Monolayer Organic Crystals for Ultrahigh Performance Molecular Diodes

Molecular diodes are of considerable interest for the increasing technical demands of device miniaturization. However, the molecular diode performance remains contact-limited, which represents a major challenge for the advancement of rectification ratio and conductance. Here, it is demonstrated that high-quality ultrathin organic semiconductors can be grown on several classes of metal substrates via solution-shearing epitaxy, with a well-controlled number of layers and monolayer single crystal over 1 mm. The crystals are atomically smooth and pinhole-free, providing a native interface for high-performance monolayer molecular diodes. As a result, the monolayer molecular diodes show record-high rectification ratio up to 5 × 108 , ideality factor close to unity, aggressive unit conductance over 103 S cm-2 , ultrahigh breakdown electric field, excellent electrical stability, and well-defined contact interface. Large-area monolayer molecular diode arrays with 100% yield and excellent uniformity in the diode metrics are further fabricated. These results suggest that monolayer molecular crystals have great potential to build reliable, high-performance molecular diodes and deeply understand their intrinsic electronic behavior.

Graphene-Quantum-Dots-Induced Centimeter-Sized Growth of Monolayer Organic Crystals for High-Performance Transistors

Monolayer organic crystals have attracted considerable attention due to their extraordinary optoelectronic properties. Solution self-assembly on the surface of water is an effective approach to fabricate monolayer organic crystals. However, due to the difficulties in controlling the spreading of organic solution on the water surface and the weak intermolecular interaction between the organic molecules, large-area growth of monolayer organic crystals remains a great challenge. Here, a graphene quantum dots (GQDs)-induced self-assembly method for centimeter-sized growth of monolayer organic crystals on a GQDs solution surface is reported. The spreading area of the organic solution can be readily controlled by tuning the pH value of the GQDs solution. Meanwhile, the π-π stacking interaction between the GQDs and the organic molecules can effectively reduce the nucleation energy of the organic molecules and afford a cohesive force to bond the crystals, enabling large-area growth of monolayer organic crystals. Using 2,7-didecyl benzothienobenzothiopene (C₁₀-BTBT) as an examples, centimeter-sized monolayer C₁₀-BTBT crystal with uniform molecular packing and crystal orientation is attained. Organic field-effect transistors based on the monolayer C₁₀-BTBT crystals exhibit a high mobility up to 2.6 cm² V^-1 s^-1, representing the highest mobility value for solution-assembled monolayer organic crystals. This work provides a feasible route for large-scale fabrication of monolayer organic crystals toward high-performance organic devices.