Highly-Polarized Solar-Blind Ultraviolet Organic Photodetectors.

Developing high-performance polarization-sensitive ultraviolet photodetectors is crucial for their application in military remote sensing, detection, bio-inspired navigation, and machine vision. However, the significant absorption in the visible light range severely limits the application of polarization-sensitive ultraviolet photodetectors, such as high-quality anti-interference imaging. Here, based on a wide-bandgap organic semiconductor single crystal (trans-1,2-bis(5-phenyldithieno[2,3-b:3',2'-d]thiophen-2-yl)ethene, BPTTE), high-performance polarization-sensitive solar-blind ultraviolet photodetectors with a dichroic ratio close to 4.26 are demonstrated. The strong anisotropy of 2D grown BPTTE single crystals in molecular vibration and optical absorption is characterized by various techniques. Under voltage modulation, stable and efficient detection of polarized light is demonstrated, attributed to the intrinsic anisotropy of transition dipole moment in the bc crystal plane, rather than other factors. Finally, high-contrast polarimetric imaging and anti-interference imaging are successfully demonstrated based on BPTTE single crystal photodetectors, highlighting the potential of organic semiconductors for polarization-sensitive solar-blind ultraviolet photodetectors.

High-Efficiency Area-Emissive White Organic Light-Emitting Transistor for Full-Color Display.

The construction of high-performance white organic light-emitting transistor (OLET) with uniform area emission is crucial for smart display technologies but remains greatly challenging. Herein, high-efficiency uniform area-emissive OLETs based on a unique lateral-integrated device configuration which incorporates efficient energy transfer of phosphorescent and fluorescent guests, enabling color-tunable and white emission, are demonstrated. Through precisely regulating the energy transfer between host and guests, high external quantum efficiency of 13.9% for white-emission OLETs is achieved due to the improved high exciton utilization and light outcoupling efficiency which is the highest value reported so far for OLETs and prevents exciton-charge annihilation and electrode photon losses. Moreover, good loop stability is also achieved, along with effective gate tunability and ultralow driving voltage of below 5 V. Finally, a 4 × 6 white-emission OLET array for full-color display is demonstrated for the first time, suggesting its great potential applications for advanced display technologies.

Phase-pure 2D tin halide perovskite thin flakes for stable lasing.

Ruddlesden-Popper tin halide perovskites are a class of two-dimensional (2D) semiconductors with exceptional optoelectronic properties, high carrier mobility, and low toxicity. However, the synthesis of phase-pure 2D tin perovskites is still challenging, and the fundamental understanding of their optoelectronic properties is deficient compared to their lead counterparts. Here, we report the synthesis of a series of 2D tin perovskite bulk crystals with high phase purity via a mixed-solvent strategy. By engineering the quantum-well thickness (related to n value) and organic ligands, the optoelectronic properties, including photoluminescence emission, exciton-phonon coupling strength, and exciton binding energy, exhibit a wide tunability. In addition, these 2D tin perovskites exhibited excellent lasing performance. Both high-n value tin perovskite (n > 1) and n = 1 tin perovskite thin flakes were successfully optically pumped to lase. Furthermore, the lasing from 2D tin perovskites could be maintained up to room temperature. Our findings highlight the tremendous potential of 2D tin perovskites as promising candidates for high-performance lasers.

Organic Polarized Light-Emitting Transistors.

Electrically driven polarized light-emitting sources are central to various applications including quantum computers, optical communication, and 3D displays, but serious challenges remain due to the inevitable incorporation of complex optical elements in conventional devices. Here, organic polarized light-emitting transistors (OPLETs), a kind of novel device that integrates the functions of organic field-effect transistors, organic light-emitting diodes, and polarizers into one unique device, are demonstrated with a degree of polarization (DOP) as high as 0.97, which is comparable to completely linearly polarized light (DOP = 1). Under the modulation of gate voltage, robust and efficient polarization emission is proven, ascribed to the intrinsic in-plane anisotropy of the molecular transition dipole moment in organic semiconductors and the open-ended feature of OPLETs instead of other factors. As a result, high-contrast optical imaging and anti-counterfeiting security are successfully demonstrated based on OPLETs, establishing a new direction for photonic and electronic integration toward on-chip miniaturized optoelectronic applications.

Harvesting Triplet Excitons in High Mobility Emissive Organic Semiconductor for Efficiency Enhancement of Light-Emitting Transistors.

