Browsing by Author "He, Zhengran"

Now showing 1 - 6 of 6
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    Conjugated Polymer Controlled Morphology and Charge Transport of Small-Molecule Organic Semiconductors
    (Nature Portfolio, 2020) He, Zhengran; Zhang, Ziyang; Bi, Sheng; Chen, Jihua; Li, Dawen; University of Alabama Tuscaloosa; Columbia University; Dalian University of Technology; United States Department of Energy (DOE); Oak Ridge National Laboratory; Center for Nanophase Materials Sciences
    In this study, we report an effective approach to tune the crystallization, microstructure and charge transport of solution-processed organic semiconductors by blending with a conjugated polymer additive poly(3-hexylthiophene) (P3HT). When 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) was used as a model semiconductor material to mix with different amount of P3HT, their intermolecular interactions led to distinctive TIPS pentacene film morphologies, including randomly-oriented crystal ribbons, elongated needles with enhanced long-range order, and grasslike curved microwires with interlinkages. Each type of morphology was found to further correlate to considerably different charge transport and device performance. As compared to pristine TIPS pentacene devices, bottom-gate, top-contact OTFTs with 2% in weight P3HT additive showed a 2-fold and 5-fold improvement of average field-effect mobility and performance consistency (defined as the ratio of average mobility to the standard deviation), respectively. The improvement in transistor electrical performance can be attributed to the combined effect of enhanced crystal orientation and uniformity, as well as increased areal coverage. This work can be applied beyond the particular example demonstrated in this study and to tune the charge transport of other small-molecule organic semiconductors in general.
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    Dynamic photonic perovskite light-emitting diodes with post-treatment-enhanced crystallization as writable and wipeable inscribers
    (Royal Society of Chemistry, 2021) Bi, Sheng; Zhao, Wei; Sun, Yeqing; Jiang, Chengming; Liu, Yun; He, Zhengran; Li, Qikun; Song, Jinhui; Dalian University of Technology; University of Maryland College Park; University of Alabama Tuscaloosa
    Controllable photonic patterns have attracted great attention for various applications in displays, smart sensors, and communications. Conventional patterned light-emitting-diode (LED) systems require complicated design, complex procedure, and advanced equipment. Moreover, permanent properties of the fabricated patterns on LED restrict it from various important applications. Herein, we present an innovative writable and wipeable perovskite light-emitting-diode (WWPeLED) device, which tactfully utilizes the large variation of turn-on voltage originating from the external quantum efficiency (EQE) difference under controllable thermal treatment. The turn-on voltages with/without thermal-treatment devices exhibit a large gap of over 5 V, and the thermal-treatment electroluminescence intensity is more than 10 times higher than that of non-thermal-treatment devices. The new phenomena open up an effective way of controlling illumination with desired pattern designs. Additionally, the distinct handwriting fonts and habits as well as printing patterns with illumination WWPeLED are also realized. Furthermore, these written and printed features can be totally wiped out with an 11 V cleaning voltage, turning the devices as a regular fully bright PeLED. The stability and repeatability tests prove the robustness of WWPeLED in both mechanical and electroluminescence performance after a long period of operations. The innovative WWPeLED devices may find prospective applications in various optoelectronic devices and flexible integrated systems.
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    Polyferrocenylsilane Semicrystalline Polymer Additive for Solution-Processed p-Channel Organic Thin Film Transistors
    (MDPI, 2021) He, Zhengran; Zhang, Ziyang; Asare-Yeboah, Kyeiwaa; Bi, Sheng; Chen, Jihua; Li, Dawen; University of Alabama Tuscaloosa; Columbia University; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Dalian University of Technology; United States Department of Energy (DOE); Oak Ridge National Laboratory; Center for Nanophase Materials Sciences
    In this study, we demonstrated for the first time that a metal-containing semicrystalline polymer was used as an additive to mediate the thin film morphology of solution-grown, small-molecule organic semiconductors. By mixing polyferrocenylsilane (PFS) with an extensively-studied organic semiconductor 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene), PFS as a semicrystalline polymer independently forms nucleation and crystallization while simultaneously ameliorating diffusivity of the blend system and tuning the surface energies as a result of its partially amorphous property. We discovered that the resultant blend film exhibited a 6-fold reduction in crystal misorientation angle and a 3-fold enlargement in average grain width. Enhanced crystal orientation considerably reduces mobility variation, while minimized defects and trap centers located at grain boundaries lessen the adverse impact on the charge transport. Consequently, bottom-gate, top-contact organic thin film transistors (OTFTs) based on the TIPS pentacene/PFS mixture yielded a 40% increase in performance consistency (represented by the ratio of average mobility to the standard deviation of mobility). The PFS semicrystalline polymer-controlled crystallization can be used to regulate the thin film morphology of other high-performance organic semiconductors and shed light on applications in organic electronic devices.
