconducting technology however utilising luminescent materials to alter the wavelengths contained in the sunlight before the photons interact with the solar cell. Via two techniques known as down-conversion (DC) and up-conversion (UC), we are able to greatly address two of the main loss mechanisms that limit the theoretical performance of a single junction solar cell to about 30%. With DC, we are able to use luminescent materials to absorb photons in the range of 300-500nm (UV through to blue-green light) and for each of these emit TWO photons at about 1000nm, where silicon solar cells respond very efficiently. Preliminary modelling has indicated that such a DC layer applied to the front of a silicon solar cell could increase its absolute energy conversion efficiency (sunlight to electricity) from 16% for a typical production device to 19%. Thus, a huge step change in performance is possible! UC layers are able to collect near-infrared (NIR) light that passes straight through the silicon, and for each of these NIR photons we can emit a single higher-energy photon that can be harvested by the silicon solar cell. The performance of UC layers depends on the intensity of sunlight though, and hence we will design and test these systems under 500-times concentrated sunlight.This project brings together spectral conversion and PV expertise from Heriot-Watt University (HWU) in the UK and matches this with luminescent materials expertise from the Fujian Institute of Research on the Structure of Matter (FJIRSM), one of the Chinese Academy of Sciences (CAS), with the goal of establishing a new class of PV devices that are able to promise a step-change in performance for both c-Si and thin film (e.g. a-Si:H) PV technologies.