Self-aligned carrier-selective PEDOT:PSS contacts on optically highly transparent boron-emitters

- Electro-deposition of PEDOT:PSS demonstrated on n- and p-type silicon.
- Electro-deposited film features suitable work-function to contact valence band of silicon.
- Fermi-level at PEDOT:PSS/silicon interface proves to be de-pinned from band middle.
- Boron emitter surface passivated by electro-deposited film.
- Self-aligned deposition on patterned passivation layer of n-type silicon solar cell demonstrated.

As the efficiency of silicon solar cells increases continuously, recombination at the metal contacts becomes more and more limiting, unless the contacts are passivated. Passivating contact layers on the front side, however, usually lead to parasitic absorption. To prevent this we develop a new self-aligned deposition process to implement a passivating layer only under the metal contacts. As passivating layer for the contacts on an optically highly transparent boron emitter we use PEDOT:PSS, which can be electro-polymerized at an anodic surface in an aqueous electrolyte. This electro-deposition technique is used to deposit PEDOT:PSS in the openings of the patterned dielectric passivation layers on the boron emitter of an n-type silicon solar cell. We demonstrate that the electrical properties of the electro-deposited PEDOT:PSS layer are suitable for a passivating contact layer and that the Fermi-level is de-pinned at the interface with silicon.