The researchers achieved this by using a very simple post-annealing process which enabled them to create a flexible organic cell that is highly efficient, durable, and degrades by less than 5% after 3,000 in atmospheric conditions. It also boasts an energy conversion ratio of 13%, a major indicator of solar cell performance.
Organic photovoltaics are thought by many to be a promising alternative to current silicon-based solar cells. Not only are they relatively cheap to produce, but they are also far better for the environment.
No Match for Silicon Cells
Although photovoltaic cells sound promising, researchers have struggled to match the efficiency of them with current silicon-based solar cells, which exhibit energy conversion ratios as high as 25%.
In contrast, rigid organic photovoltaic cells can achieve around 17% while ultra-thin organic photovoltaic cells rarely get past the 10-12% mark. Furthermore, ultrathin films usually degrade quickly when exposed to sunlight, oxygen, and heat—all of which are found under normal atmospheric conditions. This renders them unsuitable for use in many of the applications where they would be most beneficial, such as consumer wearables.
These are the problems that the RIKEN team sought to address.
An ultra-thin organic solar cell. Image Credit: Riken.
Achieving High Energy Conversion Efficiency
The RIKEN research team published its work and findings on March 9 in the Proceedings of the National Academy of Sciences.
Here, it is described how the new organic solar cell began with a semiconductor polymer for the donor layer which was then supplemented by a non-fullerene acceptor to increase thermal stability. The researchers then experimented with a simple post-annealing process, during which the material was heated to 150°C after initial annealing at 90°C. This, according to the research team, was a critical step in improving the durability of the cells by creating a stable interface between the layers.
“By combining a new power generation layer with a simple post-annealing treatment, we have achieved both high energy conversion efficiency and long-term storage stability in ultra-thin organic solar cells,” said Kenjiro Fukuda, one of the study’s authors.
In the end, the final product exhibited an energy conversion ratio of 13% and degraded by less than 5% after over 3,000 hours’ exposure to atmospheric conditions.
The Use of Solar Cells in High Power Applications
By demonstrating that ultra-thin organic solar cells can be both efficient and durable, the RIKEN team is hopeful that their research will pave the way for the use of these and similar solar cells in applications that require high power and stability over prolonged periods of time, even under testing conditions such as high temperature and humidity.