New approach for tuning current flow in 2D MOF nanosheets shows promise for advanced electronics

Editors' notes

This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility:

fact-checked

trusted source

proofread

Researchers led by Prof. Cunlan Guo at Wuhan University have pioneered a new approach to control the electrical properties of two-dimensional (2D) metal-organic frameworks (MOFs), specifically porphyrinic 2D MOF nanosheets, by constructing molecular heterojunctions that exhibit tunable rectification behaviors. Their findings could greatly impact the development of future functional electronic devices.

In this study, published in Advanced Electronic Materials, the team paired 2D MOF nanosheets, made from tetrakis(4-carboxyphenyl) porphyrin (TCPP) and various metal ions, with oligophenylene thiol (OPT) self-assembled monolayers (SAMs) to form heterojunctions.

By adjusting the molecular length of the OPT molecules and the metal center of the MOFs, they could fine-tune the rectification ratio (RR) of the resulting devices, offering a versatile strategy for regulating electrical behaviors at the molecular level.

Notably, a remarkable rectification ratio of over 1.67 orders of magnitude was achieved with the Zn-TCPP MOF nanosheet and OPT3 SAM combination. This work opens up new avenues for the design of MOF-based electronic devices without the need for extensive synthetic modifications.

The concept of rectification—where current flows more easily in one direction than the other—is essential for the functioning of many electronic devices, from diodes to transistors. Traditionally, creating such behaviors in materials like MOFs has been challenging due to their low conductivity.

However, by leveraging the flexible molecular structures of MOFs and their inherent ability to interact with various organic ligands, the research team has introduced a new method to control these properties.

The resulting molecular heterojunctions display asymmetric current-voltage (I-V) characteristics, a hallmark of rectification. By adjusting the molecular length of the OPT and the type of metal in the MOF, the researchers were able to manipulate the alignment of energy levels at the interface of the two materials. This creates an asymmetry in charge transport, allowing for precise control over the rectification behavior, which can be tuned to suit specific applications.

The team's use of Kelvin probe force microscopy (KPFM) and first-principles calculations provided crucial insights into the energy-level alignment at the interface, enabling a deeper understanding of how molecular and metal properties influence charge transport.

The potential applications of these molecular heterojunctions are vast, extending far beyond traditional uses of MOFs. For example, the ability to manipulate rectification ratios through simple molecular adjustments offers an exciting pathway for designing next-generation functional electronic devices, such as sensors, transistors, and rectifiers, all based on MOF materials.

By demonstrating that the rectification behaviors can also be modulated through the metal coordination in TCPP—such as by incorporating iron (Fe) into the structure—the researchers have highlighted a key strategy for fine-tuning the electrical characteristics of MOFs.

These findings could also pave the way for future innovations in energy storage, catalysis, and molecular electronics, where precise control over electrical properties is critical. The success of this work underscores the promising future of MOF-based electronics, providing a flexible, tunable framework for the development of sophisticated devices with custom-tailored electrical behaviors.

More information: Bing Huang et al, Tunable Rectification in 2D Porphyrinic Metal–Organic Framework Nanosheets Molecular Heterojunctions, Advanced Electronic Materials (2024). DOI: 10.1002/aelm.202400773

Provided by Nanjing University