Synergistic Efficiency-Stability Enhancement in Sn-Pb Narrow-Bandgap Perovskite Solar Cells via Molecular...

Area of Science:

• Materials Science
• Renewable Energy
• Solid-State Physics

Background:

• Tin-lead (Sn-Pb) mixed narrow band gap (NBG) perovskite solar cells (PSCs) are promising for tandem photovoltaics due to their tunable bandgap (~1.25 eV).
• Conventional ammonium salt passivators enhance PSC efficiency but often reduce operational stability by introducing mobile ions.
• A key challenge is balancing efficiency gains with long-term operational stability in Sn-Pb PSCs.

Purpose of the Study:

• To systematically investigate alkylammonium halide salts with varying carbon chain lengths as passivators for Sn-Pb PSCs.
• To reconcile the trade-off between efficiency enhancement and operational stability in NBG PSCs.
• To identify a passivator that offers superior defect passivation, improved crystallographic orientation, and suppressed ion migration.

Main Methods:

• Systematic investigation of alkylammonium halide salts with varying carbon chain lengths.
• Transient ion current measurements to quantify mobile ion density.
• Electrostatic potential calculations and X-ray Photoelectron Spectroscopy (XPS) for coordination analysis.
• Grazing-incidence wide-angle X-ray scattering (GIWAXS) to assess crystallographic orientation and surface morphology.

Main Results:

• Long-chain oleylammonium iodide (OAmI) demonstrated superior defect passivation, enhanced (001)-oriented crystallization, and significantly suppressed ion migration.
• OAmI treatment resulted in a fourfold reduction in mobile ion density and improved coordination with Sn²⁺/Pb²⁺ sites.
• Champion power conversion efficiency (PCE) reached 22.69% for small-area Sn-Pb PSCs and 14.46% for 6 × 6 cm² mini-modules.
• OAmI-treated devices showed a nearly twofold increase in T80 operational lifetime compared to control devices.

Conclusions:

• Oleylammonium iodide (OAmI) effectively reconciles the efficiency-stability trade-off in Sn-Pb NBG PSCs.
• OAmI acts as a synergistic passivator, improving defect passivation, crystal quality, and ion migration suppression.
• The findings pave the way for developing more stable and efficient perovskite solar cells for large-area and tandem applications.