Sanyo Electric Co Ltd achieved a conversion efficiency of 22.8% with its HIT (heterojunction with intrinsic thin layer) solar cell with a thickness of 98μm, which is about half as thick as existing HIT solar cells.
Sanyo Electric realized the thinness while lowering conversion efficiency by only 0.2% (See related article). The company has not yet decided when it will start volume production of the cell.
"We can now reduce the amount of silicon used for HIT solar cells," the company said. "Silicon accounts for half the cost of those cells. So, we paved the way for lower-cost HIT solar cells."
The most prominent property of the new HIT solar cell is its open voltage (Voc), which is as high as 0.743. A solar battery with a high open voltage has excellent temperature characteristics, thus generating more electrical energy.
"It is the world's first crystalline silicon solar cell that has an open voltage higher than 0.74," Sanyo Electric said. "It will make a tumult in the academic world."
As for the other specifications of the soler cell, its short-circuit current (Isc), fill factor (FF) and cell area are 38.8mA/cm2, 79.1% and 100.3cm2, respectively. They were measured at Japan's National Institute of Advanced Industrial Science and Technology (AIST).
In general, when a solar cell becomes thin, its Voc lowers due to the carrier recombination on the surface of the silicon substrate, and its Isc also lowers because of the reduction in light absorption.
As for the first issue, HIT solar cells, which are made by accumulating amorphous silicon layers on silicon substrates, have a structure where carrier recombination rarely takes place. Sanyo Electric enhanced the voltage of its solar cell by reducing the damage on the surface of the silicon substrate when amorphous silicon layers are being formed on it.
To solve the second problem, Sanyo Electric improved the light confinement effect by reducing the optical absorption losses of the amorphous silicon layer and the transparent conductive film and making improvements to the concavo-convex shape on the surface.