A new breakthrough in polymer photovoltaic cells could pave the way for the development of large-scale, flexible solar devices that are easier to install upon building exteriors.

While polymer solar cells have long held promise as an economic alternative to silicon-based photovoltaic devices with a broader range of applications due to their flexibility, adoption of the technology has thus far been impeded by the fullerenes needed by the cells achieve high efficiency levels.

The fullerenes increase efficiency of the polymer cells by separating charge carriers, but suffer from the fatal defect for a photovoltaic device of becoming unstable when exposed to illumination. An added drawback is their susceptibility to the formation of large crystals at high temperatures.

Researchers from China and Sweden have developed a solar cell which possesses a record-breaking level of efficiency for a polymer photovoltaic device free of fullerenes. The invention could pave the way for cheap and reliable solar PV devices that are easier to install on curved or irregular building surface due to the flexibility of the polymer materials.

The fullerene-free polymer developed by a team of chemists led by Professor Jianhui Hou at the Chinese Academy of Sciences achieved a solar energy conversion efficiency of 11 per cent - equivalent to those of photovoltaic cells that do contain the substance.

Researchers from Sweden's Linkoping University have investigated the photovoltaic performance of the solar cells as well as proposed other methods for further improving performance.

"We have demonstrated that it is possible to achieve a high efficiency without using fullerene, and that such solar cells are also highly stable to heat. Because solar cells are working under constant solar radiation, good thermal stability is very important," said Feng Gao, physicist at Linkoping University's Department of Physics, Chemistry and Biology.

"The combination of high efficiency and good thermal stability suggest that polymer solar cells, which can be easily manufactured using low-cost roll-to-roll printing technology, now come a step closer to commercialisation."

The creation of solar cells that can be manufactured using roll-to-roll printing methods could dramatically increase the convenience of installing large-scale photovoltaic devices within built environments, by producing them in a thin and flexible form which is easier to transport, manipulate and manoeuvre."

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