To ensure that photovoltaics contributes significantly to future world energy production, the cost per watt of producing solar cells needs to be drastically reduced. The use of n-type silicon wafers in conjunction with industrial print technology has the potential to lower the cost per watt of solar cells. The use of n-type silicon is expected to allow the use of cheaper Cz substrates, without a corresponding loss in device efficiency. Printed metallisation is well utilised by the PV industry due to its low cost, yet there are few examples of its application to n-type solar cells. This thesis explores the use of n-type Cz silicon with printed metallisation and diffusion from printed sources in creating industrially applicable solar cell structures. The thesis begins with an overview of existing n-type solar cell structures, previous printed thick film metallisation research and previous research into printed dopant sources. A study of printed thick-film metallisation for n-type solar cells is then presented, which details the fabrication of boron doped p-type emitters followed by a survey of thick film Ag, Al, and Ag/Al inks for making contact to a p-emitter layer. Drawbacks of the various inks include high contact resistance, low metal conductivity or both. A cofire regime for front and rear contacts is established and an optimal emitter selected. A study of printed dopant pastes is presented, with an objective to achieve selective, heavily doped regions under metal contacts without significantly compromising minority carrier lifetime in solar cells. It is found that heavily doped regions are achievable with both boron and phosphorus, but that only phosphorus paste was capable of post-processing lifetime compatible with good efficiencies. The effect of belt furnace processing on n-type silicon wafers is explored, with large losses in implied voltage observed due to contamination of Si wafers from transition metals present in the belt furnace. Due to exposure to chromium in the belt furnace, no significant advantage in using n-type wafers instead of p-type is observed during the belt furnace processing step. Finally, working solar cells with efficiencies up to 16.1% are fabricated utilising knowledge acquired in the earlier chapters. The solar cells are characterised using several new photoluminescence techniques, including photoluminescence with current extraction to measure the quality of metal contacts. The work in this thesis indicates that n-type printed silicon solar cell technology shows potential for good performance at low cost.
| Identifer | oai:union.ndltd.org:ADTP/205198 |
| Date | January 2008 |
| Creators | Edwards, Matthew Bruce, ARC Centre of Excellence in Advanced Silicon Photovoltaics & Photonics, Faculty of Engineering, UNSW |
| Publisher | Publisher:University of New South Wales. ARC Centre of Excellence in Advanced Silicon Photovoltaics & Photonics |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
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