"Graphene armor" protects perovskite solar cells from damage
Perovskite is emerging as a promising material for solar cells, but it has some durability problems. Now, engineers have developed a new electrode that could make them more stable, using a protective layer of "graphene armor."
In just 10 years or so, perovskite solar cells have advanced so fast that they’ve more or less caught up to silicon’s several-decade head start, reaching efficiencies of around 20 percent. But the advantage is that perovskite is cheaper and easier to produce in bulk, and it can be printed or sprayed directly onto surfaces.
But there’s always a catch, and in this case that’s stability. Perovskite is vulnerable to being degraded by ions coming from the metal oxide electrodes in the solar cell. But now engineers at Ulsan National Institute of Science and technology (UNIST) in South Korea have found a way to protect the perovskite, and the secret ingredient is everyone’s favorite wonder material, graphene.
Graphene is a two-dimensional lattice of carbon atoms, which is transparent, super strong and electrically conductive. That makes it perfect for this purpose – it allows photons of light and electrons to pass through, but blocks metal ions.
The team’s new system is made using what they call a graphene copper grid-embedded polyimide (GCEP), which sits between the metal electrode and the perovskite. This layer allows sunlight to pass through to the perovskite to convert the energy to electrons, which are then passed back through the GCEP to the metal electrode and out to be stored and used.
In tests, the researchers showed that the new design was almost as efficient as the regular kind. Solar cells protected by the "graphene armor" had power conversion efficiencies of 16.4 percent, compared to 17.5 percent for those without. It managed to maintain that for long periods too, retaining more than 97.5 percent of that efficiency after 1,000 hours.
Other advantages were also clear. The team found that the new cells were more stable, with much less diffusion of metal ions into the perovskite layer. Plus, the graphene layer blocked UV and near-UV light, preventing the damage that those wavelengths can cause.
As an added bonus, the new solar cells are also much more flexible. After more than 5,000 bending tests, it still retained 94 percent of its initial efficiency, which could make it useful for powering wearable electronics.
The research was published in the journal Nano Letters.