Sanyo Electric Co Ltd announced July 29, 2008, that it achieved a cell conversion efficiency of 22.3% with its proprietary solar cell called "heterojunction with intrinsic thin layer (HIT) solar cell."

Although the efficiency was achieved during the research phase, the size of the cell is large enough, ie, 10cm square. In June 2007, Sanyo announced that it achieved a cell conversion efficiency of 22.0% (See related article). This time, the latest solar cell "broke the barrier of 22-percent conversion efficiency for the first time as a cell with a practical size," the company said.

The latest conversion efficiency is an official record that was measured by Japan's National Institute of Advanced Industrial Science and Technology (AIST). The cell measures 100.5cm2. It has a short-circuit current of 3.909A, an open-circuit voltage of 0.725V and a fill factor of 79.1%. The maximum power per cell is 2.242W.

Sanyo cited two key points that improved the performance of the latest cell. (1) In a HIT solar cell composed of a crystalline silicon layer sandwiched by amorphous silicon layers, the company improved the technology to wash the surface of the crystalline silicon layer prior to the formation of the amorphous silicon layers. (2) The company optimized the size and the shape of irregularities on the cell surface, which are provided to prevent reflection.

The company aims to enhance the cell conversion efficiency to 23% at the research level, and to 22% or higher at the mass-production level by fiscal 2010. The strategy for obtaining the above goals is to further pursue better results for the points (1) and (2), Kenichiro Wakisaka, a manager of Business Planning Department of Solar Division at Sanyo.

In addition, Sanyo has focused on the thickness reduction of the HIT solar cell. The company unveiled that it has reduced the thickness from the initial 300 to 200μm. "A thickness of 100μm or lower at the laboratory level was achieved," Wakisaka said.

The details of the technology will be unveiled in Sanyo's lecture at PV Japan 2008, an exhibition relating to solar cell technologies (open from July 30 to Aug. 1, 2008 at Tokyo Big Sight).