Mitsubishi Electric Corp developed a polycrystalline Si solar cell whose area is 15 x 15cm, thickness is 100μm and photoelectric conversion efficiency is 18%.
The solar cell was announced at the Conference on Output Reports of the Photovoltaic Technology R&D and Related Subjects in FY2008, which was hosted by Japan's New Energy and Industrial Technology Development Organization (NEDO).
In addition, Sharp Corp and Kyocera Corp disclosed the performances of their 100μm-thick solar cells. The measurements were conducted by each company.
Mitsubishi Electric
In September 2008, Mitsubishi Electric announced a 100μm-thick cell with a conversion efficiency of 17.4% at an academic conference (See related article). This time, the company realized the 18% efficiency by, for example, employing the "honeycomb texture," which reduces the reflectance on the surface of a solar cell.
The open voltage (Voc) and the short-circuit current density (Jsc) of the cell are 643mV and 38.03mA/cm2, respectively. And its fill factor (FF) is 0.736. The honeycomb texture consists of many microscopic crevices that are formed on the surface of the cell by laser patterning and wet etching.
Sharp
Sharp achieved a conversion efficiency of 18.1% with a polycrystalline Si solar cell that is 10 x 10cm in area and 100μm in thickness. It applied the "rear side passivation structure," which forms p+ and SiNx layers and evaporated aluminum electrodes on the back side of a solar cell. The Voc, Jsc and FF of the cell are 638mV, 37mA/cm2 and 0.765, respectively.
The company announced the efficiency of 17.5% at an academic conference in January 2009. This time, the shape and forming method of the p+ layer were improved to enhance the efficiency.
Kyocera
Kyocera realized a polycrystalline Si solar cell that is 15 x 15cm in area and 100μm in thickness and features a conversion efficiency of 17.1%, which is the same value announced at an academic conference in September 2008. The Voc, Jsc and FF of the cell are 613mV, 36.8mA/cm2 and 0.76.
It employs the "back contact structure," which reduces the number of electrodes on the surface of a solar cell. According to Kyocera, it can achieve a conversion efficiency of more than 18%, if the rear side passivation structure is used.
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