Luminescent Lanthanide Layers for Enhanced Photovoltaic Performance (LEAP)

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.

DIRECT BENEFICIARIES Commercial Private sector: An ambitious, recently-established PV manufacturer, Topcell Solar International (TSI) have expressed in participating in this project as detailed in their letter of support. TSI will directly benefit from the LEAP-frog technology proposed - a new design of solar cells that improve efficiencies of their c-Si and mc-Si solar cells. Thin film a-Si:H and nc-Si:H PV devices will be developed in house and the up-conversion (UC) and down-conversion (DC) layers integrated to their design, indicating a further potential commercial route given a successful project outcome. Other than PV manufacturers, the other industry will be direct beneficiaries of this research are manufacturers of lanthanides materials, glasses and phosphors. If any of the devices, systems or processes that we develop in conjunction with our industrial partner can be shown to outperform conventional methods in new generations of PV modules then the company can expect significant commercial success. Training of Personnel: The PV industry currently reports that the shortage of suitably experienced graduates and post-graduates is a key difficulty facing the industry. This project will support around 11 PhDs and 5 PDRAs and the training and development we have planned will provide personnel fit to work in the PV industry. They will have a knowledge of photovoltaics and specific detailed knowledge gathered from their own research. Policy-makers, UK, China, regional, and devolved governments, and government agencies: As experts in photovoltaics, the academics in this consortium have the opportunity to share detailed knowledge of PV and its role in low-carbon society, sometimes this general knowledge is valuable and often specific outputs of our research provides valuable information that can influence decision making. Our membership has often been asked to advise national and region governments and agencies, this will remain our responsibility. INDIRECT BENEFICIARIES The economic performance of China and the UK, global economic performance, the wider public: The economic performance of the UK and China will benefit directly as described above. However, in the broader sense the UK, Chinese and global economies, and quality of life will benefit greatly or at least be maintained from decreases in the cost of solar energy and the resultant decrease in the reliance on fossil fuels and extent of global warming. Successful outcome of this proposal will have a greater impact on wider economics and to the society in both countries via the development of low cost and high efficiency development of PV systems. In addition, wider acceptance of solar technology in rural parts will directly benefit to the society by reducing environmental pollutions. Reduce PV module costs will also benefit the UK, where financial and energy payback times for such systems are longer than in some other countries due to the cloudier maritime climate.