Record claimed for solar cell efficiency

Heliatek GmbH has set a new world record for organic solar cells after Fraunhofer ISE CalLab certified a cell efficiency of 9.8% for a 1.1 cm² tandem cell manufactured with a low-temperature deposition process.

A year ago, the company set a world record for efficiency of 8.3% for an active surface of 1.1 cm². Now it has moved 1.5% in cell efficiency, to 9.8%. This new record was measured and certified by the independent Fraunhofer ISE CalLab (Freiburg, Germany) under standard test conditions.

Heliatek is said to be the only solar company in the world focused on the deposition of small molecules with low-temperature processes, a method that has already been widely adopted by the market for use with organic LEDs (OLEDs). The company develops and synthesises in-house the molecules responsible for capturing light in solar cells and converting this light into electricity. Organic solar cells have now reached the level of efficiency of conventional solar cells made from amorphous silicon.”

The company has both its own chemistry research department as well as a physics research department. This combination allows simultaneous work on material quality and cell design. It was able to optimise the absorber layer system of the record-breaking cells through synthesising the right materials. Furthermore, by improving the deposition process, cell morphology was improved, leading to an increase in power output and in fill factor.

The new cell construction will gradually be integrated into the company’s manufacturing process after the scheduled start of production in the second half of 2012. In-house measurements have shown that scaling up the cells to a panel with a size factor >120 results in an efficiency over 9% for the active module area.

The next step on the way to 15% will be a cell with over 10% efficiency sometime this year.

The flexible, thin and light panels open up new fields of applications that were so far impossible to address with conventional PV technologies. The company plans to expand production capacity with additional manufacturing lines. This will allow it to market high-performance panels into new areas, such as windows and facades.

Organic photovoltaic technology is the third generation of solar technology, after classic crystalline and thin film solar technology. OPV can be divided into two approaches: polymer-based (large molecules) and oligomer-based (small molecules) OPV, such as those used at Heliatek. The advantage of the company’s technology based on small molecules lies in better process control, higher efficiency and longer lifespan.

Its patents cover the production of organic solar cells with doped transport layers. Using tandem cell (two solar cells stacked on top of each other) it is possible to absorb a very broad solar spectrum using extremely thin organic layers, 500 nm. Coordinated activities in chemical synthesis and device physics result in a sharp climb in technological progress.

The company plans to use a low-temperature roll-to-toll process to fabricate solar panels, a process that is cost efficient in mass production. Since ‘small molecules’ have already replaced the use of polymers in the organic electronics industry (OLED displays and lighting), the company can benefit from its manufacturing experience.

The solar panels will offer four major key benefits compared with conventional panels, thus opening up new dimensions for the application of solar technology:

As the low process temperatures allow the use of plastic film as substrate material, the modules will be flexible, ultrathin and lightweight. The modules at only 0.5 kg/m² (versus 12 to 17 kg/m² for conventional PV) provide solar options for all kinds of mobile applications and for roofs with low bearing loads.

The great design freedom offers various choices in module colour, dimensions and transparency levels. Windows with semitransparent OPV can perform a dual function of solar energy collection and shading, and they can even be made with a range of tints to suit the architect’s design requirements.

The modules excel in performance compared with common solar panels. Whereas the efficiency of traditional solar modules drops off as the temperature rises, these OPV modules maintain efficiency independent of the module temperature.

Similarly, if the light intensity decreases, average modules become less efficient yet these panels have the same efficiency from full sun down to a tenth of full sun, typical for very cloudy winter days.

Organic solar technology is the truly green solar technology. The solar cells are made of fully organic, readily available material and they do not contain any known toxic ingredients or heavy metals.

Only 1 gram of organic material is required to produce one square metre of solar panel. The non-toxic manufacturing process is environmentally friendly as it doesn’t require any solvents or high input of energy. Transport costs with their associated carbon footprint are also less for the ultralightweight panels compared with common modules with their heavy, fragile sheets of protective glass.