High Efficiency Light-Emitting Transistor with Vertical Metal-Oxide Heterostructure

Low-Temperature Cross-Linkable Hole Transport Materials for Solution-Processed Quantum Dot and Organic Light-Emitting Diodes with High Efficiency and Color Purity

Cross-linkable hole transport materials (HTMs) are ideal for improving the performance of solution-processed quantum dot light-emitting diodes (QLEDs) and phosphorescent light-emitting diodes (OLEDs). However, previously developed cross-linkable HTMs possessed poor hole transport properties, high cross-linking temperatures, and long curing times. To achieve efficient cross-linkable HTMs with high mobility, low cross-linking temperature, and short curing time, we designed and synthesized a series of low-temperature cross-linkable HTMs comprising dibenzofuran (DBF) and 4-divinyltriphenylamine (TPA) segments for highly efficient solution-processed QLEDs and OLEDs. The introduction of divinyl-functionalized TPA in various positions of the DBF core remarkably affected their chemical, physical, and electrochemical properties. In particular, cross-linked 4-(dibenzo[b,d]furan-3-yl)-N,N-bis(4-vinylphenyl)aniline (3-CDTPA) exhibited a deep highest occupied molecular orbital energy level (5.50 eV), high hole mobility (2.44 × 10-4 cm2 V-1 s-1), low cross-linking temperature (150 °C), and short curing time (30 min). Furthermore, a green QLED with 3-CDTPA as the hole transport layer (HTL) exhibited a notable maximum external quantum efficiency (EQEmax) of 18.59% with a remarkable maximum current efficiency (CEmax) of 78.48 cd A-1. In addition, solution-processed green OLEDs with 3-CDTPA showed excellent device performance with an EQEmax of 15.61%, a CEmax of 52.51 cd A-1, and outstanding CIE(x, y) color coordinates of (0.29, 0.61). This is one of the highest reported EQEs and CEs with high color purity for green solution-processed QLEDs and OLEDs using a divinyl-functionalized cross-linked HTM as the HTL. We believe that this study provides a new strategy for designing and synthesizing practical cross-linakable HTMs with enhanced performance for highly efficient solution-processed QLEDs and OLEDs.

Recent Progress in Thin-Film Transistors toward Digital, Analog, and Functional Circuits

Thin-film transistors have been extensively developed due to their process merit: high compatibility with various substrates, large-area processes, and low-cost processes. Despite these advantages, most efforts for thin-film transistors still remain at the level of unit devices, so the circuit level for practical use needs to be further developed. In this regard, this review revisits digital and analog thin-film circuits using carbon nanotubes (CNTs), organic electrochemical transistors (OECTs), organic semiconductors, metal oxides, and two-dimensional materials. This review also discusses how to integrate thin-film circuits at the unit device level and some key issues such as metal routing and interconnection. Challenges and opportunities are also discussed to pave the way for developing thin-film circuits and their practical applications.

Improving the Performance of Red Organic Light-Emitting Transistors by Utilizing a High-k Organic/Inorganic Bilayer Dielectric

Integration of electrical switching and light emission in a single unit makes organic light-emitting transistors (OLETs) highly promising multifunctional devices for next-generation active-matrix flat-panel displays and related applications. Here, high-performance red OLETs are fabricated in a multilayer configuration that incorporates a zirconia (ZrO_x)/cross-linked poly(vinyl alcohol) (C-PVA) bilayer as a dielectric. The developed organic/inorganic bilayer dielectric renders high dielectric constant as well as improved dielectric/semiconductor interface quality, contributing to enhanced carrier mobility and high current density. In addition, an efficient red phosphorescent organic emitter doped in a bihost system is employed as the emitting layer for an effective exciton formation and light generation. Consequently, our optimized red OLETs displayed a high brightness of 16 470 cd m^-2 and a peak external quantum efficiency of 11.9% under a low gate and source-drain voltage of -24 V. To further boost the device performance, an electron-blocking layer is introduced for ameliorated charge-carrier balance and hence suppressed exciton-charge quenching, which resulted in an improved maximum brightness of 20 030 cd m^-2. We anticipate that the new device optimization approaches proposed in this work would spur further development of efficient OLETs with high brightness and curtailed efficiency roll-off.

Emerging Logic Devices beyond CMOS

Si-based complementary metal-oxide-semiconductor (CMOS) transistors for logic computing have represented the most essential foundation of digital electronic technologies for decades toward the modern information era. The continuous scaling down of the transistor feature size has promoted significant improvements in the computing performance while gradually tending to its limit. Ubiquitous intelligent technologies have quickly penetrated daily life, yielding a tremendous increase in highly data-centric computing applications. Hence, emerging logic devices extending and even transcending the existing CMOS technology are urgently needed to meet the rapidly growing demand for information processing capability, involving revolutionary innovations from material science and architecture design to device applications. This thus gives us the opportunity to realize logic devices for state-of-the-art computing that are fundamentally far beyond the current devices. In this Perspective, we discuss the recent innovative design strategies of emerging logic devices along with the opportunities and challenges, providing a promising avenue toward high-performance and diversiform logic computing in the post-Moore era.

