Boric-acid interface pushes all-perovskite tandem cell efficiency to 28.5 %

• Chinese researchers replace corrosive phosphoric anchors with boric-acid SAMs, delivering a record 28.5 % all-perovskite tandem solar cell that retains 90 % output after 500 h of light soaking.

A joint team from the Chinese Academy of Sciences’ Ningbo Institute of Materials Technology & Engineering (NIMTE) and Tsinghua University has solved one of the quiet killers of all-perovskite tandem solar cells: NiOx corrosion. In wide-bandgap (WBG) top cells, the usual phosphoric-acid anchors that tether self-assembled monolayers (SAMs) to the nickel-oxide hole-transport layer are so acidic they etch the NiOx, draining both efficiency and long-term stability. 

The researchers swapped the phosphoric acid for a gentler boric-acid group. The milder –BO₂–-Ni coordination forms stronger, more uniform bonds with NiOx, preventing the molecular aggregation that plagued earlier devices. Ultrafast spectroscopy and XPS analysis confirm that the boric-acid SAM sharply reduces nickel leaching and maintains tight interfacial contact under illumination and heat stress. 

Performance gains are immediate. The boric-acid-modified WBG sub-cell hits 20.1 % power-conversion efficiency. Stacked atop a 1.25 eV narrow-bandgap bottom cell, the two-terminal tandem reaches a certified 28.5 % efficiency—among the highest reported for an all-perovskite architecture. Even more striking, the encapsulated device retains 90 % of its initial output after 500 hours of maximum-power-point tracking under one-sun illumination, edging closer to the durability benchmarks demanded by commercial financiers.

Because both sub-cells are solution-processed at low temperatures, the technology lends itself to lightweight, flexible modules and roll-to-roll manufacturing. The team now plans scale-up studies and outdoor reliability testing to prove the chemistry can withstand real-world weather cycles—a key step toward moving perovskite tandems from record tables to rooftops.