Rational Design of Fluorinated 2D Polymer Film Based on Donor-Accepter Architecture toward Multilevel Memory Device for Neuromorphic Computing.

Fluorine-containing 2D polymer (F-2DP) film is a desired system to regulate the charge transport in organic electronics but rather rarely reports due to the limited fluorine-containing building blocks and difficulties in synthesis. Herein, a novel polar molecule with antiparallel columnar stacking is synthesized and further embedded into an F-2DP system to control over the crystallinity of F-2DP film through self-complementary π-electronic forces. The donor-accepter-accepter'-donor' (D-A-A'-D') structure regulates the charge transportation efficiently, inducing multilevel memory behavior through stepwise charge capture and transfer processes. Thus, the device exhibits ternary memory behavior with low threshold voltage (Vth1 of 1.1 V, Vth2 of 2.0 V), clearly distinguishable resistance states (1:102:104) and ternary yield (83%). Furthermore, the stepwise formation of the charge complex endows the device with a wider range to regulate the conductive state, which allows its application in brain-inspired neuromorphic computing. Modified National Institute of Standards and Technology recognition can reach an accuracy of 86%, showing great potential in neuromorphic computing applications in the post-Moore era.

Covalent Bond Torsion-Enabled Unique Crystal-Phase Transformation of an Organic Semiconductor for Multicolor Light-Emitting Transistors.

High-mobility and color-tunable highly emissive organic semiconductors (OSCs) are highly promising for various optoelectronic device applications and novel structure-property relationship investigations. However, such OSCs have never been reported because of the great trade-off between mobility, emission color, and emission efficiency. Here, we report a novel strategy of molecular conformation-induced unique crystalline polymorphism to realize the high mobility and color-tunable high emission in a novel OSC, 2,7-di(anthracen-2-yl) naphthalene (2,7-DAN). Interestingly, 2,7-DAN has unique crystalline polymorphism, which has an almost identical packing motif but slightly different molecular conformation enabled by the small bond rotation angle variation between anthracene and naphthalene units. More remarkably, the subtle covalent bond rotation angle change leads to a big change in color emission (from blue to green) but does not significantly modify the mobility and emission efficiency. The carrier mobility of 2,7-DAN crystals can reach up to a reliable 17 cm2 V-1 s-1, which is rare for the reported high-mobility OSCs. Based on the unique phenomenon, high-performance light-emitting transistors with blue to green emission are simultaneously demonstrated in an OSC crystal. These results open a new way for designing emerging multifunctional organic semiconductors toward next-generation advanced molecular (atomic)-scale optoelectronics devices.

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.

Universal Design and Efficient Synthesis for High Ambipolar Mobility Emissive Conjugated Polymers.

High ambipolar mobility emissive conjugated polymers (HAME-CPs) are perfect candidates for organic optoelectronic devices, such as polymer light emitting transistors. However, due to intrinsic trade-off relationship between high ambipolar mobility and strong solid-state luminescence, the development of HAME-CPs suffers from high structural and synthetic complexity. Herein, a universal design principle and simple synthetic approach for HAME-CPs are developed. A series of simple non-fused polymers composed of charge transfer units, π bridges and emissive units are synthesized via a two-step microwave assisted C-H arylation and direct arylation polymerization protocol with high total yields up to 61 %. The synthetic protocol is verified valid among 7 monomers and 8 polymers. Most importantly, all 8 conjugated polymers have strong solid-state emission with high photoluminescence quantum yields up to 24 %. Furthermore, 4 polymers exhibit high ambipolar field effect mobility up to 10-2 cm2 V-1 s-1, and can be used in multifunctional optoelectronic devices. This work opens a new avenue for developing HAME-CPs by efficient synthesis and rational design.

A Domino Protocol toward High-performance Unsymmetrical Dibenzo[d,d']thieno[2,3-b;4,5-b']dithiophenes Semiconductors.

Unsymmetric organic semiconductors have many advantages such as good solubility, rich intermolecular interactions for potential various optoelectronic applications. However, their synthesis is more challenging due to intricate structures thus normally suffering tedious synthesis. Herein, we report a trisulfur radical anion (S3⋅-) triggered domino thienannulation strategy for the synthesis of dibenzo[d,d']thieno[2,3-b;4,5-b']dithiophenes (DBTDTs) using readily available 1-halo-2-ethynylbenzenes as starting materials. This domino protocol features no metal catalyst and the formation of six C-S and one C-C bonds in a one-pot reaction. Mechanistic study revealed a unique domino radical anion pathway. Single crystal structure analysis of unsymmetric DBTDT shows that its unique unsymmetric structure endows rich and multiple weak S⋅⋅⋅S interactions between molecules, which enables the large intermolecular transfer integrals of 86 meV and efficient charge transport performance with a carrier mobility of 1.52 cm2 V-1 s-1. This study provides a facile and highly efficient synthetic strategy for more high-performance unsymmetric organic semiconductors.