How Materials and Device Factors Determine the Performance: A Unified Solution for Transistors with Nontrivial Gates and Transistor-Diode Hybrid Integration

Advanced field-effect transistors (FETs) with nontrivial gates (e.g., offset-gates, mid-gates, split-gates, or multi-gates) or hybrid integrations (e.g., with diodes, photodetectors, or field-emitters) have been extensively developed in pursuit for the "More-than-Moore" demand. But understanding their conduction mechanisms and predicting current-voltage relations is rather difficult due to countless combinations of materials and device factors. Here, it is shown that they could be understood within the same physical picture, i.e., charge transport from gated to nongated semiconductors. One proposes an indicator based on material and device factors for characterizing the transport and derives a unified and simplified solution for describing the current-voltage relations, current saturation, channel potentials, and drift field. It is verified by simulations and experiments of different types of devices with varied materials and device factors, employing organic, oxide, nanomaterial semiconductors in transistors or hybrid integrations. The concise and unified solution provides general rules for quick understanding and designing of these complex, innovative devices.

Recent Advances in Multi-Layer Light-Emitting Heterostructure Transistors

Light-emitting transistors (LETs) have attracted tremendous academic and industrial interest due to their dual functions of electrical switching and light emission in a single device, which can considerably reduce system complexity and manufacturing costs, especially in the area of flat panel and flexible displays as well as lighting and lasers. In recent years, enhanced LET performance has been achieved by introducing multiple-layer heterostructures in the charge-carrying/light-emitting LET channel versus the best-reported performance in single active layer LETs, rendering multi-layer LETs promising candidates for next-generation display technologies. In this review, the fundamental structures and working principles of multi-layer heterostructure LETs are introduced. Next, developments in multi-layer LETs are discussed based on co-planar LETs, non-planar LETs, and vertical LETs including organic, quantum dot, and perovskite light emitters. Finally, this review concludes with a summary and a perspective on the future of this research field.

Electrochemiluminescent Transistors: A New Strategy toward Light-Emitting Switching Devices

Light-emitting transistors (LETs) have attracted a significant amount of interest as multifunctional building blocks for next-generation electronics and optoelectronic devices. However, it is challenging to obtain LETs with a high carrier mobility and uniform light-emission because the semiconductor channel should provide both the electrical charge transport and optical light-emission, and typical emissive semiconductors have low, imbalanced carrier mobilities. In this work, a novel device platform that adapts the electrochemiluminescence (ECL) principle in LETs, referred to as an ECL transistor (ECLT) is proposed. ECL is a light-emission phenomenon from electrochemically excited luminophores generated by redox reactions. A solid-state ECL electrolyte consisting of a network-forming polymer, ionic liquid, luminophore, and co-reactant is employed as the light-emitting gate insulator of the ECLT. Based on this construction, high-performance LETs that make use of various conventional non-emissive semiconductors (e.g., poly(3-hexylthiophene), zinc oxide, and reduced graphene oxide) are successfully demonstrated. All the devices exhibit a high mobility (0.9-10 cm² V^-1 s^-1 ) and a uniform light-emission. This innovative approach demonstrates a novel LET platform and provides a promising pathway to achieve significant breakthroughs to develop electronic circuits and optoelectronic applications.

High-Performance Quantum-Dot Light-Emitting Transistors Based on Vertical Organic Thin-Film Transistors

In this work, a novel vertical quantum-dot light-emitting transistor (VQLET) based on a vertical organic thin-film transistor is successfully fabricated. Benefiting from the new vertical architecture, the VQLET is able to afford an extremely high current density, which allows most of the organic thin film transistors (OTFT) even with low mobility (for instance, poly(3-hexylthiophene)) to drive a quantum-dot light-emitting diode (QLED), which was previously unavailable. Moreover, the hole injection barrier could be modulated by the additional gate electrode, which precisely optimizes the charge balance in the device, a critical issue in QLED, resulting in the precise control of current density and brightness of the VQLET. The VQLET shows a high performance with a maximum current efficiency of 37 cd/A. Furthermore, integrating OTFT and QLED into a single device, the VQLET features drastic advantages by realizing active matrix quantum-dot light-emitting diodes (AMQLEDs), which significantly reduces the number of transistors and frees the large area fraction occupied by transistors. Hence, these results indicate that the VQLET provides a new strategy for realizing a low-cost, solution-processed, high-performance OTFT-AMQLED for the flat panel display technology. Moreover, the novel design offers a unique method to exquisitely control the charge balance and maximize the efficiency the QLED.

Electroluminescence Generation in PbS Quantum Dot Light-Emitting Field-Effect Transistors with Solid-State Gating

The application of light-emitting field-effect transistors (LEFET) is an elegant way of combining electrical switching and light emission in a single device architecture instead of two. This allows for a higher degree of miniaturization and integration in future optoelectronic applications. Here, we report on a LEFET based on lead sulfide quantum dots processed from solution. Our device shows state-of-the-art electronic behavior and emits near-infrared photons with a quantum yield exceeding 1% when cooled. We furthermore show how LEFETs can be used to simultaneously characterize the optical and electrical material properties on the same device and use this benefit to investigate the charge transport through the quantum dot film.