The highest efficiency ever has been reported for Laser Doped Selective Emitter (LDSE) solar cells manufactured in a commercial environment, using commercial grade wafers. It is being presented in a paper by the University of New South Wales (UNSW) and Sunrise Global. Written for the 25th European Photovolatic Solar Energy conference and exhibition in Valencia, the paper boasts an LDSE cell efficiency of 19% on industrial grade 156mm 1Ω.cm p-type silicon wafers. This has been achieved with a corresponding batch average efficiency of 18.6%. The higher efficiency increases the average 30 MW line capacity by 10%. The paper discusses critical aspects associated with the LDSE device and process optimisation.

 

The benefits of a selective emitter have been well established for many years. The LDSE solar cell technology developed at UNSW and patented by NewSouth Innovations (NSi) has shown to achieve quite significant performance and cost improvements over Screen-Printed (SP) Solar Cell. This is due to lower metal shading losses, a better blue response and lower cost of production.

 

Laser doping produces heavily doped regions beneath the metal contacts within an overall shallow emitter. This is an effective and simple way of achieving a selective emitter. The technique allows patterning of the dielectric and laser induced diffusion to occur in a single step. The added benefit that there is no damage to the wafer, which only subjects the wafer to localised heating.

 

SP metal lines are typically 120 microns or greater. The LDSE cells fabricated at Sunrise Global achieved plated metal lines with widths as low as 30 microns, and current density as high as 37.9mA/cm2. Laser doping in LDSE cells can form grooves down to 10 um wide and when plated forms metal lines as narrow as 20microns wide, which potentially achieves a current density as high as 39 mA/cm2.

 

The LDSE cells were fabricated at Sunrise Global on a screen-printed line in an industrial environment, with the exceptions of the two end processes:

1) laser doping and

2) metallisation via plating to replace front silver contact.

 

Most of the surface damage normally caused by laser doping is avoided by careful selection of the laser and its operating parameters. The laser is suitable for mass-production due to the high scan speed. A novel rapid contactless light induced plating (LIP) method, patented by NSi, was used to self-align the nickel and copper metal deposition. Off-the-shelf commercially available LIP equipment is suitable for the plating step.

 

The fabrication steps for the LDSE process can be retrofitted into any standard screen-printed line. By substituting the front Ag printing and putting the LDSE tools between the firing furnace and tester/sorter. Kuei-Chang Hsu, CEO at Sunrise Global Solar Energy says "Sunrise Global will incorporate the LDSE tools in the lines for the next major expansion, once the required tools have been further optimised."

 

NewSouth Innovations Pty Limited (NSi) is a company wholly owned and established by UNSW to commercialise its research and provide technology transfer services by managing agreements on licensing, sale and collaborative partnerships for technologies developed at UNSW. The quality of UNSW’s research provides NSi with an unparalleled advantage in the transfer of technologies to the market place. For more information, visit www.nsinnovations.com.au

 

Sunrise designs, manufactures and markets high-performance solar cells worldwide for residential, commercial and utility-scale power plant customers. Sunrise high-efficiency solar cells generate significantly more power than conventional solar technologies. For more information, visit www.SunriseGlobalSolar.com

 

The School of Photovoltaic and Renewable Energy Engineering is internationally recognised for its research in the area of photovoltaics, most of which is now conducted under the ARC Centre of Excellence in Advanced Silicon Photovoltaics and Photonics. It was also the first organisation in the world to offer undergraduate training in the area of Photovoltaics and Solar Energy, and has since extended the educational programs it offers to include postgraduate and research training opportunities.

 

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