Xiaolan Qiao

Synthesis, structure, and opto-electronic properties of regioisomeric pyrene-thienoacenes.

Three regioisomeric sulfur-bridged pyrene-thienoacenes (PTAs) have been synthesized. The crystal structures and optoelectronic properties of these ring-fused PTAs and their ring-opened precursors have been fully investigated. Among these isomers, the [3,4]-extended compound (4-S-PTA) shows the most pronounced spectral red-shift and highest quantum yield as well as large transistor mobility.

Tunable Field‐Effect Mobility Utilizing Mixed Crystals of Organic Molecules

High-quality mixed crystals with mixing-ratio-dependent lattice parameters and electronic structure are obtained by co-deposition of two organic molecules. Using the mixed films as the inducing layer in weak epitaxy growth, the mobility of VOPc transistors is finely tuned. This is possible because of the cooperative effect between the tunable lattice parameters and electronic structure.

A solution-processable dicyano-substituted quinoidal oligothiophene for air-stable ambipolar organic field-effect transistors

A novel solution-processable dicyano-substituted quinoidal oligothiophene molecule CDT-2T(CN)4 was synthesized and characterized. CDT-2T(CN)4 displayed high thermal stability and broad thin film absorption in the near IR region. Electrochemical results showed that CDT-2T(CN)4 exhibited reversible oxidation and reduction peaks with the LUMO energy level at −4.2 eV and the HOMO energy level at −5.3 eV. The solution processed thin film transistors of CDT-2T(CN)4 displayed electron-dominant ambipolar transport behavior under ambient conditions. The optimal saturation hole and electron mobilities were 0.003 and 0.023 cm2 V−1 s−1, respectively, one of the highest values for solution processed quinoidal based ambipolar organic semiconductors with good ambient stability.

Nitrile-substituted thienyl and phenyl units as building blocks for high performance n-type polymer semiconductors

Two novel polymers PDPP3T-CN and PDPPTPT-CN containing nitrile-substituted thienyl and phenyl units were designed and synthesized. The influence of nitrile groups on the electronic properties and charge-carrier transport of the polymers was thoroughly investigated and highlighted by comparing with the corresponding non-nitrile substituted polymers. Experimental results showed that the introduction of nitrile groups lowered the HOMO and LUMO energy levels of polymers by about 0.3 eV and 0.2 eV, respectively. Thin film transistor characteristics displayed that both polymers exhibited electron-dominated ambipolar behavior under ambient conditions. The highest electron/hole mobilities were 0.18/0.0083 cm2 V−1 s−1 for PDPPTPT-CN and 0.09/0.0017 cm2 V−1 s−1 for PDPP3T-CN, one of the highest electron mobilities for DPP-based polymers measured under ambient conditions with bottom-gate/top-contact device configurations.

Efficient broad-spectrum parallel tandem organic solar cells based on the highly crystalline chloroaluminum phthalocyanine films as the planar layer

Efficient parallel tandem organic solar cells are demonstrated by using the highly crystalline chloroaluminum phthalocyanine (AlClPc) films as the planar layer. Their broad photoresponse from 400–900 nm is contributed to the strong near-infrared absorption of the AlClPc films and the good complementarity between AlClPc and zinc phthalocyanine. Importantly, the high external quantum efficiency is obtained in the entire response range with the peak value 65% due to the high carrier mobility of the AlClPc films, and correspondingly the high power conversion efficiency of 3.5% is attributed to the large short circuit current density of 12.15 mA/cm2.

High performance thin film transistors based on bi-thieno[3,4-c]pyrrole-4,6-dione-containing copolymers: tuning the face-on and edge-on packing orientations

Bi-thieno[3,4-c]pyrrole-4,6-dione (bi-TPD) and oligothiophene copolymer semiconductors P1–P4, with different alkyl side chain densities and orientations, were synthesized. Their physicochemical properties were systematically characterized. With trimethoxy(octadecyl)silane (OTMS) modified SiO2 as substrates, the as-spun thin films of P1, P3 and P4 adopted the face-on packing structure while the P2 films displayed the edge-on packing arrangement. The packing differences of P1–P4 were ascribed to their different alkyl chain densities and orientations. The higher alkyl chain density is favorable to the face-on packing structure. After thermal annealing, the packing orientation of P2 remained and the packing structures of P1, P3 and P4 changed. P1 and P4 based films exhibited the coexistence of the edge-on and face-on packing structures in which the edge-on structure was predominant, and P3 based thin films were converted to the edge-on packing arrangement. The relationship between the aggregation structures and charge carrier transport properties of these films was explored through thin film transistors. All devices exhibited p-channel behavior with a maximum mobility larger than 1.0 cm2 V−1 s−1. Interestingly, the P3 films with face-on packing structures displayed a high mobility up to 1.18 cm2 V−1 s−1 (average mobility of 1.02 cm2 V−1 s−1), very close to the edge-on packed films which showed a maximum mobility of 1.4 cm2 V−1 s−1 (average mobility of 1.16 cm2 V−1 s−1). These results demonstrated, similar to edge-on packing structures, the face-on packing arrangement with π–π interactions facilitated charge carrier transport.

High-performance n-channel field effect transistors based on solution-processed dicyanomethylene-substituted tetrathienoquinoid

A solution-processable tetrathienoquinoidal semiconductor CMHT was synthesized and characterized. Single crystal diffraction results showed that CMHT adopted slipped π–π stacking in the crystal structure. Multiple intermolecular interactions, such as S⋯N and S⋯C (where C is the carbon on the cyano group), existed among neighboring molecules, which formed a 2-dimensional charge transport network. Solution-processed thin film transistors of CMHT displayed a high electron mobility of up to 0.22 cm2 V−1 s−1 under ambient conditions, one of the highest electron mobilities for quinoidal semiconductors. The correlation between the molecular packing of the CMHT and transistor performance was studied by AFM and XRD.

Modulating Surface Morphology and Thin-Film Transistor Performance of Bi-thieno[3,4-c]pyrrole-4,6-dione-Based Polymer Semiconductor by Altering Preaggregation in Solution

Due to their strong intermolecular interactions, polymer semiconductors aggregate in solution even at elevated temperature. With the aim to study the effect of this kind preaggregation on the order of thin films and further transistor performance, bi-thieno[3,4-c]pyrrole-4,6-dione and fluorinated oligothiophene copolymerized polymer semiconductor P1, which shows strong temperature-dependent aggregation behavior in solution, is synthesized. Its films are deposited through a temperature-controlled dip-coating technique. X-ray diffraction and atomic force microscopy results reveal that the aggregation behavior of P1 in solution affects the microstructures and order of P1 films. The charge transport properties of P1 films are investigated with bottom-gate top-contacted thin-film transistors. The variation of device performance (from 0.014 to 1.03 cm2 V–1 s–1) demonstrates the importance of optimizing preaggregation degree. The correlation between preaggregation degree and transistor performance of P1 films is explored.