Date: 15/02/2013

Panasonic's HIT solar PV cell touches conversion effeciency of 24.7%

Solar PV engineers at Panasonic have achieved a record conversion efficiency of 24.7% at the research level, using its HIT solar cell at 98 µm thickness. The rate is the world's highest for any crystalline silicon-based solar cell of practical size (100 cm² and above), claims Panasonic.

Panasonic says the latest figure is 0.8 percentage points higher than the previous record (23.9%) for HIT solar cells, and 0.5 percentage points higher than the previously published record for any monocrystalline silicon-based solar cell of practical size (100 cm² and above).

Panasonic explains below the core technologies behind the record efficiency rating:

(1) Reduction in recombination loss
A key feature of HIT solar cells is the lamination of a high-quality amorphous silicon layer onto the surface of the monocrystalline silicon substrate that serves as the power-generating layer. This leads to a reduction in recombination loss within the electrical elements, known as carriers. To further enhance this unique property of HIT solar cells, Panasonic has developed a new technology that enables to form on the monocrystalline silicon substrate an amorphous silicon layer of even higher quality while limiting damage to the surface of the substrate. This has enabled a further reduction of recombination losses within the carrier. As a result, the open voltage (Voc) has been improved from 0.748 V to 0.750 V.

(2) Reduction in optical loss
In order to achieve a high electrical current from solar cells, it is necessary to induce the solar rays arriving at the cell surface into the monocrystalline silicon substrate that serves as the power-generating layer with as little losses as possible. This time, using a HIT solar cell, Panasonic has successfully reduced absorption loss of light in the transparent conductive coatings and the amorphous silicon layer covering the monocrystalline silicon substrate. At the same time, shading loss has also been decreased by reducing the surface area of the grid electrode on the cell surface. As a result, density of the short-circuit current (Jsc) has been improved from 38.9 mA/cm² to 39.5 mA/cm².

(3) Reduction in resistive loss
In solar cells, the electrical current generated is accumulated within the grid electrode on the cell surface and then delivered outside. This time, Panasonic has succeeded in cutting down resistive loss that occurs when an electric current passes through the grid electrode by improving the grid electrode, including the development of an electrode with a higher aspect ratio. As a result, the fill factor (FF)*9 has been improved from 0.822 to 0.832.

Properties of HIT solar cells:
Open voltage (Voc): 0.750 V
Short-circuit current (Isc) [short-circuit current density (Jsc): *7 4.02 A [39.5 mA/cm²]
Fill factor (FF)9 0.832
Cell transfer efficiency 24.7%
Cell surface area 101.8 cm²
Author: Srinivasa Reddy N