Sharp Corp announced that it has achieved a cell conversion efficiency of 25.1% with a crystalline silicon (Si) solar cell.
The efficiency is the second highest after the 25.6% efficiency that Panasonic Corp announced April 10, 2014. For a long period of time, the highest efficiency for a crystalline Si solar cell had been 25.0%, which the University of New South Wales (UNSW) in Australia achieved in March 1999. This time, Panasonic and Sharp broke the record at almost the same time.
Like Panasonic, Sharp used a cell combining the "heterojunction," which is made by forming an amorphous Si layer on a Si substrate, " and the "back contact structure," which forms electrodes only on the reverse side. The amorphous Si layer prevents carrier recombination on the surface of the Si substrate. And the amount of light entering the cell was increased by eliminating electrodes on the light receiving surface.
Neither Sharp nor Panasonic has decided when to start volume production of cells having the heterojunction and back contact structure.
Sharp has already applied the back contact structure to its products. And it has announced the combination of the heterojunction and back contact structure for the first time in December 2012 at a trade show in Japan. At that time, the cell conversion efficiency of its prototype was 21.7%. Then, the company improved the efficiency to 22.3% in February 2013, 24.2% in July 2013, 24.7% in October 2013, 24.9% in February 2014 and 25.1% in April 2014.
The short-circuit current density, open voltage and fill factor of the latest cell are 41.7mA/cm2, 736mV and 81.9%, respectively, with a measured area of 3.72cm2. The measurement was conducted at Japan Electrical Safety & Environment Technology Laboratories (JET).
The latest research was carried out in cooperation with Toyota Technological Institute as part of the "Research and Development of Ultimate Silicon Crystal Solar Cell" project sponsored by Japan's New Energy and Industrial Technology Development Organization (NEDO).