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    RETRACTED: Wavelength modulation of ZnO nanowire based organic light-emitting diodes with ultraviolet electroluminescence (Retracted article. See vol. 11, pg. 893, 2021)
    (Royal Society of Chemistry, 2020) Chen, Runze; Liu, Chuan; Asare-Yeboah, Kyeiwaa; Zhang, Ziyang; He, Zhengran; Liu, Yun; Dalian University of Technology; Pennsylvania State University; Columbia University; University of Alabama Tuscaloosa
    Although organic light emitting diodes (OLEDs) can find important applications in display-related fields, it still remains a challenge to fabricate high-efficiency ultraviolet (UV) OLEDs with tunable wavelength. In this work, we demonstrate a facile method to adjust the electroluminescence (EL) peak from an inverted UV-OLED device that has zinc oxide nanowires (ZnO NWs) as an electron injection layer. The organic-inorganic interface between ZnO NWs and the 3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole (TAZ) emission layer employed in this work allows a reduction of the diffusion length of excitons, which further results in a hampered relaxation process of higher energy states as well as a blue shift of the EL spectrum. As a result, the emission peaks of the UV-OLED can be easily adjusted from 383 nm to 374 nm by tuning both the length of the ZnO NWs and the thickness of the TAZ emission layer. Our work reveals an important correlation between emission peaks and exciton diffusion, and presents a novel approach to fabricate high-performance UV-OLEDs with the capability of facilely modifying the emission wavelength.
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    RETRACTION: Wavelength modulation of ZnO nanowire based organic light-emitting diodes with ultraviolet electroluminescence (Retraction of Vol 10, Pg 23775, 2020)
    (Royal Society of Chemistry, 2021) Chen, Runze; Liu, Chuan; Asare-Yeboah, Kyeiwaa; Zhang, Ziyang; He, Zhengran; Liu, Yun; Dalian University of Technology; Pennsylvania State University; Columbia University; University of Alabama Tuscaloosa
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    Tips pentacene crystal alignment for improving performance of solution processed organic thin film transistors
    (University of Alabama Libraries, 2014) He, Zhengran; Li, Dawen; University of Alabama Tuscaloosa
    A newly-developed p-type organic semiconductor 6,13-bis (triisopropylsilylethynyl) pentacene (TIPS pentacene) demonstrates various advantages such as high mobility, air stability and solution processibility, but at the same time its application is restricted by major issues, such as crystal misorientation and performance variation of organic thin-film transistors (OTFTs). This dissertation demonstrates several different approaches to address these issues. As a result, both crystal orientation and areal coverage can be effectively improved, leading to an enhancement of average mobility and performance consistency of OTFTs. Chapter 1 presents an introduction and background of this dissertation. Chapter 2 explores the usage of inorganic silica nanoparticles to manipulate the morphology of TIPS pentacene thin films and the performance of solution-processed organic OTFTs. The resultant drop-cast films yield improved morphological uniformity at ~10% SiO2 loading, which also leads to a 3-fold increase in average mobility and nearly 4-times reduction in the ratio of standard deviation of mobility (μStdev) to average mobility (μAvg). The experimental results suggest that the SiO2 nanoparticles mostly aggregate at TIPS pentacene grain boundaries, and that 10% nanoparticle concentration effectively reduces the undesirable crystal misorientation without considerably compromising TIPS pentacene crystallinity. Chapter 3 discusses the utilization of air flow to effectively reduce the TIPS pentacene crystal anisotropy and enhance performance consistency in OTFTs. Under air-flow navigation (AFN), TIPS pentacene forms thin films with improved crystal orientation and increased areal coverage, which subsequently lead to a four-fold increase of average hole mobility and one order of magnitude enhancement in performance consistency. Chapter 4 investigates the critical roles of lateral and vertical phase separation in the performance of the next-generation organic and hybrid electronic devices. A novel method is demonstrated here to switch between lateral and vertical phase separation in semiconducting TIPS pentacene/ polymer blend films by simply varying the alkyl length of the polyacrylate polymer component. The phase separation modes depend on intermolecular interactions between small molecule TIPS pentacene and polymer additives. The blend film with a dominant vertical phase separation exhibits a significant enhancement in average mobility and performance consistency of organic OTFTs. Chapter 5 demonstrates an effective approach to improve both charge transport and performance consistency in solution-processed OTFTs by blending TIPS pentacene with a series of small-molecule additives: 4-butylbenzoic acid (BBA), 4-hexylbenzoic acid (HBA), and 4-octylbenzoic acid (OBA). These three small molecules share a benzoic acid moiety, but have different length of hydrophobic tails. The self-assembled interfacial layer of small molecules on the gate oxide surface leads to uniform deposition of TIPS pentacene crystal seeds and facilitates TIPS pentacene to grow along the tilted orientation of substrate, which results in a film of enhanced crystal orientation and areal coverage. OTFTs based on TIPS pentacene/small molecule blends demonstrate greatly improved average hole mobility and performance consistency, which correlates with the length of hydrophobic tail of the small-molecule additives. Chapter 6 summarizes the conclusions of this dissertation and the related future work.