Antiphase Boundaries Regulate Phase Stability and Performance in DMA⁺-Assisted CsPbI₃-Based Perovskites

Area of Science:

• Materials Science
• Renewable Energy
• Solid-State Physics

Background:

• Cesium lead iodide (CsPbI₃) perovskites offer an ideal bandgap for tandem solar cells.
• Phase instability from photoactive γ-CsPbI₃ to non-photoactive δ-CsPbI₃, driven by microstructural defects, hinders performance.
• Ruddlesden-Popper antiphase boundaries (RP-APBs) are prevalent defects influencing strain, moisture ingress, ion migration, and recombination.

Purpose of the Study:

• To systematically regulate RP-APB defects in γ-CsPbI₃ thin films.
• To elucidate the impact of RP-APBs on phase stability and optoelectronic properties.
• To develop strategies for enhancing the stability and efficiency of CsPbI₃-based solar cells.

Main Methods:

• Investigated compositional strategies with excess PbI₂ to reduce RP-APBs.
• Employed a dimethylammonium (DMA⁺)-assisted phase-engineering approach.
• Analyzed the influence of RP-APB density on film properties and device performance.

Main Results:

• Excess PbI₂ reduced RP-APBs but induced δ-phase nucleating motifs.
• DMA⁺-assisted strategy formed β-(DMA,Cs)PbI₃, suppressing RP-APBs and preserving the perovskite framework.
• RP-APB-free β-phase films showed extended carrier lifetimes, reduced nonradiative recombination, and low trap densities.
• Achieved a champion power conversion efficiency of 20.23% with enhanced operational, thermal, and ambient-air stability.

Conclusions:

• Regulating crystalline defects, specifically RP-APBs, is crucial for stable and efficient perovskite solar cells.
• The DMA⁺-assisted strategy offers a viable route to defect-free CsPbI₃ films.
• Controlling microstructural defects is a critical factor for advancing perovskite solar cell technology.