Self‐Assembled Monolayers as Patterning Tool for Organic Electronic Devices

The patterning of functional materials represents a crucial step for the implementation of organic semiconducting materials into functional devices. Classical patterning techniques such as photolithography or shadow masking exhibit certain limitations in terms of choice of materials, processing techniques and feasibility for large area fabrication. The use of self‐assembled monolayers (SAMs) as a patterning tool offers a wide variety of opportunities, from the region‐selective deposition of active components to guiding the crystallization direction. Here, we discuss general techniques and mechanisms for SAM‐based patterning and show that all necessary components for organic electronic devices, i.e., conducting materials, dielectrics, organic semiconductors, and further functional layers can be patterned with the use of self‐assembled monolayers. The advantages and limitations, and potential further applications of patterning approaches based on self‐assembled monolayers are critically discussed.     

Precise Patterning of Organic Single Crystals via Capillary‐Assisted Alternating‐Electric Field

Owing to the extraordinary properties, organic micro/nanocrystals are important building blocks for future low‐cost and high‐performance organic electronic devices. However, integrated device application of the organic micro/nanocrystals is hampered by the difficulty in high‐throughput, high‐precision patterning of the micro/nanocrystals. In this study, the authors demonstrate, for the first time, a facile capillary‐assisted alternating‐electric field method for the large‐scale assembling and patterning of both 0D and 1D organic crystals. These crystals can be precisely patterned at the photolithography defined holes/channels at the substrate with the yield up to 95% in 1 mm². The mechanism of assembly kinetics is systematically studied by the electric field distribution simulation and experimental investigations. By using the strategy, various organic micro/nanocrystal patterns are obtained by simply altering the geometries of the photoresist patterns on substrates. Moreover, ultraviolet photodetectors based on the patterned Alq3 micro/nanocrystals exhibit visible–blind photoresponse with high sensitivity as well as excellent stability and reproducibility. This work paves the way toward high‐integration, high‐performance organic electronic, and optoelectronic devices from the organic micro/nanocrystals.     

Precise Patterning of Laterally Stacked Organic Microbelt Heterojunction Arrays by Surface‐Energy‐Controlled Stepwise Crystallization for Ambipolar Organic Field‐Effect Transistors

Ambipolar organic field‐effect transistors (OFETs) combining single‐crystalline p‐ and n‐type organic micro/nanocrystals have demonstrated superior performance to their amorphous or polycrystalline thin‐film counterparts. However, large‐area alignment and precise patterning of organic micro/nanocrystals for ambipolar OFETs remain challenges. Here, a surface‐energy‐controlled stepwise crystallization (SECSC) method is reported for large‐scale, aligned, and precise patterning of single‐crystalline laterally stacked p–n heterojunction microbelt (MB) arrays. In this method, the p‐ and n‐type organic crystals are precipitated via a stepwise process: first, the lateral sides of prepatterned photoresist stripes provide high‐surface‐energy sites to guide the aligned growth of p‐type organic crystals. Next, the formed p‐type crystals serve as new high‐surface‐energy positions to induce the crystallization of n‐type organic molecules at their sides, thus leading to the formation of laterally stacked p–n microbelts. Ambipolar OFETs based on the p–n heterojunction MB arrays exhibit balanced hole and electron mobilities of 0.32 and 0.43 cm² V^?1 s^?1, respectively, enabling the fabrication of complementary‐like inverters with large voltage gains. This work paves the way toward rational design and construction of single‐crystalline organic p–n heterojunction arrays for high‐performance organic, integrated circuits.