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Semitransparent selenium solar cell for applications in tandem devices

Scientists at the Technical University of Denmark have fabricated a bifacial selenium solar cell that can be used as a top-cell in tandem PV devices.

“Selenium (Se) is a suitable wide-bandgap absorber with a reported direct bandgap of 1.832 electronvolts for its crystallin trigonal allotrope,” the researchers explained, adding that the semiconductor has low toxicity and the potential for a low-cost fabrication process.

For the proposed cell, the Danish group used trigonal selenium that has a higher bandgap of 1.92 electronvolts and is semitransparent on both sides. 

The cell was developed in four variants: Two cells both with a thickness of 300 nm and with a monofacial and bifacial design, respectively; and two devices cells both with a thickness of 500 nm and with a monofacial and bifacial design, respectively. For the backside contact, the academics used indium tin oxide (ITO) instead of gold.

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The 300 nm bifacial device, which delivered the best performance among the four cell types, showed a power conversion efficiency of 5,2% on the front side through an n-type contact and 2.7% on the rear side through a p-type contact. Its short-circuit current was 10.96 mA for the front side and 7.40 mA on the backside, and the respective open-circuit voltage values were 0.91 and 0.88 V. The 300 nm thickness is claimed to enable an optimal fill factor of 52.6% on the front side and 41.4% on the rear side.

“It was shown how the performance from back-side illumination is more strongly dependent on the architecture of the device and also in particular on the selenium thickness,” the scientists further explained. “This is an important step toward a future Se-incorporated tandem, where it will be advantageous to invert the typical single-junction device structure before/when incorporating it into the tandem device.”

The cell is presented in the study Semitransparent Selenium Solar Cells as a Top Cell for Tandem Photovoltaics, published in RRL Solar.

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Source: pv magazine