Novel Laser Doping Technology for Silicon Solar Cells

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Copyright: Chan, Catherine
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Abstract
The use of laser doping in the solar cell industry has recently led to the commercialisation of several high efficiency solar cell structures which were historically too costly to produce in an industrial setting. Used in conjunction with industrial-grade silicon wafers, commercial cells with selective emitters and rear surface passivation schemes are now approaching or exceeding 20% efficiency, offering a competitive edge over conventional screen-printed cells with a homogeneous front emitter and a full aluminium rear back surface field. In this thesis, the use of laser doping is proposed as a means to fabricate more complex solar cell structures such as interdigitated back contact (IBC) solar cells or cells with a rear surface floating junction. Both of these structures have been difficult to commercialise due to the need for several masking steps and high temperature diffusions and oxidations which are both costly and not compatible with new low-cost silicon material emerging onto the market. Specifically the use of laser doping to form a contact to an underlying region through a diffused layer of the opposite polarity to the laser doping is investigated. The method is found to be able to be performed without introducing significant recombination, and also to be able to electrically isolate regions of the device or structure on either side of the laser doping from each other. The technique is applied to the edge isolation of solar cells and is found to provide superior edge passivation to a standard cleaving method of edge isolation. The method is applied to form p-type interdigitated back contact (IBC) solar cells with full emitter coverage and only one furnace diffusion step. Advanced bulk passivation techniques are considered and developed for such structures which traditionally require high-quality float zone silicon substrates with long minority carrier diffusion lengths. Whilst the proof-of-concept IBC cell structures fabricated on commercial Czochralski-grown material yielded only a modest efficiency of 14.6%, modelling suggests that the efficiency potential of such a simple structure exceeds 22%. Further work is required to improve the robustness of the fabrication process and suggestions for efficiency improvements in the future are presented.
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Author(s)
Chan, Catherine
Supervisor(s)
Wenham, Stuart
Abbott, Malcolm
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Publication Year
2014
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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