Researchers achieve record 8.4 percent conversion efficiency in fullerene-free organic solar cells

March 11, 2014 by Hanne Degans
Imec’s novel fullerene-free OPV cell concept was used to process an OPV module (156cm2) with a conversion efficiency of 5.3%.

In this week's Nature Communications Imec presents the development of fullerene-free organic photovoltaic (OPV) multilayer stacks achieving a record conversion efficiency of 8.4 percent. This breakthrough achievement is an important step to bring organic photovoltaic cells to a higher level in the competitive thin-film photovoltaics marketplace.

Organic solar cells are an interesting thin-film photovoltaic technology due to their compatibility with flexible substrates and tunable absorption window. Although the of organic solar cells has increased rapidly in the last decade, further enhancements are needed to make the production of more easily scalable into industrial production processes. Imec's organic solar cells with record 8.4 percent power were realized by introducing two innovations. Firstly, the implementation of fullerene-free acceptor materials resulted in high open-circuit voltages and useful absorption spectra in the visible. Secondly, high short-circuit currents were achieved by developing a multilayer device structure of three active semiconductor layers with complementary , and an efficient exciton harvesting mechanism.

Fullerenes are the dominant acceptor materials in current OPV cells due to their ability to accept stable electrons and their high electron mobility. However, the small absorption overlap with the solar spectrum limits the photocurrent generation in fullerene acceptors, and their deep energy level for electron conduction limits the open-circuit voltage. Imec implemented two fullerene-free materials as acceptor, increasing open-circuit voltages compared to OPV cells with fullerene acceptors.

To increase the efficiency of organic , complex tandem architectures are often proposed to combine the exciton harvesting of multiple photo-active materials. The imec team now proposes a simple three-layer stack to improve the spectral responsivity range. This device architecture comprises two fullerene-free acceptors and a donor, arranged as discrete heterojunctions. In addition to the traditional exciton dissociation at the central donor-acceptor interface, the excitons generated in the outer acceptor layer are first relayed by energy transfer to the central acceptor, and subsequently dissociated at the donor interface. This results in a quantum efficiency above 75 percent between 400nm and 720nm. With an open-circuit voltage close to 1V, a remarkable power conversion efficiency of 8.4 percent is achieved. These results confirm that multilayer cascade structures are a promising alternative to conventional donor-fullerene .

Explore further: Charge separation understanding could result in cheaper, more efficient organic solar cells

More information: "8.4% efficient fullerene-free organic solar cells exploiting long-range exciton energy transfer." Kjell Cnops, et al. Nature Communications 5, Article number: 3406 DOI: 10.1038/ncomms4406 . Received 02 September 2013 Accepted 07 February 2014 Published 07 March 2014

Related Stories

Plastic solar cells' new design promises bright future

August 14, 2013

Energy consumption is growing rapidly in the 21st century, with rising energy costs and sustainability issues greatly impacting the quality of human life. Harvesting energy directly from sunlight to generate electricity using ...

Recommended for you

Google, EU dig in for long war

July 20, 2017

Google and the EU are gearing up for a battle that could last years, with the Silicon Valley behemoth facing a relentless challenge to its ambition to expand beyond search results.

Strengthening 3-D printed parts for real-world use

July 20, 2017

From aerospace and defense to digital dentistry and medical devices, 3-D printed parts are used in a variety of industries. Currently, 3-D printed parts are very fragile and only used in the prototyping phase of materials ...

Swimming robot probes Fukushima reactor to find melted fuel

July 19, 2017

An underwater robot entered a badly damaged reactor at Japan's crippled Fukushima nuclear plant Wednesday, capturing images of the harsh impact of its meltdown, including key structures that were torn and knocked out of place.

Microsoft cloud to help Baidu self-driving car effort

July 19, 2017

Microsoft's cloud computing platform will be used outside China for collaboration by members of a self-driving car alliance formed by Chinese internet search giant Baidu, the companies announced on Tuesday.

Making lab equipment on the cheap

July 18, 2017

Laboratory equipment is one of the largest cost factors in neuroscience. However, many experiments can be performed with good results using self-assembled setups involving 3-D printed components and self-programmed electronics. ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.