This ultrathin organic solar cell is efficient and durable
Scientists from Japan’s RIKEN institute, in collaboration with researchers from the University of Tokyo, the University of California, Santa Barbara and Monash University, have succeeded in creating an ultrathin organic solar cell that is both highly efficient and durable.
Organic photovoltaics are considered to be a promising alternative to silicon-based conventional films, being more environmentally friendly and cheap to produce. Ultrathin flexible solar cells are particularly attractive, as they could provide large power per weight and be used in a variety of useful applications such as powering wearable electronics and as sensors and actuators in soft robotics.
However, ultrathin organic films tend to be relatively inefficient, typically having an energy conversion ratio of around 10–12% — significantly lower than silicon cells, which can be as high as 25%, or of rigid organic cells, which can be up to around 17%. Ultrathin films also tend to degrade rapidly under the influence of sunlight, heat and oxygen. Researchers are trying to create ultrathin films that are both energy-efficient and durable, but it is often a difficult trade-off.
Seeking a solution, the RIKEN-led research team began with a semiconductor polymer for the ultrathin cell’s donor layer, developed by Toray Industries, and experimented with the idea of using a non-fullerene acceptor, increasing the thermal stability. On top of this, they experimented with a simple post-annealing process, where the material was heated to 150°C after an initial annealing at 90°C. This step proved to be critical in increasing the durability of the device by creating a stable interface between the layers.
The result was a flexible organic cell that degrades by less than 5% over 3000 hours in atmospheric conditions and has an energy conversion ratio of 13%. Their work has been published in the journal Proceedings of the National Academy of Sciences.
“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 ultrathin organic solar cells,” said RIKEN’s Kenjiro Fukuda, a co-author on the study.
“Our research shows that ultrathin organic solar cells can be used to supply high power in a stable way over long periods of time and can be used even under severe conditions such as high temperature and humidity. I very much hope that this research will contribute to the development of long-term stable power supply devices that can be used in wearable electronics such as sensors attached to clothes.”
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