Yu-Tai Tao

Films of the discotic liquid crystalline hexabenzocoronene (HBC) derivative, HBC-1,3,5-Ph-C₁₂, were prepared on the quartz substrate by the bar-coating method. Depending on the coating speed, regularly spaced stripes or continuous films were observed. In the former case, columns of the HBC derivatives align more along the stripes, which are perpendicular to the coating direction, whereas in the latter case, columns of the HBC derivatives in the film align more along the coating direction. These distinctive structures are confirmed via polarized optical microscopy (POM), polarized UV-vis spectroscopy, and grazing incidence small-angle X-ray scattering measurements.

A new class of fluorinated cyclopenta[2,1-b:3,4-b′]dithiophene (CPDT)-based small molecules, namely YC-oF, YC-mF, and YC-H, are demonstrated as hole-transporting materials (HTMs) for high-performance perovskite solar cells (PSCs).

Two organogelators, CO‐01 and CO‐03, featuring benzimidazole and long‐chain pyridine carboxyamide groups were prepared and their physical properties were fully explored. CO‐01 and CO‐03 are capable of transforming various organic solvents to organogels. The morphologic investigations of these organogels have shown that the supramolecular assemblies, in the forms of fibers and spheres, are readily generated from the aggregates of CO‐01 and CO‐03. The sol–gel interconversion can be readily achieved by tuning the gelator concentration and temperature. By manipulating the redox state of anthraquinone group in CO‐03, the gel–sol transition for the organogels of CO‐03 can be reversibly tuned by either chemical or electrochemical oxidation/reduction reactions. The presence of polarized imidazole and amide N–H groups allows anion‐induced gel collapse. The accompanying colorimetric and ratiometric fluorescent responses of gels CO‐01 and CO‐03 to F⁻ and CN⁻ render these organogelators being sensitive and selective anion probes.

Nonvolatile memory (NVM) devices were fabricated by implanting a self-assembled monolayer (SAM) of functional dithienylethene (DTE) derivative on the gold nanoparticle (Au-NP) surface in a pentacene-based organic transistor. The Au-NPs and DTE served as a charge-trapping medium and tunneling barrier layer, respectively. The transfer characteristic of the NVM device showed a narrow hysteresis window and wide memory window, indicating that the DTE-SAM served as a variable barrier layer to regulate the trapping and detrapping of external free charges at the Au-NPs. The energy gap introduced by the DTE-SAM is modulated through photoisomerization between a ring-open form and a ring-closed form by absorbing UV or visible light. For a memory device, the ring-closed DTE allows more free charge injection into the trapping sites, and the ring-open one better retains the trapped charges. A longer anchoring alkanethiol chain at the DTE moiety can further extend the device’s retention time. For the NVM operation, programming with the ring-closed DTE and then switching the DTE structure to the ring-open form for erasing can facilitate the charge trapping and charge retention with the same molecule compared to operating all in the ring-open form or all in the ring-closed form of DTE. The structural characterization and electronic characteristics of these devices are discussed in detail.

The self‐assembly behaviors, crystal morphologies, and charge transporting properties of π–conjugated framework can be strongly affected by the functional group/substituent it carries, as well as the way the film is prepared. In this work, thin films of mono‐ and di‐alkylated [1]benzothieno[3,2‐b][1]‐benzothiophene (BTBT) derivatives were prepared on a silicon substrate by solution‐shearing method. Their film morphologies and crystal packing details were examined using polarized optical microscope, grazing incident wide‐angle X‐ray scattering, and atomic force microscope. With 2‐tridecyl[1]benzothieno[3,2‐b][1]‐benzothiophene (C13‐BTBT), a film with well‐aligned molecules packed in face‐to‐face π‐stacking arrangement was obtained, rendering a 1D‐like charge conduction channel. For 2,7‐bis‐tridecyl[1]benzothieno[3,2‐b][1]‐benzothiophene (C13‐BTBT‐C13), well‐aligned molecules packed in a layered‐herringbone arrangement were obtained. With these films as a conducting channel in transistor fabrication, high‐field‐effect mobility was realized for C13‐BTBT‐C13, with a maximum mobility (μ_h) of 0.645 cm² /Vs and low anisotropic effect, presumably owing to the 2D growth of the π–conjugated skeleton in LHB packing. This study demonstrated the advantage of 2D semiconducting channels formed from C13‐BTBT‐C13 by low‐cost and scalable solution‐shearing processes, necessary for practical use in industry‐level and future flexible electronics.