As the environmental costs associated with fossil and nuclear fuels become more apparent, the case for clean energy sources, such as solar cells, becomes increasingly strong. The major problem with solar cells is the efficiency with which the light is converted into electrical energy and the fabrication costs. This research project directly addresses these problems by applying recent and revolutionary developments in silicon bipolar technology to the fabrication of silicon solar cells.
The results showed large reductions in series resistance of solar cells with polysilicon emitter technology contacts. The researchers demonstrated that a fluorine implant had a double effect on the performance of the cells: it reduced the series resistance and improved the passivation of the surface of the cell. Overall, an efficiency of 15.3% was achieved by using a back polysilicon contact.
The particular development of interest is the polysilicon emitter, which has led to a factor of more than five in circuit speed over the last ten years. The application of this technology to silicon solar cells should lead to significant improvements in efficiency. Preliminary calculations suggest improvements in the efficiency of state of the art solar cells. There is also no way of improving low recombination emitter design which would lead to large improvements. The concept underlying the low recombination polysilicon emitter is the minimization of all components of
recombination. In a state of the art polysilicon emitter two recombination terms generally dominate, namely recombination in the single crystal emitter and recombination at the polysilicon-silicon interface. The first term is minimized by using novel fabrication techniques to decrease the doping concentration in the single crystal emitter, thereby reducing Auger recombination. The second term is minimized by passivating the interface states using a technique recently developed at Southampton University. The application of this technique to bipolar transistors has led to world record gain transistors.
Funding SchemeCSC - Cost-sharing contracts
SO17 1BJ Southampton
SO9 5NH Southampton