High-Performance Organic Narrow Dual-Band Circular Polarized Light Detection for Encrypted Communications and Color Imaging.

Conventional circularly polarized light (CPL) detectors necessitate several optical elements, posing difficulties in achieving miniature and integrated devices. Recently developed organic CPL detectors require no additional optical elements but usually suffer from low detectivity or low asymmetry factor (g-factor). Here, an organic CPL detector with excellent detectivity and a high g-factor is fabricated. By employing an inverted quasi-planar heterojunction (IPHJ) structure and incorporating an additional liquid crystal film, a CPL detector with an outstanding g-factor of 1.62 is developed. Unfavorable charge injection is effectively suppressed by the IPHJ structure, which reduces the dark current of the organic photodetector. Consequently, a left CPL detectivity of 6.16 × 1014 Jones at 640 nm is realized, surpassing all of the latest photodiode-type CPL detectors. Adopting a liquid crystal film with adjustable wavelengths of selectively reflected light, the hybrid device achieves narrow dual-band CPL detection, varying from 530 to 640 nm, with a half-maximum full width below 90 nm. Notably, the device achieves excellent stability of 260 000 on/off cycles without attenuation. To the best of the authors' knowledge, all these features have rarely been reported in previous work. The CPL detector arrays are also demonstrated for encrypted communications and color imaging.

High Mobility Emissive Excimer Organic Semiconductor Towards Color-Tunable Light-Emitting Transistors.

Organic light-emitting transistors (OLETs) are highly integrated and minimized optoelectronic devices with significant potential superiority in smart displays and optical communications. To realize these various applications, it is urgently needed for color-tunable emission in OLETs, but remains a great challenge as a result of the difficulty for designing organic semiconductors simultaneously integrating high carrier mobility, strong solid-state emission, and the ability for potential tunable colors. Herein, a high mobility emissive excimer organic semiconductor, 2,7-di(2-anthryl)-9H-fluorene (2,7-DAF) was reasonably designed by introducing a rotatable carbon-carbon single bond connecting two anthracene groups at the 2,7-sites of fluorene, and the small torsion angles simultaneously guarantee effective conjugation and suppress fluorescence quenching. Indeed, the unique stable dimer arrangement and herringbone packing mode of 2,7-DAF single crystal enables its superior integrated optoelectronic properties with high carrier mobility of 2.16 cm2 ⋅ V-1 ⋅ s-1 , and strong excimer emission with absolute photoluminescence quantum yield (PLQY) of 47.4 %. Furthermore, the voltage-dependent electrically induced color-tunable emission from orange to blue was also demonstrated for an individual 2,7-DAF single crystal based OLETs for the first time. This work opens the door for a new class of high mobility emissive excimer organic semiconductors, and provides a good platform for the study of color-tunable OLETs.

Unraveling the crucial role of trace oxygen in organic semiconductors.

Optoelectronic properties of semiconductors are significantly modified by impurities at trace level. Oxygen, a prevalent impurity in organic semiconductors (OSCs), has long been considered charge-carrier traps, leading to mobility degradation and stability problems. However, this understanding relies on the conventional deoxygenation methods, by which oxygen residues in OSCs are inevitable. It implies that the current understanding is questionable. Here, we develop a non-destructive deoxygenation method (i.e., de-doping) for OSCs by a soft plasma treatment, and thus reveal that trace oxygen significantly pre-empties the donor-like traps in OSCs, which is the origin of p-type characteristics exhibited by the majority of these materials. This insight is completely opposite to the previously reported carrier trapping and can clarify some previously unexplained organic electronics phenomena. Furthermore, the de-doping results in the disappearance of p-type behaviors and significant increase of n-type properties, while re-doping (under light irradiation in O2) can controllably reverse the process. Benefiting from this, the key electronic characteristics (e.g., polarity, conductivity, threshold voltage, and mobility) can be precisely modulated in a nondestructive way, expanding the explorable property space for all known OSC materials.