Novel Approaches for Improving the Performance of Multicrystalline Solar Cells

This project has two main research areas both of which relate to improving the performance of multicrystalline solar cells. The first involves the development of a new technique to texture the surface of multicrystalline silicon material such that capture of light by the cells will be improved. Such textured material is often referred to as "black silicon". There is currently a problem in the solar industry with texturing multicrystalline silicon and in particular material that has been diamond wire sawn. Current methods are either very slow (eg plasma etching) or do not give the required degree of "blackness". Importantly the process which will be researched in this project is performed in the gas phase allowing batch processing of many wafers. This means the technique has more potential as a commercially viable process compared to competing techniques such as plasma etching which require wafer by wafer processing which makes them time consuming. Proof of principal experiments, already performed, indicate the method will work on commercial diamond wire sawn material and so this project will move on to the next stage of the research which will entail optimising the etching parameters in terms of speed to produce an etched surface and the light captured by this surface as a function of wavelength and angle. The investigation will then proceed to determine how the material can be doped using POCl to produce an effective emitter. Techniques to be used include optical measurements, carrier lifetime measurements and EBIC imaging to correlate the spatial characteristics of the emitter junction formed with its electrical performance.

The second part of the project will entail the development of a high temperature gettering process to remove unwanted impurities from the silicon wafers before processing to produce a solar cell. Currently the highest temperature at which gettering processes will work is around 900C but at these temperatures not all impurity precipitates dissolve and diffusion is often slow such that, in the time available, the gettering process is not totally effective. The new process which will be investigated may allow processing at temperatures up to 1150C and so has the potential to be more efficient. In addition at these high temperatures it is expected that etching of the wafer surface will occur that will increase the light absorbed into the material when processed into a cell. Thus, this material will also be studied using some of the techniques used in the first part of the project to determine light capture, and the electrical performance of emitter junctions made in the material. The efficiency of the gettering process will be evaluated using carrier lifetime measurement techniques.

The project is in collaboration with the UK company Tetreon Technologies Ltd who will be involved in developing and supplying the equipment needed to texture silicon surfaces and who have already supplied the furnace required to form emitter junctions using a POCl diffusion process. Tetreon supplies production equipment to the solar industry worldwide and it has been agreed that the student on the project will spend three or more months at Tetreon facilities either in the UK or overseas.

The Themes are:
Energy
Physical sciences