Thermal (Solar) Photovoltaics Using Luminescence Upconversions

Next generation, high-efficiency photovoltaic systems are expected to play a significant role in addressing the global need for renewable energy sources. To be effective, these systems must maximize absorption across the solar spectrum, while minimizing fundamental heat losses. In order to achieve this goal, several new approaches are currently being explored, which predominantly focus on the use of multiple band-gaps. A more universal approach is provided by the conversion of heat into electricity, since this process is suitable to non-solar energy conversion as well. This project will use a luminescence upconversion process to efficiently convert heat into electricity. Phase I performed an experimental and theoretical analysis of the optical properties of several semiconductor materials under relevant operating conditions. The analysis showed that an efficiency in the range of 10-20% could be obtained at operating temperatures of several hundred degrees centigrade, indicating performances comparable or higher than other small-scale, direct heat-to-electricity conversion methods. Phase II will: (1) refine the system model to determine the optical bandgap energy, operating temperature, and bias voltage; design a multible emiter with enhanced extraction efficiency; design and construct a prototype system using a surrogate heat source; and determine the efficiency of the prototype system. Commercial Applications and other Benefits as described by the awardee: The luminescence upconversion approach should provide an added value to existing and future photovoltaic systems, by converting the waste heat generated by those systems. In addition, the approach should provide a higher Carnot efficiency than other available thermal energy converters; as such, it could provide renewable energy in situations where other photovoltaic approaches cannot ¿ e.g. in industrial plant heat exchangers, geothermal sources, and power plants.