In order to increase the efficiency of industrially produced silicon solar cells and to close the gap between cell efficiencies in laboratory and mass production, new production processes are necessary. Record efficiencies of more than 24% have been achieved for lab-type silicon solar cells. However, this laboratory process includes several additionally process steps like photolithography which is not economical for an industrial application.
The average efficiency for industrially produced mono-crystalline front junction silicon solar cells is in the range of 16-18%.
But now the world-renowned Fraunhofer Institute for Solar Energy Systems (ISE) has introduced a process which they claim can be transferred to industry and has the potential to significantly increase cell efficiencies using Aerosol Jet printing equipment developed by Optomec.
ISE's most recent results were presented on October 1, 2008 at the Crystal Clear "Workshop on Metallization for Crystalline Silicon Solar Cells" held in Ultrecht, The Netherlands.
The Aerosol Jet printed solar cells achieved efficiencies of over 20% when combined with Light Induced Plating (LIP) and Annealing, versus an average efficiency for screen-printed mono-crystalline front junction silicon solar cells in the range of 16-18%.
The narrower, higher integrity collector lines produced by Aerosol Jet deposition systems have higher conductivity and a lower shadowing effect, thereby increasing cell efficiency. In addition, because the process is non-contact, Optomec's Aerosol Jet system can print on thinner wafers and with less breakage than screen-printing.
The Fraunhofer study states "So far, the front side metallization holds the main potential for a further increase in cell efficiency. The main targets are the reduction of the metallized area to reduce shading losses, a low contact resistivity to a lowly doped emitter, and a high line conductivity to transport the current as loss-free as possible out of the cell."
"The cells fabricated in this work combine the advantages of a new advanced front side metallization with an already established rear contact process, which are both industrially feasible. The front side grid was aerosol jet printed and light induced plated achieving line widths below 45 micron. On solar cells with an 110V/sq emitter record cell efficiencies of 20.3% were measured and independently confirmed by Callab ISE."
"In fact in recent work, Fraunhofer ISE has found that the optical width of an aerosol jet printed and plated contact embedded in a module is only 43% of its geometrical width further reducing fill factor and providing increased cell/module efficiencies."
For volume production applications, Optomec has developed a high throughput 40-nozzle Aerosol Jet deposition head that prints a solar cell every 2.5 to 3 seconds. Additionally, the non-contact nature of the Aerosol Jet system enables high yield printing on thinner photovoltaic wafers.
Optomec is the world-leading provider of additive manufacturing systems for high-performance applications in the Electronics, Biomedical, and Aerospace & Defense markets. These systems utilize Optomec's proprietary Aerosol Jet technology and LENS powder-metal fabrication technology. The company has a global customer base of industry-leading manufacturers
For more attend Printed Electronics Europe 2009.
Top image: Optomec's 40 nozzle M3D Aerosol Jet head for volume production.
Reference: Optomec, Fraunhofer Institute