Z Xin

Organic light-emitting transistors (OLETs) represent a new class of advanced optoelectronic devices, wherein the electrical switching capability of organic field-effect transistors (OFETs) and the light-emission capability of organic light-emitting diodes (OLEDs) are sophisticatedly integrated in a single device. On page 1252, C. Zhang, P. Chen, and W. Hu summarize the recent advancements in this important direction with respect to materials, device configurations, and operational conditions etc.

Organic light-emitting transistors (OLETs) represent an emerging class of organic optoelectronic devices, wherein the electrical switching capability of organic field-effect transistors (OFETs) and the light-generation capability of organic light-emitting diodes (OLEDs) are inherently incorporated in a single device. In contrast to conventional OFETs and OLEDs, the planar device geometry and the versatile multifunctional nature of OLETs not only endow them with numerous technological opportunities in the frontier fields of highly integrated organic electronics, but also render them ideal scientific scaffolds to address the fundamental physical events of organic semiconductors and devices. This review article summarizes the recent advancements on OLETs in light of materials, device configurations, operation conditions, etc. Diverse state-of-the-art protocols, including bulk heterojunction, layered heterojunction and laterally arranged heterojunction structures, as well as asymmetric source-drain electrodes, and innovative dielectric layers, which have been developed for the construction of qualified OLETs and for shedding new and deep light on the working principles of OLETs, are highlighted by addressing representative paradigms. This review intends to provide readers with a deeper understanding of the design of future OLETs.

Organic light-emitting transistors (OLETs), which integrate the electrical switching capability of OFETs and the light-emission capability of OLEDs in a single device, have aroused great attention from the scientific and technological communities. This review highlights recent progress in this field with respect to materials, device configurations, and operations. State-of-the-art protocols for high-performance OLETs are documented.

A uniform ultrathin polymer film is deposited over a large area with molecularlevel precision by the simple wire-wound bar-coating method. The bar-coated ultrathin films not only exhibit high transparency of up to 90% in the visible wavelength range but also high charge carrier mobility with a high degree of percolation through the uniformly covered polymer nanofibrils. They are capable of realizing highly sensitive multigas sensors and represent the first successful report of ethylene detection using a sensor based on organic field-effect transistors.

The development of transparent p-type oxide semiconductors with good performance may be a true enabler for a variety of applications where transparency, power efficiency, and greater circuit complexity are needed. Such applications include transparent electronics, displays, sensors, photovoltaics, memristors, and electrochromics. Hence, here, recent developments in materials and devices based on p-type oxide semiconductors are reviewed, including ternary Cu-bearing oxides, binary copper oxides, tin monoxide, spinel oxides, and nickel oxides. The crystal and electronic structures of these materials are discussed, along with approaches to enhance valence-band dispersion to reduce effective mass and increase mobility. Strategies to reduce interfacial defects, off-state current, and material instability are suggested. Furthermore, it is shown that promising progress has been made in the performance of various types of devices based on p-type oxides. Several innovative approaches exist to fabricate transparent complementary metal oxide semiconductor (CMOS) devices, including novel device fabrication schemes and utilization of surface chemistry effects, resulting in good inverter gains. However, despite recent developments, p-type oxides still lag in performance behind their n-type counterparts, which have entered volume production in the display market. Recent successes along with the hurdles that stand in the way of commercial success of p-type oxide semiconductors are presented.

Recent progress in hole-transporting (p-type) oxide materials and devices is reviewed. Material design strategies to improve the transport properties of five classes of oxides are discussed, including ternary Cu-bearing oxides, binary copper oxides, tin monoxide, spinel oxides, and nickel oxides. In addition, the performance of semiconductor electronic devices based on p-type oxides is reviewed, including thin-film transistors, CMOS inverters, p–n-junction diodes, memory devices, gas sensors, and electrochromics. The recent successes and the hurdles that stand in the way of commercial adoption of p-type semiconductors are discussed.

Organic thin-film transistors (OFETs) represent a promising candidate for next-generation sensing applications because of the intrinsic advantages of organic semiconductors. The development of flexible sensing devices has received particular interest in the past few years. The recent efforts of developing OFETs for sensitive and specific flexible sensors are summarized from the standpoint of device engineering. The tuning of signal transduction and signal amplification are highlighted based on an overview of active-layer thickness modulation, functional receptor implantation and device geometry optimization.