Organic light-emitting transistors (OLETs), a kind of highly integrated and minimized optoelectronic device, demonstrate great potential applications in various fields. The construction of high-performance OLETs requires the integration of high charge carrier mobility, strong emission, and high triplet exciton utilization efficiency in the active layer. However, it remains a significant long-term challenge, especially for single component active layer OLETs. Herein, the successful harvesting of triplet excitons in a high mobility emissive molecule, 2,6-diphenylanthracene (DPA), through the triplet-triplet annihilation process is demonstrated. By incorporating a highly emissive guest into the DPA host system, an obvious increase in photoluminescence efficiency along with exciton utilization efficiency results in an obvious enhancement of external quantum efficiency of 7.2 times for OLETs compared to the non-doped devices. Moreover, well-tunable multi-color electroluminescence, especially white emission with Commission Internationale del'Eclairage  of (0.31, 0.35), from OLETs is also achieved by modulating the doping concentration with a controlled energy transfer process. This work opens a new avenue for integrating strong emission and efficient exciton utilization in high-mobility organic semiconductors for high-performance OLETs and advancing their related functional device applications.

Molecular doped, color-tunable, high-mobility, emissive, organic semiconductors for light-emitting transistors.

Developing high-mobility emissive organic semiconductors with tunable colors is crucial for organic light-emitting transistors (OLETs), a pivotal component of integrated optoelectronic devices, but remains a great challenge. Here, we demonstrate a series of color-tunable, high-mobility, emissive, organic semiconductors via molecular doping with a high-mobility organic semiconductor, 2,6-diphenylanthracene, as the host. The well-matched molecular structures and sizes with efficient energy transfer between the host and guest enable the intrinsically high charge transport with tunable colors. High mobility with the highest value >2 cm2 V-1 s-1 and strong emission with photoluminescence quantum yield >15.8% are obtained for these molecular-doped organic semiconductors. Last, a large color gamut for constructed OLETs is up to 59% National Television System Committee standard, meanwhile with an extremely high current density approaching 326.4 kA cm-2, showing great potential for full-color smart display, organic electrically pumped lasers and other related logic circuitries.

Redistributed Current Density in Lateral Organic Light-Emitting Transistors Enabling Uniform Area Emission with Good Stability and Arbitrary Tunability.

Organic light-emitting transistors (OLETs), integrating the functions of an organic field-effect transistor (OFET) and organic light-emitting diode (OLED) in a single device, are promising for the next-generation display technology. However, the great challenge of achieving uniform area emission in OLETs with good stability and arbitrary tunability hinders their development in this field. Herein, an effective solution to obtain well-defined area emission in lateral OLETs by incorporating a charge-transport buffer (CTB) layer between the conducting channel and emitting layer is proposed. Comprehensive theoretical simulation and experimental results demonstrate redistributed potential beneath the drain electrode under the shielding effect of the CBT layer, resulting in a highly uniform current density. In this case, uniform recombination of balanced holes and electrons can be guaranteed, which is essential for the formation of area emission in the following OLETs. RGB OLETs with uniform area emission are constructed, which show good gate tunable ability (ON/OFF ratio 106 ), high loop stability (over 200 cycles) and high aperture ratio (over 80%) due to the arbitrary tunability of the device geometry. This work provides a new avenue for constructing area-emission lateral OLETs, which have great potential for display technology because of their good compatibility with conventional fabrication techniques.

Intrinsic Linear Dichroism of Organic Single Crystals toward High-Performance Polarization-Sensitive Photodetectors.

The ability to detect light in photodetectors is central to practical optoelectronic applications, which has been demonstrated in inorganic semiconductor devices. However, so far, the study of polarization-sensitive organic photodetectors, which have unique applications in flexible and wearable electronics, has not received much attention. Herein, the construction of polarization-sensitive photodetectors based on the single crystals of a superior optoelectronic organic semiconductor, 2,6-diphenyl anthracene (DPA), is demonstrated. The systematic characterization of two-dimensionally grown DPA crystals with various techniques definitely show their strong anisotropy in molecular vibration, optical reflectance and optical absorption. In terms of polarization sensitivity, DPA-crystal based photodetectors exhibit a linear dichroic ratio up to ≈1.9. Theoretical calculations confirm that intrinsic linear dichroism, originated from the anisotropic in-plane crystal structure, is responsible for the polarization sensitivity of DPA crystals. This work opens up a new door for exploiting organic semiconductors for developing highly compact polarization photodetectors and providing new functionalities in novel flexible optical and optoelectronic applications.

High Mobility Organic Lasing Semiconductor with Crystallization-Enhanced Emission for Light-Emitting Transistors.

