Enhancing quasi-2D perovskite solar cells with dicyandiamide interface engineering

Enhancing quasi-2D perovskite solar cells with dicyandiamide interface engineering
by Riko Seibo
Tokyo, Japan (SPX) Sep 07, 2025

A research group led by Professors Pengwei Li, Yanlin Song, and Yiqiang Zhang has introduced a dicyandiamide (DCD)-based molecular bridge strategy that significantly advances quasi-2D alternating-cation-interlayer (ACI) perovskite solar cells. Published in Nano-Micro Letters, the study outlines a dual-function interface engineering method that enhances both efficiency and stability by passivating defects and regulating phase distribution.

The team reported a record power conversion efficiency of 21.54% for DCD-treated devices, compared to 19.05% in control samples. DCD reduced interfacial trap density by 73%, enabling faster charge transport and lower recombination rates. Long-term testing showed treated devices retained 94% of their initial efficiency after 1200 hours, outperforming untreated cells which maintained only 84%.

The effectiveness of DCD stems from its guanidine and cyano groups. The guanidine group binds undercoordinated Pb2+ ions and fills iodide or cation vacancies, while the cyano group coordinates with Ti4+ in TiO2, reducing oxygen vacancies and strengthening perovskite/ETL interfaces. DCD also suppressed low-n phase aggregation while promoting vertically aligned high-n phases, ensuring uniform charge transport.

Spectroscopic and theoretical studies confirmed the mechanism. XPS and FTIR validated DCD interactions with Pb and Ti, while oxygen vacancy ratios dropped from 48% to 33%. Transient absorption and photoluminescence studies revealed more homogeneous phase distributions, and DFT calculations highlighted strong CN - Ti bonding, explaining the reduced trap formation.

Performance testing showed a VOC of 1.172 V, JSC of 23.08 mA cm-2, and FF of 79.6%. Trap densities decreased more than threefold, and recombination resistance increased to 20.68 kO, highlighting efficient charge extraction. The devices maintained stability under 400 hours of continuous illumination and 1200 hours of combined thermal and environmental stress.

By integrating defect passivation with phase homogenization, this approach overcomes the traditional efficiency-stability trade-off in 2D perovskite photovoltaics. The team suggests the strategy could extend to other perovskite-based optoelectronics, including LEDs and photodetectors, providing a universal platform for scalable, high-performance device engineering.

Research Report:Dicyandiamide-Driven Tailoring of the n-Value Distribution and Interface Dynamics for High-Performance ACI 2D Perovskite Solar Cells