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Abstract
The highest energy conversion efficiency recorded for a single junction silicon solar cell is 25.0% which is almost 8% higher than efficiencies typically achieved for current commercially-produced silicon wafer-based solar cells. One of the key requirements for producing high efficiency solar cells is fine-scale patterning of dielectric layers. Although laboratory-fabricated cells have typically used photolithography to achieve patterning dimensions less than 10 um, these approaches are too expensive to implement commercially. Consequently, new cost-effective dielectric patterning methods are required if cell efficiencies that approach those achieved in laboratories are to be commercially realised.
This thesis describes a new dielectric patterning method, called direct etching, which has the potential to achieve fine-scale patterning of silicon dioxide and silicon nitride layers at low cost. The method uses a fluid deposition device, such as an inkjet printer or aerosol jet printer, to deposit a source of fluoride ions onto an acidic, water-soluble polymer layer. The hydrofluoric acid etchant is only produced locally where etching is required making the method much safer than existing patterning techniques which use immersion etching.
The inkjet implementation of the direct etching method can be used to etch hole openings of diameter 35-50 um and grooves of width 30-50 um. Initial solar cells were fabricated to demonstrate the ability of the method to reliably etch grid patterns for front metal contacts. The etched grid patterns were successfully metallised using both electroless metal plating and a new light-induced metal plating technique. Furthermore, initial results using an aerosol jet printer suggest that grooves as narrow as 10 um may be etched using this new technique at current commercial wafer processing throughput rates.
A final important attribute of this new method is its low-environmental footprint. In addition to consuming small amounts of readily available chemicals, the method produces small amounts of easily-managed waste. If the expected improvements in patterning resolution can be achieved, then this new dielectric patterning technology has the potential to reduce the large gap that currently exists between the efficiencies of laboratory- and commercially-produced silicon solar cells.