Dual-Molecule NiOx/Perovskite Passivation Boosts 27% Inverted Cells

• Dual-molecule NiOx/perovskite interface engineering—Me-4PACz plus CzOTf—locks charge extraction, passivates Pb defects, boosts voltage and stability, delivering certified 27.31% and strong 2000h/35-day retention.

Researchers from multiple Chinese and Hong Kong institutions report a dual-molecule interfacial engineering strategy for inverted (p–i–n) perovskite solar cells. The approach combines the phosphonic-acid self-assembled monolayer Me-4PACz with a cooperative modifier, 9H-carbazol-2-yl trifluoromethanesulfonate (CzOTf), to form a mixed, interface-locked molecular layer at the NiOx/perovskite junction. CzOTf is designed to stabilize charge extraction, passivate buried Pb-related defects, and relieve tensile stress that can worsen perovskite crystallization and interfacial degradation, while suppressing Ni3+-triggered redox loss pathways.

The optimized devices delivered certified 27.31% efficiency (champion 27.32%) with 1.185 V open-circuit voltage, 26.30 mA/cm² short-circuit current, and 87.64% fill factor. A CzOTf-free reference reached 26.20%. Results extended to a perovskite/silicon HJT tandem (32.84%) and large-area 766 cm² modules (21.54%). Stability improved, with 92% efficiency retention after 2000 hours under continuous light and 35 days of stable outdoor module operation.

How does Me-4PACz and CzOTf interfacial engineering boost inverted perovskite stability?

• Me-4PACz (a phosphonic-acid–based molecule) anchors strongly to the NiOx surface via the phosphonate group, creating a dense self-assembled interfacial layer that resists desorption and “locks” the interface chemistry over time.
  
• Its functional (carbazole-like) electron/charge interaction sites reduce nonradiative recombination by passivating electrically active NiOx-perovskite interface traps.
  
• The interfacial monolayer improves wetting and contact at the NiOx/perovskite boundary, promoting more uniform perovskite nucleation and a tighter, less defect-prone perovskite contact region.
  
• Me-4PACz coordination can suppress formation of under-coordinated lead and other deep-level defects near the surface, lowering trap-assisted recombination pathways that otherwise accelerate degradation.
  
• CzOTf complements Me-4PACz by pairing with the interfacial chemical environment (via its sulfonate/anion-related functionality and carbazole moiety) to further stabilize the perovskite’s near-surface defect states.
  
• CzOTf helps neutralize “buried” charge-imbalance sites formed during operation (e.g., defect formation/ion redistribution), which reduces the likelihood of interfacial charge-loss reactions.
  
• By tuning the interfacial energetics, the dual-molecule layer improves charge extraction: electrons/holes are directed more efficiently into the selective transport layers, decreasing interfacial carrier accumulation that can drive decomposition.
  
• The cooperative presence of Me-4PACz and CzOTf mitigates mechanical mismatch at the NiOx/perovskite interface, helping relieve stress that can otherwise lead to microcracks, interfacial delamination, or accelerated perovskite lattice distortion.
  
• The engineered interface acts as a barrier to ion migration (such as halides and vacancies) that commonly originates at or near the NiOx contact; slowing ion movement reduces chemical drift and interfacial phase instability.
  
• Both layers collectively reduce redox-driven degradation at the junction by lowering the population and reactivity of interfacial states that catalyze unwanted oxidation/reduction cycles.
• The result is a chemically stabilized, trap-minimized, and mechanically resilient NiOx/perovskite contact that preserves crystal quality and slows interfacial degradation under continuous illumination and outdoor conditions.