The development of high mobility organic laser semiconductors with strong emission is of great scientific and technical importance, but challenging. Herein, we present a high mobility organic laser semiconductor, 2,7-diphenyl-9H-fluorene (LD-1) showing unique crystallization-enhanced emission guided by elaborately modulating its crystal growth process. The obtained one-dimensional nanowires of LD-1 show outstanding integrated properties including: high absolute photoluminescence quantum yield (PLQY) approaching 80 %, high charge carrier mobility of 0.08 cm2 V-1 s-1 , Fabry-Perot lasing characters with a low threshold of 86 µJ cm-2 and a high-quality factor of ≈2400. Furthermore, electrically induced emission was obtained from an individual LD-1 crystal nanowire-based light-emitting transistor due to the recombination of holes and electrons simultaneously injected into the nanowire, which provides a good platform for the study of electrically pumped organic lasers and other related ultrasmall integrated electrical-driven photonic devices.

Organic Light-Emitting Transistors Entering a New Development Stage.

Organic light-emitting transistors (OLETs) are possibly the smallest integrated optoelectronic devices that combine the switching and amplification mechanisms of organic field-effect transistors (OFETs) and the electroluminescent characteristic of organic light-emitting diodes (OLEDs). Such a unique architecture of OLETs makes them ideal for developing the next-generation display technology and electrically pumped lasers for miniaturized photonic devices and circuits. However, the development of OLETs has been slow. Recently, some exciting progress has been made with breakthroughs in high mobility emissive organic semiconductors, construction of high-performance OLETs, and fabrication of novel multifunctional OLETs. This recent slew of advances may represent the advent of a new development stage of OLETs and their related devices and circuits. In this paper, a detailed review of these fantastic advances is presented, with a special focus on the key points for developing high-performance OLETs. Finally, a brief conclusion is provided with a discussion on the challenges and future perspectives in this field.

High-performance amorphous organic semiconductor-based vertical field-effect transistors and light-emitting transistors.

Herein, two kinds of vertical organic optoelectronic devices, vertical organic field-effect transistors (VOFETs) and light-emitting transistors (VOLETs), were constructed based on amorphous organic semiconductors of N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPB) as hole injecting and transport layers and tris(8-hydroxy-quinolinato) aluminum (Alq3) as the emitting layer. High device performances with a large on/off ratio of ∼6 × 103, current density of ∼40 mA cm-2, and fast response of ∼5 ms at a frequency of 20 Hz and a brightness of 126 cd m-2 were demonstrated for these two vertical devices with good device stability and repeatability. These results suggest the potential applications of amorphous organic semiconductors with good film-forming characteristics and easy device fabrication ability in vertical optoelectronic circuits.

Organic Laser Molecule with High Mobility, High Photoluminescence Quantum Yield, and Deep-Blue Lasing Characteristics.

Here, we design and synthesize an organic laser molecule, 2,7-diphenyl-9H-fluorene (LD-1), which has state-of-the-art integrated optoelectronic properties with a high mobility of 0.25 cm2 V-1 s-1, a high photoluminescence quantum yield of 60.3%, and superior deep-blue laser characteristics (low threshold of Pth = 71 µJ cm-2 and Pth = 53 µJ cm-2 and high quality factor (Q) of ∼3100 and ∼2700 at emission peaks of 390 and 410 nm, respectively). Organic light-emitting transistors based on LD-1 are for the first time demonstrated with obvious electroluminescent emission and gate tunable features. This work opens the door for a new class of organic semiconductor laser molecules and is critical for deep-blue optical and laser applications.

High-Efficiency Single-Component Organic Light-Emitting Transistors.

Construction of high-performance organic light-emitting transistors (OLETs) remains challenging due to the limited desired organic semiconductor materials. Here, two superior high mobility emissive organic semiconductors, 2,6-diphenylanthracene (DPA) and 2,6-di(2-naphthyl) anthracene (dNaAnt), are introduced into the construction of OLETs. By optimizing the device geometry for balanced ambipolar efficient charge transport and using high-quality DPA and dNaAnt single crystals as active layers, high-efficiency single-component OLETs are successfully fabricated, with the demonstration of strong and spatially controlled light emission within both p- and n- conducting channels and output of high external quantum efficiency (EQE). The obtained EQE values in current devices are approaching 1.61% for DPA-OLETs and 1.75% for dNaAnt-based OLETs, respectively, which are the highest EQE values for single-component OLETs in the common device configuration reported so far. Moreover, high brightnesses of 1210 and 3180 cd m-2 with current densities up to 1.3 and 8.4 kA cm-2 are also achieved for DPA- and dNaAnt-based OLETs, respectively. These results demonstrate the great potential applications of high mobility emissive organic semiconductors for next-generation rapid development of high-performance single-component OLETs and their related organic integrated electro-optical devices.