Recent efforts in developing highly sensitive and specific flexible sensors in terms of active-layer thickness modulation, functional receptor implantation, and device geometry optimization are briefly summarized with an outlook on future requirements.

A green organic light-emitting device (OLED) with an extremely high power efficiency of over 100 lm W⁻¹ is realized through energy transfer from an exciplex. An optimized OLED showed a maximum external efficiency of 25.7%, and a power efficiency of 79.4 lm W⁻¹ at 1000 cd m⁻², which is 1.6-times higher than that of state-of-the-art green thermally activated delayed fluorescence (TADF) OLEDs.

A new class of neutral bis-tridentate Ir(III) metal complexes that show nearly unitary red, green, and blue emissions in solution is prepared and employed for the fabrication of both monochrome and white-emitting organic light-emitting diodes, among which a green device gives external quantum efficiency exceeding 31%.

Ultrapure blue-fluorescent molecules based on thermally activated delayed fluorescence are developed. Organic light-emitting diode (OLED) devices employing the new emitters exhibit a deep blue emission at 467 nm with a full-width at half-maximum of 28 nm, CIE coordinates of (0.12, 0.13), and an internal quantum efficiency of ≈100%, which represent record-setting performance for blue OLED devices.

A unique design of a hexagonal boron nitride (h-BN)/HfO₂ dielectric heterostructure stack is demonstrated, with few-layer h-BN to alleviate the surface optical phonon scattering, followed by high-κ HfO₂ deposition to suppress Coulombic impurity scattering so that high-performance top-gated two-dimensional semiconductor transistors are achieved. Furthermore, this dielectric stack can also be extended to GaN-based transistors to enhance their performance.

Organic electronics have been developed according to an orthodox doctrine advocating “all-printed’’, “all-organic’’ and “ultra-low-cost’’ primarily targeting various e-paper applications. In order to harvest from the great opportunities afforded with organic electronics potentially operating as communication and sensor outposts within existing and future complex communication infrastructures, high-quality computing and communication protocols must be integrated with the organic electronics. Here, we debate and scrutinize the twinning of the signal-processing capability of traditional integrated silicon chips with organic electronics and sensors, and to use our body as a natural local network with our bare hand as the browser of the physical world. The resulting platform provides a body network, i.e., a personalized web, composed of e-label sensors, bioelectronics, and mobile devices that together make it possible to monitor and record both our ambience and health-status parameters, supported by the ubiquitous mobile network and the resources of the “cloud”.

The twinning of the signal-processing capability of traditional integrated silicon chips with printed organic electronics and sensors is debated and scrutinized, and the use of the human body as a natural local network with the bare hands as the browser of the physical world is discussed.

Planar heterojunction perovskite solar cells with a high efficiency up to 17.76% are fabricated by modifying the compact TiO₂ (c-TiO₂) with a [6,6]-phenyl-C₆₁-butyric acid (PCBA) monolayer. High quality CH₃NH₃PbI₃ films can be easily fabricated on PCBA-modified c-TiO₂ substrates by a one-step solution processing method. Significant improvements of the device parameters are observed after PCBA modification. A high open-circuit voltage (V_oc) of 1.16 V has been achieved, indicating that the PCBA monolayer can act as a hole blocking layer to reduce the trap site density atop the c-TiO₂ and the hole recombination at the c-TiO₂/perovskite interface. The enhancement of the fill factor, as well as the partial quenching of the fluorescence of perovskite after modification with PCBA, reveals that the charge extraction is improved.

Planar CH₃NH₃PbI₃ perovskite solar cells with a power conversion efficiency (PCE) of 17.76% with an open-circuit voltage of 1.16 V are fabricated by using [6,6]-phenyl-C₆₁-butyric acid (PCBA) monolayer as a hole blocking layer between compact TiO₂ layer and perovskite active layer. Compared with the control devices, PCBA monolayer modified solar cells show an 80% enhancement of PCE.

A difluorobenzoxadiazole building block is synthesized and utilized to construct a conjugated polymer leading to high-performance thick-film polymer solar cells with a V_OC of 0.88 V and a power conversion efficiency of 9.4%. This new building block can be used in many possible polymer structures for various organic electro­nic applications.