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Abstract
The challenges of global warming and the need to curb man-made carbon emissions requires us to switch to renewable sources of energy. In order for photovoltaic power to be cost-competitive with coal and receive wide-spread acceptance the cost for solar power must drop to below $1/Watt. The International Technology Roadmap for Photovoltaics has identified two main things that must occur in order for this price bar to be met: commercial solar cells must become more efficient; and the manufacturing costs must be reduced.
The goal of this thesis is to develop a high efficiency, cost-effective solar cell and explores novel patterning and metallization methods in order to achieve this. The Passivated Emitter Rear Contact (PERC) cell, developed at UNSW, is a cell design that has been able to achieve efficiencies over 22% in the laboratory. The key design features that have allowed it to achieve these high efficiencies are selective emitters under the front contacts, and passivated rears with point contacts. This thesis develops new cost-effective method that replicate the design of the PERC cell. In the laboratory the patterning of the cell structures is done using photolithography; here photolithography is replaced with inkjet printing.
Due to the skyrocketing price of silver in recent years, reducing the manufacturing cost of solar cells requires the elimination of silver for the front contacts. There has been some success both in industry and in the lab of using plated Ni and Cu for the front finger contacts. This form of metallization is used in place of silver for the front contacts in this thesis.
An innovative processing sequence is developed by the author that allows the PERC cell structure to be manufactured using inkjet printing and metal plating. This allows us to achieve the goal of realizing high efficiency cell structures using commercial production methods. Three broad types of Ni plating are investigated in this thesis: electroless Ni plating; Ni light-induced plating (LIP); and bias-assisted Ni LIP. Copper plating was mainly performed by LIP, although early experiments also looked at electroless Cu plating.
Cells with pseudo- over 17.5% were successfully fabricated as part of this thesis using the new PERC processing sequence based on inkjet printing and metal plating. One of the major difficulties encountered during this thesis was high series resistance of the plated contacts. This resistance was able to be brought down to below 1.5 cm2 using innovative new plating techniques developed by the author.