Nature Photonics: Certified 25.8%! Eutectic molecular ligand stabilizes photoactive black phase perovskite

A team led by Zhi-Wen Gao of the University of Hong Kong, Yong Wang of Zhejiang University, and Bao-Min Xu of Southern University of Science and Technology published a research paper titled "Eutectic molecule ligand stabilizes photoactive black phase perovskite" in the journal Nature Photonics. Zhi-Wen Gao is the first author, and Zhi-Wen Gao, Yong Wang, and Bao-Min Xu are co-corresponding authors.

Key Highlight: This paper developed a hydrogen-bonded eutectic molecule (EM) composed of choline chloride (ChCl) and urea (urea) to modify the phase transition process, eliminate nanoscale phase impurities, and achieve efficient FA-rich triiodide perovskite. Thin-film perovskite solar cells fabricated using EM deliver a power conversion efficiency of 25.8% (certified at 25.7%) and excellent stability, with a T95 lifetime of approximately 2,000 hours.

Formamidine-rich triiodide perovskites show great promise as light-absorbing layers for next-generation photovoltaic technologies. However, the complex phase transitions during crystallization of such perovskites often lead to the formation of an undesirable hexagonal phase, which reduces solar cell efficiency and stability. Although various additives have been developed to modulate the growth and phase stability of perovskite films by passivating defects, suppressing ion migration, and improving crystallinity, fundamental strategies for promoting and stabilizing the α phase remain unresolved.

To this end, a team led by Cai Zhihao from the University of Hong Kong, Xu Baomin from the Southern University of Science and Technology, and Wang Yong from Zhejiang University used hydrogen-bonding eutectic molecules (EMs) as ligands for the [PbI6]4− octahedron to promote the dominant formation of corner-sharing octahedra. Their results demonstrate that increasing the ratio of corner-sharing to face-sharing octahedra can induce a complete phase transition and promote the formation of a pure cubic perovskite structure. Perovskite solar cells fabricated with EM-based films deliver a power conversion efficiency of 25.8% (certified at 25.7%) and excellent stability, with a T95 lifetime of approximately 2,000 hours.

This study demonstrates a novel EM with hydrogen bonding that modifies the phase transition process, enabling highly efficient FA-rich tricationic perovskites. The perovskite film combined with EM exhibits a facilitated phase transition from hexagonal to cubic phase by enhancing the energetic advantage of corner-sharing [PbI6]4− octahedra and eliminating hexagonal impurities. The proposed technique reveals the microscopic mechanism of the eutectic additive-facilitated phase transition and provides insights into the exploration of eutectic additives with tunable compositional properties.

Source：https://doi.org/10.1038/s41566-024-01596-8