Scalable Perovskite Ink Delivers 26% Air‑Coated Cells

• Air-stable DMF/NMP perovskite ink enables uniform blade-coated films and record 26.05% inverted efficiency, negligible hysteresis, and enduring high-temp stability—scaling to modules with 23.5% aperture and 96.1% GFF.

Researchers at Nanjing University, Oxford and HKUST report a DMF/NMP perovskite ink that stays stable in air for over 10,000 minutes, avoiding aggregation seen with 2‑ME/DMSO. The balanced solvent–lead interactions yield uniform, low‑defect films via blade coating. Inverted cells (6.84 mm²) hit an independently confirmed 26.05% stabilized efficiency, versus ~21.9% for the old ink, with high voltage and fill factor and negligible hysteresis.

Encapsulated cells retained ~99% efficiency after 1,700 hours at 65°C (ISOS‑L‑2), while 2‑ME/DMSO devices fell to ~43% after 500 hours; at 85°C, performance stayed ~96.9% after 1,300 hours. Mini‑modules (10–60 cm²) achieved a 96.1% geometry fill factor; a 12.6 cm² module reached 23.5% aperture efficiency (22.84% stabilized), with over 90% of 45 modules above 21%.

How did DMF/NMP inks deliver 26% cells and 23.5% mini-modules reliably?

• Tuned solvent coordination: N‑methyl‑2‑pyrrolidone (NMP) coordinates lead halides strongly enough to prevent premature cluster growth, while dimethylformamide (DMF) keeps viscosity and solubility high; the balance yields a long‑lived precursor without colloidal aggregation.
  
• Controlled crystallization kinetics: NMP’s high boiling point slows evaporation and delays perovskite nucleation, enabling blade‑coated wet films to form uniform intermediate phases that crystallize into dense, large‑grain layers with very low trap densities.
• Ambient processing window: Ink stability in room air widens the coating/annealing tolerance (temperature, humidity, line speed), reducing batch‑to‑batch drift and enabling continuous, antisolvent‑free blade coating with consistent thickness and morphology.
  
• Film quality → device metrics: Fewer deep traps and grain‑boundary defects lift open‑circuit voltage and fill factor, while uniform thickness cuts series resistance and shunts—together supporting ~26% stabilized efficiency in small‑area inverted cells with negligible hysteresis.
  
• Interface compatibility: Smooth, pinhole‑free perovskite interfaces pair well with common p‑i‑n stacks (e.g., SAM‑modified ITO hole contacts and fullerene/SnO2 electron contacts), lowering interfacial recombination and improving operational stability.
  
• Reduced residuals: The DMF/NMP route minimizes residual coordinating solvent and PbI2 islands after anneal, avoiding voids and phase inhomogeneity that typically limit scale‑up.
  
• Rheology for scale‑up: Viscosity and surface tension are tuned for high‑speed blade/slot‑die coating, giving edge‑to‑edge uniformity across tens of square centimeters without coffee‑ring effects.
  
• Module interconnects: Uniform films maintain high shunt resistance across subcells; optimized P1–P2–P3 laser scribing and narrow dead zones enable a high geometry fill factor, translating cell‑level performance to 10–60 cm² modules.
• Low loss scaling: Even current distribution and low series resistance across stripes limit aperture‑area penalties, supporting ~23.5% mini‑module efficiencies with tight device‑to‑device dispersion.
• Thermal and operational durability: Dense, low‑defect crystals and stable interfaces suppress ion migration and interdiffusion, preserving voltage and fill factor under prolonged heat/light; encapsulation then locks in moisture/oxygen barriers for reliable yield.