The perovskite
film (black, 200-300 nm) is covered by Spiro.OMeTAD,
Graphene with gold
contact at one edge, a glass substrate and
an
amorphous/crystalline silicon solar cell. Credit: F. Lang / HZB
(October 2, 2015) HZB
team develops elegant process for coating fragile perovskite layers with
graphene for the first time. Subsequent measurements show that the graphene
layer is an ideal front contact in several respects.
Silicon absorbers primarily convert the red portion of the
solar spectrum very effectively into electrical energy, whereas the blue
portions are partially lost as heat. To reduce this loss, the silicon cell can
be combined with an additional solar cell that primarily converts the blue
portions. Teams at HZB have already acquired extensive experience with these
kinds of tandem cells. A particularly effective complement to conventional
silicon is the hybrid material called perovskite. It has a band gap of 1.6
electron volts with organic as well as inorganic components. However, it is
very difficult to provide the perovskite layer with a transparent front
contact. While sputter deposition of indium tin oxide (ITO) is common practice
for inorganic silicon solar cells, this technique destroys the organic
components of a perovskite cell.
Graphene as
transparent front contact:
Now a group headed by Prof. Norbert Nickel has introduced a
new solution. Dr. Marc Gluba and PhD student Felix Lang have developed a
process to cover the perovskite layer evenly with graphene. Graphene consists
of carbon atoms that have arranged themselves into a two-dimensional honeycomb
lattice forming an extremely thin film that is highly conductive and highly
transparent.