Why all-perovskite tandem solar cells matter
Perovskite has been tested in multi-junction photovoltaic devices for years. Combined with silicon, the material has already enabled performances well beyond the limits of single-junction solar cells and the so-called Shockley-Queisser limit.
The current segment record belongs to LONGi, which achieved a 35% efficiency with an 84.3% fill factor using a 1.0028 cm² perovskite/silicon tandem cell.
One of the major advantages of synthetic perovskites is their tunability across specific light wavelengths. In silicon tandem architectures, this allows the device to capture high-energy photons that silicon alone cannot efficiently absorb, exploiting a much broader portion of sunlight.
This is also why researchers are increasingly exploring all-perovskite tandem solar cells, eliminating silicon entirely and potentially reducing some of the industry’s biggest challenges, including the high energy intensity linked to silicon manufacturing. The development is particularly relevant for emerging solar markets in Africa and other fast-growing regions seeking lower-cost and scalable renewable energy technologies.
The crystallization challenge limiting tandem efficiency
Despite their advantages, perovskites still face important technical barriers.
One of the key limitations of all-perovskite tandem photovoltaics is asynchronous crystallization inside perovskite films. Different parts of the material crystallize at different times, creating compositional and structural inhomogeneities that reduce both efficiency and long-term stability.
Chemical hardness engineering improves crystal growth
Researchers from the Ningbo Institute of Materials Technology and Engineering may now have found a solution.
The team led by Ge Ziyi and Liu Chang developed a strategy based on chemical hardness engineering to control perovskite crystal growth.
Specifically, the scientists designed additives using the hard and soft acids and bases (HSAB) theory. They identified difluoro(oxalato)borate (DFOB⁻) for wide-bandgap perovskites and tetrafluoroborate (BF₄⁻) for narrow-bandgap perovskites as effective additives.
These compounds selectively coordinate with precursor species, synchronizing crystal nucleation and growth while improving film uniformity.
Efficiency reaches 30.3%
The results are significant.
The monolithic two-terminal all-perovskite tandem solar cells achieved a certified efficiency of 30.3%, alongside an improved open-circuit voltage of 2.16 V and an 85.2% fill factor.
The devices also maintained 92% of their efficiency after 1,000 hours of maximum power point tracking.
Flexible tandem devices reached a certified efficiency of 28.2% (28.0% stabilized), opening new opportunities for lightweight and adaptable photovoltaic applications.
The findings were published in the journal Nature Nanotechnology in the paper Chemical hardness engineering synchronizes crystallization in perovskite tandems.https://www.nature.com/articles/s41565-026-02165-6