2D Molecular Crystal Bilayer p–n Junctions: A General Route toward High‐Performance and Well‐Balanced Ambipolar Organic Field‐Effect Transistors

Abstract

Ambipolar organic field‐effect transistors (OFETs) are vital for the construction of high‐performance all‐organic digital circuits. The bilayer p–n junction structure, which is composed of separate layers of p‐ and n‐type organic semiconductors, is considered a promising way to realize well‐balanced ambipolar charge transport. However, this approach suffers from severely reduced mobility due to the rough interface between the polycrystalline thin films of p‐ and n‐type organic semiconductors. Herein, 2D molecular crystal (2DMC) bilayer p–n junctions are proposed to construct high‐performance and well‐balanced ambipolar OFETs. The molecular‐scale thickness of the 2DMC ensures high injection efficiency and the atomically flat surface of the 2DMC leads to high‐quality p‐ and n‐layer interfaces. Moreover, by controlling the layer numbers of the p‐ and n‐type 2DMCs, the electron and hole mobilities are tuned and well‐balanced ambipolar transport is accomplished. The hole and electron mobilities reach up to 0.87 and 0.82 cm2 V−1 s−1, respectively, which are the highest values among organic single‐crystalline double‐channel OFETs measured in ambient air. This work provides a general route to construct high‐performance and well‐balanced ambipolar OFETs based on available unipolar materials.

Surficial Marangoni Flow‐Induced Growth of Ultrathin 2D Molecular Crystals on Target Substrates

“…As a result, a uniform distribution of molecules occurred on the water surface, thus forming micrometer‐sized 2DMCs. Li and coworkers further enhanced the spreading of the organic solution on the water by decreasing the interfacial surface tension between the water and organic solution, and few‐layered or even monolayer 2DMCs were successfully obtained on the water surface. A common feature of the ultrathin 2DMCs obtained in these strategies is that the crystallization occurs on the liquid surface.…”

“…Therefore, an additional transfer process to the target substrate is required for the subsequent device applications. Although various methods have been developed for efficient transfer of the 2DMCs, it remains a challenge to avoid damage or contamination of the 2DMCs during the transfer process …”

“…[17][18][19][20][21][22][23] For example, Hu and coworkers demonstrated a strategy of introducing water as a growth surface to fabricate 2DMCs. Li and coworkers further enhanced the spreading of the organic solution on the water by decreasing the interfacial surface tension between the water and organic solution, [25,26] and fewlayered or even monolayer 2DMCs were successfully obtained on the water surface. As a result, a uniform distribution of molecules occurred on the water surface, thus forming micrometersized 2DMCs.…”

“…[24] In this method, when the organic solution with low surface tension was dropped on the water (a high surface tension media), the solution would spontaneously and rapidly spread on the water surface by the local surface tension gradients, which is well known as a Marangoni effect. [24][25][26][27] Herein, we report a surficial Marangoni flow-induced selfassembly (SMFIS) method for the fabrication of 2DMCs directly on target substrates. Li and coworkers further enhanced the spreading of the organic solution on the water by decreasing the interfacial surface tension between the water and organic solution, [25,26] and fewlayered or even monolayer 2DMCs were successfully obtained on the water surface.…”

Few‐Layer Organic Crystalline van der Waals Heterojunctions for Ultrafast UV Phototransistors

“…The transfer characteristics of the FETs showed a V‐shape with the two arms representing the hole and electron transport, yielding high hole and electron field‐effect mobilities ( µ FET ) of 1.4 and 0.65 cm 2 V −1 s −1 , respectively (Figure S3, Supporting Information). [ 29 ] The highly ordered nature of the few‐layer crystalline heterojunctions enables efficient charge transport, which is of great importance to realize a rapid photoresponse in optoelectronic devices. The optoelectrical properties were studied in FET configuration by using a 365 nm UV light source (light intensity: 300 µW cm −2 ).…”