Optimizing interface engineering in quasi-2D perovskite solar cells: Enhancing performance and stability through dicyandiamide treatment

A research team led by Professors Pengwei Li, Yanlin Song, and Yiqiang Zhang has advanced quasi-2D alternating-cation-interlayer (ACI) perovskite solar cells by introducing a dicyandiamide (DCD)-based molecular bridge strategy. Their work, published in Nano-Micro Letters, demonstrates a dual-functional interface engineering approach that simultaneously passivates defects and regulates phase distribution, enabling record efficiencies and enhanced stability for 2D perovskite photovoltaics.

Why This Strategy Matters

• Efficiency Boost: DCD-modified devices achieve a power conversion efficiency (PCE) of 21.54%, compared to 19.05% in control samples.
• Reduced Defects: DCD lowers interfacial trap density by 73%, accelerating charge transport and suppressing recombination.
• Stability: Devices retain 94% of initial efficiency after 1200 h, significantly outperforming unmodified PSCs (84% retention).

Design Strategy

The innovation lies in leveraging the multifunctional guanidine and cyano groups of DCD:

• Interface Passivation: The guanidine group binds undercoordinated Pb²⁺ and fills cation/iodide vacancies at the perovskite buried interface.
• ETL Engineering: The cyano group coordinates with Ti⁴⁺ in TiO₂, eliminating oxygen vacancies and improving perovskite/ETL contact.
• Phase Regulation: DCD suppresses low-n phase aggregation while promoting high-n phase vertical alignment, leading to uniform charge transport channels.

Mechanistic Insights

Spectroscopic and theoretical analyses confirm that:

• XPS and FTIR validate DCD–Ti and DCD–Pb interactions, while reduced oxygen vacancy ratios (from 48% to 33%) highlight defect mitigation.
• Transient absorption (TA) and PL studies reveal more homogeneous phase distribution, minimizing energy transfer losses.
• DFT calculations confirm strong –CN–Ti bonding, explaining suppressed trap formation.

Performance Highlights

• Device Metrics: V_OC of 1.172 V, J_SC of 23.08 mA cm^-2, FF of 79.6%.
• Carrier Dynamics: Trap densities decreased by more than threefold; recombination resistance increased to 20.68 kΩ, confirming efficient charge extraction.
• Operational Stability: DCD-modified devices sustain performance under continuous 400 h illumination and withstand 1200 h of thermal and environmental stress.

Future Outlook

This study establishes a molecular bridge strategy that integrates defect passivation and phase homogenization, effectively decoupling the long-standing efficiency–stability trade-off in quasi-2D perovskites. Beyond solar cells, this versatile approach provides a universal platform for interface engineering in perovskite-based optoelectronics, including light-emitting diodes and photodetectors.

By uniting materials chemistry, interfacial physics, and device optimization, Professors Li, Song, and Zhang deliver a clear blueprint for the scalable development of efficient and durable next-generation perovskite photovoltaics.