Focus on the negatives: A new path to highly efficient tandem cells

Scientists at the United States National Renewable Energy Laboratory (NREL) working with the Korea Advanced Institute of Science and Technology, have demonstrated a technique which could open up new pathways to the development of commercially viable perovskite-silicon tandem solar cells.

Passivation layers are commonly added to perovskite solar cells to limit their reactivity – improving performance and stability. The NREL’s discovery involves engineering such a layer to overcome several challenges. The group focused on the negatively charged particles – anions – in the passivation layer and found adding the anion thiocyanate, mixed with iodine, could boost device performance. The thiocyanate reportedly helped increase current and the iodine improved voltage.

In the paper Efficient, stable silicon tandem cells enabled by anion-engineered wide-bandgap perovskites, published in Science, the U.S.-Korean group described perovskite-silicon tandem cells made using the novel approach. The researchers claim to have achieved 26.2% efficiency and maintained more than 80% of initial performance after 1,000 hours of continuous illumination.

The perovskite layer itself reportedly boasted an efficiency of 20.7% and the group is convinced additional work to perfect the silicon layer could mean their approach would yield tandem cells with efficiencies of more than 30% and open new possibilities for perovskite solar cell development.

“This study provides a new general approach with clear technological breakthroughs and scientific insights for further advancement of perovskite technologies,” said Kai Zhu, senior scientist in the chemistry and nanoscience center at the NREL.