Heliatek, a Germany-based photovoltaic (PV) cell manufacturer, developed an organic thin-film PV cell with a conversion efficiency of 10.7%, which is the highest level in the world.

Heliatek made an announcement about the cell April 27, 2012 (Press release). And Karl Leo, professor at the Technical University of Dresden and head of IAPP, explained the details of the cell at an international symposium that the Research Center for Organic Electronics of Yamagata University organized May 11, 2012. He is a co-developer of the cell.

The organic thin-film PV cell used for the measurement of the efficiency uses a low-molecular organic semiconductor material called oligomer. Its element has a tandem structure. When Heliatek made a unijunction element that does not have a tandem structure, its conversion efficiency was 7%.

The area of the cell used for the measurement is 1.1cm2. And the measured efficiency was certified by SGS Institut Fresenius, a Germany-based testing institution.

In general, the conversion efficiency of a silicon (Si)-based PV cell lowers with a low illuminance or at a high temperature. On the other hand, the conversion efficiency of the new PV cell increases with a low illuminance, and it hardly lowers even at a temperature of 80°C.

In December 2011, Heliatek announced the specifications of a similar cell, which were measured by Germany-based Fraunhofer ISE CatLab. At that time, the conversion efficiency, form factor (FF), open voltage (VOC) and short-circuit current of the cell were 9.75±0.3%, 68.27±0.68, 1.6930±0.0085V and 9.08±0.23mA, respectively. The latest specifications measured by SGS were realized by improving cell properties, Heliatek said.

15% efficiency by 2015

The conversion efficiencies of organic thin-film PV cells are still lower than those of inorganic thin-film PV cells. However, for the past three years, their conversion efficiencies have increased more than the conversion efficiency of any other type of PV cell. For example, in 2009, the highest efficiency of organic thin-film PV cell was 6%.

Recently, Mitsubishi Chemical Corp and the University of California, Los Angeles (UCLA) also developed organic thin-film PV cells whose conversion efficiencies are higher than 10%.

At the symposium, Yang Yang, distinguished guest research professor of Yamagata University and professor of UCLA, delivered a lecture and said, "About one year ago, the conversion efficiency of organic thin-film PV cell was higher than 8% and lower than 9%. But it is now about 11%. We can achieve an efficiency of 15% by 2015."