Photovoltaics

Photovoltaics is a key technology within alternative energies. Solar cells enable generation of electricity for a wide range of applications: large scale utilities, commercial and residential roof top installations and various other on-grid and off-grid application. Improving the cell efficiency and reducing the manufacturing cost of solar cells will even increase this broad range of applications.

Reducing the thickness of solar cells offers multiple advantages. The substrate cost for crystalline silicon is still a significant part of the total module costs - reducing the thickness allows reducing the cost. The PV roadmap predicts crystalline silicon wafer thickness of 100µm by 2020. Reducing the wafer thickness increases the risk of wafer breakage during processing, which would require to shut down the processing line to clean out the broken wafer. Temporary bonding and debonding enables breakage-free PV cell production by bonding the thin substrate on a carrier wafer. The carrier wafer provides mechanical stability during the entire manufacturing process. At the end the thin substrate is debonded and mounted into the PV module.

Besides the economical advantage ultra thin solar cells enable a higher cell efficiency. Theoretical calculations taking into account auger- and radiative recombination showed an optimal cell thickness of 40µm (Kerr et al., 29th IEEE PVSC, 2002). Thin PV cells can be either mounted on a rigid or a flexible substrate. Integration into a flexible substrate reduces the weight and opens the field of use for silicon solar cells.
For multi-junction solar cells based on compound semiconductor materials temporary bonding and debonding is used for layer transfer from the growth substrate to the final substrate.

 

 

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Wafer thickness roadmap; CTM Group, PV Roadmap for crystalline silicon, Edition March 2010, http://www.itrpv.net/. Courtesy of Semi PV Group  

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Thin PV cell manufacturing based on temporary bonding and debonding