Selenium solar cell with optimized energy bandgap


Researchers from the Wuhan National Laboratory for Optoelectronics (WNLO) in China have fabricated a selenium (Se) solar cell with a selenium-tellurium (Se-Te) absorber, which they claim can optimize the selenium bandgap, thus improving the overall cell efficiency.

“Selenium element is a promising light-harvesting material for solar cells because of the large absorption coefficient and prominent photoconductivity,” the scientists said. “However, the efficiency of Se solar cells has been stagnated for a long time owing to the suboptimal bandgap (> 1.8 eV) and the lack of a proper electron transport layer.”

The researchers built the cell with an indium tin oxide (ITO) substrate, an electron transport layer (ETL) made of zinc-oxide (ZnO), a Se-Te absorber alloyed by using 70% of Se and 30% of Te, and a gold (Au) metal contact.

“Alloying selenium with tellurium, which has the same crystal structure and a narrow bandgap, can tune the bandgap and increase the melting point, thus expanding the absorption spectrum and improving the quality of the selenium solar cell films,” said lead author Chao Chen.

The research group pointed out the ZnO ETL as another decisive factor contributing to increase the overall cell efficiency. It is reportedly able to slightly react with selenium to enhance its interfacial adhesion and to reduce dangling bonds and thus reduce interfacial defects.

It tested the device under standard illumination conditions and found its power conversion efficiency reached 1.85%.

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“The efficiency of ZnO/Se0.7Te0.3 solar cells has more than doubled after nine months in the air,” Chen also said, noting that the next steps in the research will be prepare high-quality Se-Te alloy films, eliminate holes and vacancy defects, and optimize device structure.

The scientists said that, thanks to the Se-Te absorber, the cell open-circuit voltage decreased as expected, while the short-circuit current did not always increase due to the current loss at long wavelengths. In addition, they found the fill factor was rather low because of the cliff at the interface and the leakage according to the small shunt resistance.

“We mainly focused on the device and analyzed its air stability, defect properties and recombination mechanism, for the sake of providing guidance for the further performance optimization,” they said.

They introduced the cell technology in “Fabrication and characterization of ZnO/Se1-xTex solar cells,” which was recently published in Frontiers of Optoelectronics.

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