Researchers advance perovskite solar cells with innovative phase-layering technique

(Nanowerk Spotlight) With the urgent need to decarbonize the global energy system, researchers around the world are racing to develop next-generation solar technologies that are ultra-low cost yet highly efficient. An especially promising candidate is perovskite solar cells - lightweight thin-film devices made from inexpensive earth-abundant materials. However, despite rapid gains in efficiency, problems with instability have hampered their path to commercial viability.
In a new study published in Nature Energy ("Phase-heterojunction all-inorganic perovskite solar cells surpassing 21.5% efficiency"), researchers have made a significant advance in perovskite solar cell efficiency by developing an innovative “phase-layering” technique that could also improve stability.
The research team led by scientists at Chonnam National University in South Korea fabricated a tandem perovskite cell by strategically stacking two different crystal polymorphs of the light-absorbing perovskite material cesium lead triiodide.
First author Dr. Sawanta Mali, from the Polymer Energy Materials Laboratory at Chonnam National University, explains to Nanowerk that by combining the distinct properties of each polymorph into a single bilayer junction, the resulting solar cell acts like a semiconductor p-n junction. This helps separate and collect photo-generated charges, boosting efficiency.
"This phase-layering technique provides a simplified approach towards efficient perovskite solar cells with high stability," said Mali.
Prof. Chang Kook Hong (left) and Dr. Sawanta S. Mali
Prof. Chang Kook Hong (left) and Dr. Sawanta S. Mali showing the all-inorganic perovskite solar cell module fabricated at the Polymer Energy Materials Laboratory, Chonnam National University, South Korea, which approaches 20% efficiency. (Image: Dr. Jyoti V. Patil)
Building traditional semiconductor p-n junctions with perovskites has proven complex, requiring elaborate processing steps. The researchers’ phase-layering method offers a much simpler route.
The key innovation was depositing the front polymorph layer using an anti-solvent-free “hot-air” technique, and the rear layer by thermal evaporation in a vacuum chamber. The researchers also introduced small amounts of chemical additives to stabilize each polymorph layer.
This enabled the fabrication of uniform, defect-free junctions between the two crystal polymorphs – something that has persistently obstructed efficiency gains.
The resulting phase heterojunction perovskite solar cells (PHS) achieved an exceptional power conversion efficiency of 21.59%, among the highest reported values for this type of cell.
In real-world tests, the cells maintained over 90% of their initial efficiency after 200 hours of operation, demonstrating their potential for stability.
By fabricating larger cells with 1 square cm active areas, the researchers achieved 19% efficiency, proving the scalability of their tandem cell design. Furthermore, they produced small solar panels with 18% efficiency over 18 square cm areas.
"Our demonstration of the formation of a dual-polymorph heterojunction has great potential in perovskite photovoltaic technologies," notes Mali.
Compared to conventional crystalline silicon solar panels that currently dominate the market, perovskite cells can be produced at much lower temperatures using inexpensive materials and manufacturing methods. This could enable ultra-low cost solar electricity.
While silicon cells are approaching their theoretical efficiency limit of around 26%, the theoretical maximum for perovskites exceeds 30%, leaving significant room for improvement.
Mali points out that their innovative phase-layering method could also be applied to multi-junction perovskite cells and other cutting-edge solar cell designs – critical to pushing efficiencies nearer to the theoretical limits.
"Our phase-layering approach provides a simplified route towards efficient and stable perovskite solar cells," he concludes. He adds that this opens up possibilities for fabricating even more complex multi-layer perovskite devices in the future.
With their compelling cost and efficiency attributes, perovskite photovoltaics appear primed to become a transformative renewable energy technology in coming years. Advancements like the polymorph phase-layering technique represent important progress along the road towards wide-scale deployment.
Michael Berger By – Michael is author of three books by the Royal Society of Chemistry:
Nano-Society: Pushing the Boundaries of Technology,
Nanotechnology: The Future is Tiny and
Nanoengineering: The Skills and Tools Making Technology Invisible
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