Scientists from the University of Warwick Department of Chemistry in collaboration with spin-out company Molecular Solar have demonstrated a solar cell with an open circuit voltage of over 7 volts.  That’s enough voltage to power and recharge a standard lithium ion battery running at about 4.2 volts.

The significance is the new solar technology means portable electronic devices such as e-book readers could be re-charged on the move in low light levels and partial shading.  This qualifies as a breakthrough – a low cost organic solar cell that generates a sufficiently high voltage to recharge a lithium-ion battery directly, without the need to connect multiple individual cells in series.  A single cell wouldn’t be a set, assembled, connected and packaged into a module saving considerable expense.

These high voltage cells perform well in different light conditions including partial shade making them well matched to consumer electronic devices such as e-book readers, cameras and some mobile phones.

The technology is based on Organic PhotoVoltaic (OPV) cells, the so-called ‘third generation’ of solar technology, offering exciting opportunities thanks to the potential for very cheap manufacture, lightweight, low profile photovoltaics compatible with flexible substrates, that when added together mean they are ideally matched to portable electronic device applications.

University of Warwick’s Tim Jones Inspecting the High Voltage Organic Photovoltaic Solar Cell Research. Click image for the largest view.

Of particular interest and significance is the scientists have addressed the problem of low out-put voltage when the module is in low light levels or partial shading taking an important step towards rolling out cheap OPV cells in low-power portable electronics.

The research is detailed in the paper “Ultra-high voltage multijunction organic solar cells for low-power electronic applications” published in the journal Advanced Energy Materials.

Professor Tim Jones, one of the lead researchers at University of Warwick, along with Dr Ross Hatton and Professor Mike Shipman, said: “We have taken a big step towards cheap-to-make solar chargers which can top up your devices whenever they are being used – both indoors and out.”

The gentlemen continuing said, “A small light-weight solar charger no bigger than a credit card can be fitted to the battery of an e-book reader for example, and constantly top it up with power while you are reading it – even if you are sitting inside on the sofa. Alternatively, this kind of solar cell could be ideal for outdoor use as it is light-weight and portable.”

Looking ahead they said, “The next step is to extend this technology outside the laboratory to make cheap OPV chargers available on a commercial scale through Molecular Solar.”

The cell is a predesigned set of subcells with complex multi-layer stacks to ensure current balancing is achieved by employing optical modeling.  The optimized multijunction devices show power conversion efficiencies of up to 3.4%, which is a modest increase over the single junction devices.

Backing for the effort came from Science City Research Alliance Energy Efficiency project that provided crucial pieces of equipment used in this research and funding from the Engineering and Physical Science Research Council and the Technology Strategy Board.

The collaborating company Molecular Solar is soon to launch a new round of fund-raising to support the commercialization of the technology.

The efficiency isn’t record shattering or even of particular note.  But the path to commercial use is a breakthrough in cost and direct applications.  The technology may well make some ides that haven’t been very interesting in the past quite interesting for the future.  Some GPS applications, weather monitoring, some types of personal signaling and the list goes on . . .


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