Grain boundaries contribute to the performance of perovskite solar cells by promoting charge separations

In a recent study published in Nano-Micro Letters, a collaboration led by Prof. Wenming Tian and Prof. Shengye Jin (Dalian Institute of Chemical Physics, CAS) and Prof. Yantao Shi (Dalian University of Technology) challenges the long-held belief that grain boundaries (GBs) in perovskite solar cells (PSCs) are detrimental to performance. Using operando, sub-micrometer imaging, the team reveals that GBs in high-efficiency devices can act as charge-separation “highways,” boosting photocurrent and aiding carrier extraction.

Why This Research Matters

• Direct evidence in operating devices: High-resolution confocal photoluminescence and photocurrent imaging show enhanced photocurrent at GBs with a clear anti-correlation to PL intensity—evidence of GB-driven charge separation.
• Built-in electric fields: Kelvin probe force microscopy detects strong local fields (10²–10³ V·cm⁻¹) at GBs, while transient absorption microscopy confirms ultrafast electron–hole separation (~167 ps) and a threefold longer lifetime of separated states at GBs (~14.5 ns) compared to grain interiors (~5.0 ns).
• Performance correlation: Devices with higher efficiencies (up to 22.45% PCE) exhibit greater GB-induced photocurrent enhancement (~5%) than lower-performing devices (~1.4%).
• Design insight: Rather than eliminating GBs, engineer them—passivate traps but preserve beneficial built-in fields to enhance carrier extraction.

Innovative Design and Mechanisms

• Operando correlative mapping: Custom-built imaging on thin ITO substrates achieves ~300 nm PL and ~500 nm photocurrent resolution in full device stacks, capturing real GB effects under realistic, bias-free conditions.
• Field-guided transport: GB-induced band bending channels electrons and repels holes, creating preferential carrier pathways and reducing recombination.
• Processing–function link: Adjusting annealing times modifies GB crystallinity and defect density, tuning the local electric field and net performance contribution.

Applications and Future Outlook

• Perovskite film optimization: Focus on GB engineering rather than removal to maximize their positive role in high-PCE devices.
• Module manufacturing: The operando imaging approach offers a powerful screening tool for scalable production.
• Cross-material relevance: The GB-field concept can extend to other polycrystalline optoelectronics such as CdTe, CIGS, and thin-film transistors.

By reframing grain boundaries from a problem to a design opportunity, this work provides a new direction for advancing perovskite photovoltaics toward higher efficiency and stability.