EMPA achieves improved efficiencies for bifacial CIGS cells

A team at Swiss research institute EMPA (Swiss Federal Laboratories for Materials Testing and Research) has developed a process that can significantly increase the efficiencies of bifacial thin-film solar cells based on copper indium gallium diselenide (CIGS). In a low-temperature production process, 19.8 percent for the front side and 10.9 percent for the back side were achieved.
In general, CIGS efficiencies - also for monofacial cells - are significantly lower than those of crystalline solar cells. Due to production conditions, this difference is even greater for bifacial cells, because the deposition of the CIGS semiconductor on a substrate is a high-temperature process that is incompatible with the use of a rear contact made of a transparent conductive oxide, which is required for bifaciality. Until now, therefore, only 9.0 percent for the front side and 7.1 percent for the back side have been achieved for bifacial CIGS cells, according to EMPA.
With the process now developed, the team also succeeded in producing a bifacial CIGS solar cell on a flexible and lightweight polymer substrate for the first time. In addition, the researchers were able to produce a bifacial tandem solar cell from CIGS and perovskite. Here, the EMPA experts see potential for efficiencies of more than 33 percent.

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