A research team at the Chinese Academy of Sciences (CAS) has achieved a power conversion efficiency of 10.3% for a solar cell based on a selenium absorber.
The result represents a world record for this photovoltaic technology and marks the first time it has exceeded the 10% efficiency threshold.
“Compared with many other photovoltaic materials, 10% may sound decent but not particularly impressive. However, selenium’s wider bandgap results in a much lower theoretical maximum efficiency,” Rasmus Nielsen, a selenium solar cell specialist at the Technical University of Denmark, told pv magazine.
“When device performance is instead compared relative to the maximum efficiency potential, selenium reaches an impressive 41.1%, outperforming antimony sulfide Sb2(S,Se)3 and even amorphous silicon (a-Si:H), despite decades of research and industrial development. In my view, this new record marks an important milestone, and this irresistibly simple semiconductor should be taken seriously as a promising wide-bandgap absorber for tandem solar cells and indoor PV.”
Details of how the Chinese team achieved the efficiency record were outlined by Nielsen and his colleague Peter Christian Kjærgaard Vesborg in a short paper, “Selenium hits double digits,” published in nature energy.
First, the researchers replaced the titanium oxide (TiO₂) electron-selective contact with Zn₀.₈₅Mg₀.₁₅O (ZnMgO), a magnesium-doped zinc oxide alloy commonly used in optoelectronics. The material was found to be better aligned with the selenium absorber, improving band alignment and leading to a higher open-circuit voltage.
Second, conventional thermal annealing was replaced with visible-light LED illumination to crystallise the as-deposited selenium thin film. “This approach was first explored in combination with thermal annealing and later by our group using only a laser to crystallise the absorber, with light-driven crystallisation significantly improving cell morphology and, ultimately, the fill factor,” Nielsen said.
In a third step, the researchers thermally annealed the complete device after deposition of all layers. “We reported this strategy, which I called closed-space annealing (CSA), in 2024, showing that it improves carrier collection efficiency and thus both the short-circuit current density and fill factor,” Nielsen added.
According to Nielsen, the careful optimization and combination of all three strategies enabled the team to surpass the 10% efficiency threshold.
The device also achieved an open-circuit voltage of 1.03 V. In addition, unencapsulated cells showed “negligible” efficiency loss after 1,000 hours of maximum-power-point tracking under ambient conditions.
The new cell design was presented in the paper “Illumination-assisted annealing enables selenium solar cells with open-circuit voltage over 1 V and efficiency exceeding 10%,” which was also published in nature energy.
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