Dual channel operation upon n-channel percolation in a pentacene-C60 ambipolar organic thin film transistor

Two-Dimensional Conjugated Polymers: a New Choice For Organic Thin-Film Transistors

Organic thin-film transistors (OTFTs) as a vital component among transistors have shown great potential in smart sensing, flexible displays, and bionics due to their flexibility, biocompatibility and customizable chemical structures. Even though linear conjugated polymer semiconductors are common for constructing channel materials of OTFTs, advanced materials with high charge carrier mobility, tunable band structure, robust stability, and clear structure-property relationship are indispensable for propelling the evolution of OTFTs. Two-dimensional conjugated polymers (2DCPs), featured with conjugated lattice, tailorable skeletons, and functional porous structures, match aforementioned criteria closely. In this review, we firstly introduce the synthesis of 2DCP thin films, focusing on their characteristics compatible with the channels of OTFTs. Subsequently, the physics and operating mechanisms of OTFTs and the applications of 2DCPs in OTFTs are summarized in detail. Finally, the outlook and perspective in the field of OTFTs using 2DCPs are provided as well.

Interface Engineering in Organic Field-Effect Transistors: Principles, Applications, and Perspectives

Heterogeneous interfaces that are ubiquitous in optoelectronic devices play a key role in the device performance and have led to the prosperity of today's microelectronics. Interface engineering provides an effective and promising approach to enhancing the device performance of organic field-effect transistors (OFETs) and even developing new functions. In fact, researchers from different disciplines have devoted considerable attention to this concept, which has started to evolve from simple improvement of the device performance to sophisticated construction of novel functionalities, indicating great potential for further applications in broad areas ranging from integrated circuits and energy conversion to catalysis and chemical/biological sensors. In this review article, we provide a timely and comprehensive overview of current efficient approaches developed for building various delicate functional interfaces in OFETs, including interfaces within the semiconductor layers, semiconductor/electrode interfaces, semiconductor/dielectric interfaces, and semiconductor/environment interfaces. We also highlight the major contributions and new concepts of integrating molecular functionalities into electrical circuits, which have been neglected in most previous reviews. This review will provide a fundamental understanding of the interplay between the molecular structure, assembly, and emergent functions at the molecular level and consequently offer novel insights into designing a new generation of multifunctional integrated circuits and sensors toward practical applications.

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.

Epitaxial Growth of an Organic p-n Heterojunction: C60 on Single-Crystal Pentacene

Designing molecular p-n heterojunction structures, i.e., electron donor-acceptor contacts, is one of the central challenges for further development of organic electronic devices. In the present study, a well-defined p-n heterojunction of two representative molecular semiconductors, pentacene and C60, formed on the single-crystal surface of pentacene is precisely investigated in terms of its growth behavior and crystallographic structure. C60 assembles into a (111)-oriented face-centered-cubic crystal structure with a specific epitaxial orientation on the (001) surface of the pentacene single crystal. The present experimental findings provide molecular scale insights into the formation mechanisms of the organic p-n heterojunction through an accurate structural analysis of the single-crystalline molecular contact.

Solution-processed n-type fullerene field-effect transistors prepared using CVD-grown graphene electrodes: improving performance with thermal annealing

Solution-processed organic field effect transistors (OFETs) have generated significant interest as key elements for use in all-organic electronic applications aimed at realizing low-cost, lightweight, and flexible devices.

Solution-grown organic single-crystalline p-n junctions with ambipolar charge transport

Organic single-crystalline p-n junctions are grown from mixed solutions. First, C60 crystals (n-type) form and, subsequently, C8-BTBT crystals (p-type) nucleate heterogeneously on the C60 crystals. Both crystals continue to grow simultaneously into single-crystalline p-n junctions that exhibit ambipolar charge transport characteristics. This work provides a platform to study organic single-crystalline p-n junctions.

Diffusion-controlled growth of molecular heterostructures: fabrication of two-, one-, and zero-dimensional C(60) nanostructures on pentacene substrates

A variety of low dimensional C60 structures has been grown on supporting pentacene multilayers. By choice of substrate temperature during growth the effective diffusion length of evaporated fullerenes and their nucleation at terraces or step edges can be precisely controlled. AFM and SEM measurements show that this enables the fabrication of either 2D adlayers or solely 1D chains decorating substrate steps, while at elevated growth temperature continuous wetting of step edges is prohibited and instead the formation of separated C60 clusters pinned at the pentacene step edges occurs. Remarkably, all structures remain thermally stable at room temperature once they are formed. In addition the various fullerene structures have been overgrown by an additional pentacene capping layer. Utilizing the different probe depth of XRD and NEXAFS, we found that no contiguous pentacene film is formed on the 2D C60 structure, whereas an encapsulation of the 1D and 0D structures with uniformly upright oriented pentacene is achieved, hence allowing the fabrication of low dimensional buried organic heterostructures.