A group of South Korean scientists has created an organic solar cell that they say has the highest energy efficiency rate in the world.

The team led by Lee Kwang-hee at the Gwangju Institute of Science and Technology (GIST) said Friday that their solar cell has an energy efficiency rate of six-and-a-half percent.

Lee said the rate is the highest to be reached by any plastic-based organic photovoltaic solar cell, which some scientists have argued could not surpass the five percent mark. Experts have also said that an efficiency rate of seven percent must be reached for plastic solar cells to become commercially viable.

The team’s achievement was published in the latest issue of Science magazine. Professor Alan Heeger of the University of California in Santa Barbara, a Nobel Prize laureate, also joined Lee’s team as a co-researcher.

Energy efficiency indicates the percentage of sunshine that solar cells turn into electricity, and a solar, or photovoltaic cell is a device that converts that light energy into electrical energy.