A team at Yunnan University, led by Hongjun Wu and colleagues, with contributing researchers from Kunming University of Science and Technology, has reported a 20.96% efficient CsPbI3-xBrx inorganic perovskite solar cell (IPSC), achieved through a new surface passivation molecule built around a sulfonamide group. The result is described as the highest efficiency reported to date for SnO2-based IPSCs, and the unencapsulated devices also showed strong long-term stability.
All-inorganic CsPbI3-xBrx perovskites are of interest for PV applications because of their thermal stability and suitability for tandem architectures, but their surfaces are prone to undercoordinated Pb2+ defects. These form when iodide ions migrate out of the lattice under heat, moisture or illumination, leaving behind halogen vacancies that act as non-radiative recombination centers and degrade both efficiency and long-term performance. To address this, the researchers introduced 4-aminomethylbenzenesulfonamide (4-AMBSA), a π-conjugated molecule carrying both an amino (-NH2) and a sulfonyl (-SO2-) group, onto the CsPbI3-xBrx surface.
The two functional groups coordinate synergistically with undercoordinated Pb2+ ions, reducing defect density, while the amino group's hydrogen-bonding interactions with iodide ions help suppress the ion migration that generates those defects in the first place. π-π stacking between 4-AMBSA molecules was also reported to promote a dense, uniform passivation layer on the perovskite surface.
With this treatment, the team measured a champion power conversion efficiency of 20.96%, along with significantly suppressed interfacial charge recombination and delayed phase decomposition of the perovskite film. Unencapsulated devices retained over 93% of their initial efficiency after 1,100 hours under a nitrogen atmosphere, which the authors note is among the top-tier stability results reported for n-i-p type IPSCs.
The authors attribute the combined efficiency and stability gains to 4-AMBSA's dual role: its coordination with Pb2+ sites lowers the defect density that drives non-radiative recombination, while its suppression of iodide migration removes the underlying source of those defects rather than just masking their effects. That distinction, the team notes, is what separates 4-AMBSA from conventional small-molecule passivators such as long-chain alkylamines or carboxylic acids, which tend to diffuse or degrade during device operation and provide only short-lived passivation.
