Ion Implantation

Ion implantation is an alternative technique that can be used to dope silicon solar cells. Ion implantation typically consists of [1]:

  1. An ion source, this is to produce the desired ions.
  2. An accelerator, this accelerates the ions to a high energy.
  3. A target substrate, this is the material to be implanted by the ions.

Figure 1: Ion Implantation Diagram

The depth of penetration of the ions is determined by the energy of the ions, ion species and the composition of the target. The process causes damage to the crystal structure; thus, ion implantation is typically followed by an annealing step.

Advantages

The advantages of ion implantation include [1], [3]:

  • Dopant profiles with high precision can be formed.
  • Uniformity and repeatability are more consistent.
  • Single sided doping can be performed,
    • This removes the need for a phosphosilicate glass (PSG) removal and edge isolation.
    • It is also useful for interdigitated back contact (IBC) cells.
  • Both Boron and Phosphorus doping can be performed, hence can be used for n-type or p-type wafers
  • Doping can be performed in patterns, which is ideal for IBC and PERC cell architectures.

Disadvantages

The disadvantages of ion implantation include [1], [3]:

  • Causes damage to the target structure, hence requires an annealing step post-implantation.
    • This is more complex for Boron implantation, which does not lead to an amorphization of the surface region, like phosphorus does.
  • High capital cost

A short animation of ion implantation is shown below.

[1]          Wikipedia. (2018). Ion implantation.

[2]          H. Hieslmair, Latchford, I., Mandrell, L., Chun, M. and Adibi, B, “Ion implantation for silicon solar cells,” Photovoltaics International Volume 182010.

[3]          H. J. O. Jan Krügener, Fabian Kiefer, Felix Haase, Robby Peibst, “Ion implantation for photovoltaic applications: Review and outlook for n-type silicon solar cells,” IEEE, Hannover (2016).