Perovskite solar cells (PSCs) have attracted attentions for their high-power conversion efficiency and low fabrication cost. To enhance their performance, combining three-dimensional (3D) perovskites with two-dimensional (2D) perovskite layers is a promising approach. However, liquid-based approaches often produce disordered 2D layers with mixed compositions, leading to inefficient charge extraction and limited device stability.

In a study published in Nature Synthesis. Prof. SONG Yanlin and Prof. WANG Yang's group from the Institute of Chemistry of the Chinese Academy of Sciences and Prof. ZHOU Huanping from Peking University developed a surface diffusion engineering technique which fabricates phase-pure 2D perovskite passivation layers with precisely controlled structure at the interface between the light-absorbing layer and the charge transport layer, improving the performance and stability of PSCs.

The researchers proposed a non-invasive surface reaction strategy. This solvent-free, solid-state reaction strategy addressed the challenge of mixed-dimensional formation, and achieved a pure-phase 2D perovskite contact layer with a well-defined dimensionality on top of the 3D perovskite.

Based on this strategy, the researchers fabricated high-quality perovskite films as large as 10 cm × 10 cm. And they tested seven types of organic cations including HABr, BABr, PEAI, OAI, HAI, BAI, and 4-MeO-PEAI to construct phase-pure 2D perovskite contact interfaces, which demonstrates its broad applicability.

Furthermore, the solar cells fabricated using this strategy achieved a remarkable power conversion efficiency of 26.13% (certified 25.66%), and retained full performance after 1,200 hours of continuous operation. A larger mini-module reached the efficiency of 23.03% (certified 22.32%).

"This non-invasive surface reaction strategy provides a robust and universal way for constructing well-defined 2D perovskite contact layers through solid-state diffusion, paving the way for more efficient and stable perovskite optoelectronics," said Prof. SONG.