High efficiency laser doping silicon solar cell with aluminium oxide rear side passivation

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Copyright: Xiao, Bo
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Abstract
Technologies that could further improve commercial silicon solar cell cost effectiveness are explored in this thesis. The screen printed p-type silicon solar cell efficiency is limited by two factors: Al screened rear and defects within p-type silicon bulk. To solve this problem and further improve solar cell performance, AlOx is used as a rear side surface passivation dielectric and hydrogenation processes are tuned to effectively reduce defects within bulk silicon. The first part of the thesis aims to improve the effective lifetime of the silicon wafer by optimising AlOx surface passivation and silicon bulk hydrogenation processes. Laser doping through AlOx/SiNx and metallization to form local contacts are studied. Solar cells are fabricated in the second part of the thesis. AlOx has shown excellent passivation of p-type silicon and suitability for laser doping technology. A high fixed charge density of over 1012 cm-2 and low interface defect density of below 1011 eV-1cm-2 are achieved with ALD AlOx deposited on -OH terminated p-type silicon surfaces. As a result, the surface recombination velocity is controlled at below 8 cm/s. SiNx, as hydrogen source, is added onto AlOx for rear side surface passivation. After hydrogenation under controlled illumination, a significant improvement in silicon bulk lifetime by 500 μs is demonstrated. High iVoc values of 726 mV and 710 mV have been achieved with ALD and PECVD AlOx/ SiNx rear passivated pseudo cell structures. The AlOx passivation dielectric is shown to be an effective dopant source. A peak doping of over 1020 cm-3 is detected by ECV measurement in P+ regions formed by laser doping AlOx. Laser conditions are optimised to reduce damage along the lines caused by Gaussian laser energy distribution across the laser beam. Double side laser doped solar cells with rear AlOx/SiNx passivation are fabricated. The rear reflector is improved, leading to the current density being increased to over 40 mA/cm2 and a solar cell efficiency of above 19% is achieved with the AlOx/SiNx rear passivated solar cell. Further process optimisation by reducing the edge isolation and laser doping damage shows the potential of increasing cell efficiency to over 21%.
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Author(s)
Xiao, Bo
Supervisor(s)
Stuart, Wenham
Alison, Lennon
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Publication Year
2014
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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