Chapter 7
Crystalline Silicon Solar Cells:
Heterojunction Cells
Sylvère Leu and Detlef Sontag
Abstract In contrast to conventional crystalline homojunction cells, heterojunction
cells (HJT cells) work with passivated contacts on both sides. This chapter explains
the functioning of such passivated contacts; it discusses the tunnel effect: an effect,
which is important for these contacts. The role of the various layers within HJT cells
is described. The advantages and disadvantages of the various cell architectures for
HJT cells are explained. Since high-efficiency HJT cells usually consist of n-type
material, the difference between n-type and p-type material is described in more
detail: the term “capture cross-section” is introduced. Capture cross-sections play a
decisive role in the recombination mechanisms studied with the goal of differentiating
n-type and p-type silicon. Thereafter, the fabrication procedures for HJT cells are
discussed; in particular, the advantages of texturing in the crystal plane (100) for
monocrystalline cells. The authors also describe how the depth of microcracks can
be measured with the Bevel method—and how much wafer material has to be etched
off, so as to obtain a surface free of microcracks. The last section shows the favourably
low TC-values of HJT cells.
7.1 Introduction
In Chap. 5 we have already learnt that passivation of the reverse side can be improved
if a permanent electrical back surface field (BSF) is established by suitable process
steps. In the discussion of PERC cells, we also found that aluminium oxide has better
passivation properties than a silicon-aluminium alloy fabricated with an aluminium
paste on the back.
In order to further increase the passivation quality, an additional adaptation of the
cell structure is necessary. Increasing the passivation quality increases both the open
circuit voltage and the fill factor FF and, thus, also the efficiency η of the solar cell.
S. Leu · D. Sontag (B)
Meyer Burger Technology A.G., Gwatt, Switzerland
e-mail: dsontag@web.de
S. Leu
e-mail: sylvere.leu@ciptec.ch
© Springer Nature Switzerland AG 2020
A. Shah (ed.), Solar Cells and Modules, Springer Series in Materials Science 301,
https://doi.org/10.1007/978-3-030-46487-5_7
163
Crystalline Silicon Solar Cells:
Heterojunction Cells
Sylvère Leu and Detlef Sontag
Abstract In contrast to conventional crystalline homojunction cells, heterojunction
cells (HJT cells) work with passivated contacts on both sides. This chapter explains
the functioning of such passivated contacts; it discusses the tunnel effect: an effect,
which is important for these contacts. The role of the various layers within HJT cells
is described. The advantages and disadvantages of the various cell architectures for
HJT cells are explained. Since high-efficiency HJT cells usually consist of n-type
material, the difference between n-type and p-type material is described in more
detail: the term “capture cross-section” is introduced. Capture cross-sections play a
decisive role in the recombination mechanisms studied with the goal of differentiating
n-type and p-type silicon. Thereafter, the fabrication procedures for HJT cells are
discussed; in particular, the advantages of texturing in the crystal plane (100) for
monocrystalline cells. The authors also describe how the depth of microcracks can
be measured with the Bevel method—and how much wafer material has to be etched
off, so as to obtain a surface free of microcracks. The last section shows the favourably
low TC-values of HJT cells.
7.1 Introduction
In Chap. 5 we have already learnt that passivation of the reverse side can be improved
if a permanent electrical back surface field (BSF) is established by suitable process
steps. In the discussion of PERC cells, we also found that aluminium oxide has better
passivation properties than a silicon-aluminium alloy fabricated with an aluminium
paste on the back.
In order to further increase the passivation quality, an additional adaptation of the
cell structure is necessary. Increasing the passivation quality increases both the open
circuit voltage and the fill factor FF and, thus, also the efficiency η of the solar cell.
S. Leu · D. Sontag (B)
Meyer Burger Technology A.G., Gwatt, Switzerland
e-mail: dsontag@web.de
S. Leu
e-mail: sylvere.leu@ciptec.ch
© Springer Nature Switzerland AG 2020
A. Shah (ed.), Solar Cells and Modules, Springer Series in Materials Science 301,
https://doi.org/10.1007/978-3-030-46487-5_7
163