Photophore-Anchored Molecular Switch for High-Performance Nonvolatile Organic Memory Transistor.

Over the past decade, molecular-switch-embedded memory devices, particularly field-effect transistors (FETs), have gained significant interest. Molecular switches are integrated to regulate the resistance or current levels in FETs. Despite substantial efforts, realizing large memory window with a long retention time, a critical factor in memory device functionality, remains a challenge. This is due to the inability of an isomeric state of a molecular switch to serve as a stable deep trap state within the semiconductor layer. Herein, the study addresses this limitation by introducing chemical bonding between molecular switch and conjugated polymeric semiconductor, facilitating closed isomer of diarylethene (DAE) to operate as a morphologically stable deep trap state. Azide- and diazirine-anchored DAEs are synthesized, which form chemical bonds to the polymer through photocrosslinking, thereby implementing permanent and controllable trapping states nearby conjugated backbone of polymer semiconductor. Consequently, when diazirine-anchored DAE is blended with F8T2 and subjected to photocrosslinking, the resulting organic FETs exhibit remarkable memory performance, including a memory window of 22 V with a retention time over 106 s, a high photoprogrammable on/off ratio over 103, and a high operational stability over 100 photocycles. Further, photophore-anchored DAEs can achieve precise patterning, which enables meticulous control over the semiconductor layer structure.

Visible-Light Communication with Lighting: RGB Wavelength Division Multiplexing OLEDs/OPDs Platform.

A multichannel/multicolor visible light communication (VLC) system using entirely organic components, including organic light emitting diodes (OLEDs) and organic photodiodes (OPDs), is developed to demonstrate indoor lighting applications where the integration of OLEDs and OPDs has significant potential. To achieve this, tricolor (Red/Green/Blue(R/G/B))-selective OPD arrays for the receiver and tricolor OLED arrays for the emitter are developed. For (R/G/B)-selective OPDs, a Fabry-Pérot electrode to enhance color selectivity and a thick junction structure to effectively accommodate a wide range of driving voltages are introduced. For tricolor OLEDs, fluorescent-emitting materials are used to enhance the operating frequency in addition to introducing a cavity structure to achieve narrow emission. Utilizing these spectrally refined tricolor OPDs/OLEDs, a VLC system is designed for indoor lighting applications, and a systematic analysis of their signal-to-interference ratio dependence on the distance or angle between the transmitter and receiver is performed. The study's findings indicate the importance of emission angle-dependent wavelength shift of the OLED and the luminosity function, which varies with wavelength, in the R/G/B mixed-white-light-based VLC systems. Finally, the feasibility of VLC using tricolor OPDs/OLEDs in the real-life context of indoor white-color lighting is demonstrated, showing that the transmitted data patterns well-matched the received data patterns.

Shortwave Infrared Organic Photodiodes Realized by Polaron Engineering.

A novel approach for developing shortwave IR (SWIR) organic photodiodes (OPDs) using doped polymers is presented. SWIR OPDs are challenging to produce because of the limitations in extending the absorption of conjugated molecules and the high dark currents of SWIR-absorbing materials. Herein, it is shown that the conversion of bound polarons to free polarons by light energy can be utilized as an SWIR photodetection mechanism. To maximize the bound-polaron density and bound-to-free polaron ratio of the doped polymer film, the doping process is engineered and dopant molecules are diffused into the crystalline domain of the polymer matrix and a direct correlation between the bound-to-free polaron ratio and device performance is confirmed. The optimized double-doped SWIR OPD exhibits a high external quantum efficiency of 77 100% and specific detectivity of 1.11 × 1011 Jones against SWIR. These findings demonstrate the application potential of polarons as alternatives for Frenkel excitons in SWIR OPDs.

Liquid-Film Rupture for Web-like Ag Nanowires toward High-Performance Organic Schottky Barrier Transistors.

Organic vertical transistors are promising device with benefits such as high operation speed, high saturation current density, and low-voltage operation owing to their short channel length. However, a short channel length leads to a high off-current, which is undesirable because it affects the on-off ratio and power consumption. This study presents a breakthrough in the development of high-performance organic Schottky barrier transistors (OSBTs) with a low off-current by utilizing a near-ideal source electrode with a web-like Ag nanowire (AgNW) morphology. This is achieved by employing a humidity- and surface-tension-mediated liquid-film rupture technique, which facilitates the formation of well-connected AgNW networks with large pores between them. Therefore, the gate electric field is effectively transmitted to the semiconductor layer. Also, the minimized surface area of the AgNWs causes complete suppression of the off-current and induces ideal saturation of the OSBT output characteristics. p- and n-type OSBTs exhibit off-currents in the picoampere range with on/off ratios exceeding 106 and 105, respectively. Furthermore, complementary inverters are prepared using an aryl azide cross-linker for patterning, with a gain of >16. This study represents a significant milestone in the development of high-performance organic vertical transistors and verifies their applicability in organic electronic circuitry.

Azide-functionalized ligand enabling organic-inorganic hybrid dielectric for high-performance solution-processed oxide transistors.

We propose a highly efficient crosslinking strategy for organic-inorganic hybrid dielectric layers using azide-functionalized acetylacetonate, which covalently connect inorganic particles to polymers, enabling highly efficient inter- and intra-crosslinking of organic and inorganic inclusions, resulting in a dense and defect-free thin-film morphology. From the optimized processing conditions, we obtained an excellent dielectric strength of over 4.0 MV cm-1, a high dielectric constant of ~14, and a low surface energy of 38 mN m-1. We demonstrated the fabrication of exceptionally high-performance, hysteresis-free n-type solution-processed oxide transistors comprising an In2O3/ZnO double layer as an active channel with an electron mobility of over 50 cm2 V-1 s-1, on/off ratio of ~107, subthreshold swing of 108 mV dec-1, and high bias-stress stability. From temperature-dependent I-V analyses combined with charge transport mechanism analyses, we demonstrated that the proposed hybrid dielectric layer provides percolation-limited charge transport for the In2O3/ZnO double layer under field-effect conditions.