Graphene armor for durable solar cells
Korean scientists find 2D material has ideal solar properties Metal Tech News Weekly Edition – July 8, 2020
Last updated 7/29/2020 at 3:34am
Perovskite thin-film solar cells have been hailed as the next generation of low-cost, high-efficiency photovoltaic power generation if durability challenges can be overcome. Graphene, a two-dimensional wonder material that is finding its way into everything from virus killing sports equipment to electromagnetic radiation shields for satellite electronics, may also be the breakthrough scientist are looking for when it comes to creating more resilient perovskite solar cells.
Getting their name from the special crystal structure used to make the sunlight absorbing material, perovskite solar cells have emerged as potential replacement to traditional silicon-based cells. One of the main advantages of perovskite cells is they are cheap to produce, because they do not require the high-temperatures and precise processes that go into manufacturing silicon cells.
Perovskite thin-film cells also have the potential to be printed or coated onto surfaces, providing a multitude of applications not possible with traditional rigid cells.
Perovskite cells are also highly effective at converting sunlight into electricity, with the latest generation topping 25% efficiency. While these are tests and not commercially produced units, this is on par with the 20 to 23% efficiency of the best solar panels on the market today.
The problem, however, is that ions from a metal electrode layer degrades the perovskite, reducing the performance of these cells.
A team of researchers at the Ulsan National Institute of Science and Technology (UNIST) in South Korea have discovered that inserting a "graphene armor" between the perovskite and metal electrode prevents this degradation.
"This paper demonstrates that inserting a protection layer between the metal-based electrode and the perovskite film could prevent metal-induced degradation and that graphene, as such a layer, can effectively suppress the diffusion of metals and halide ions," says Gyujeong Jeong, a UNIST who was the first author of a study on the findings.
Other armor materials have been used but either made the thin-film cells prone to break or contained lead, which creates potential environmental issues.
Made of a single layer of carbon atoms, graphene is environmentally benign, flexible, transparent, highly conductive, and impermeable to even the smallest molecule – the perfect material for transporting electrons from the perovskite to electrode but preventing ions from contaminating the sun-catching material.
Led by Professor Hyesung Park, the UNIST team created a perovskite cell with copper polymer (copper grid-embedded polyimide) film as the electrode and a sheet of graphene as the protective layer.
This graphene armored photovoltaic cell has an efficiency of 16.1%, which is roughly on par with the average cell sold today.
This cell maintained 97.5% of the initial efficiency even after 1,000 hours of testing. It also maintained 94% efficiency after 5,000 bending tests, excellent mechanical durability that could be used to create next-generation wearable devices and other applications were flexibility is crucial.
Park said this graphene breakthrough provides an effective strategy for creating durable and efficient metal-based transparent conductive electrodes for the next generation of solar cells.
"The new method has significantly improved both the efficiency and stability of PSCs (perovskite solar cells)," the UNIST professor added.