Silicon sandwich

Materials World magazine
1 Jul 2018

As silicon-based solar cells approach their maximum theoretical efficiency, perovskite-silicon double junction cells could be the next standard form for solar cells.

A sandwiched material integrating a perovskite cell directly on top of a silicon solar cell has shown record power generating efficiency at 25.2%. Its cost, ease of manufacture, and compatibility with silicon cell production may help it to become the new standard for solar cells.

A joint team between the École Polytechnique Fédérale de Lausanne (EPFL) and the Centre Suisse d’Electronique, Switzerland, was drawn to increases in efficiency of perovskite cells over the last nine years of research. Authors of the study, Florent Sahli and Jérémie Werner said, ‘By combining the two materials, we can maximise the use of the solar spectrum and increase the amount of power generated. The calculations and work we have done show that a 30% efficiency should be possible.’

Silicon’s surface comprises a series of pyramids measuring around five microns that trap light. 

Combining the two materials requires evaporation methods that form an inorganic base layer that fully covers the pyramids and allows the pervoskite to be deposited in liquid form. This layer is porous, allowing it to retain the liquid before it is heated to crystallise a homogenous film of pervoskites atop the silicon pyramids. 

No added steps

Sahli said, ‘Until now, the standard approach for making a perovskite/silicon tandem cell was to level off the pyramids of the silicon cell, which decreases its optical properties and therefore its performance, before depositing the perovskite cell on top of it. It also added steps to the manufacturing process.’

The techniques used are directly compatible with current industrial monocrystaline silicon-based technologies. Christophe Ballif, head of the EPFL Photovoltaics Laboratory, added, ‘We are proposing using equipment that is already in use, just adding a few specific stages. Manufacturers won’t be adopting to a whole new solar technology, but simply updating the production lines that they are already using for silicon-based cells.